For those trying to run boost through their MY2000-2001 and and can't get the car above 2psi, there is a REALLY cheap way to fix this. The MAP sensor sends a voltage to the ECU ranging from .4 to 4.8V depending on the pressure. If the sensor sees more pressure than it was designed to handle (aka boost), it tries to send the ECU a signal that is out of range, thus causing the car to buck and hesitate. By installing a $ .10 zener diode to the ECU, you can now limit the maximum signal the ECU will see.

We used a 4.7 volt 1 watt axial lead diode # 1N4732 and soldered it into the ECU. Under 4.7 Volts, the diode does nothing to the MAP signal, allowing the car to run totally normal off of boost. The moment the MAP sends more the 4.7 V, the diode bleeds it off thru its ground and limits the signal at 4.7 V. Ideally, a 4.8V diode would be best as it would allow for a little more injector duty cycle, but we haven't found any yet. Maybe a S-afc could allow us to get that last .1 V before the ECU goes nuts.

Everything is done inside the ECU. Solder the Cathode end (with the stripe) to Pin #5 on ECU plug B136 ( it goes to a Pink with blue wire on the harness). Fortunately, the pin that needs to be soldered to is on top.
On the other end of the diode, solder a small piece of fine gauge wire with a small ring terminal on the other end. Ground the ring terminal under one of the ECU case mount screws. You should cover any exposed leads with some insulation. Be careful when working on your ECU and do so at your own risk( disclaimer).

Don't forget that your ECU has no idea that there is any boost, so all enrichment needs to be done by other meathods like a fuel pressure riser, etc. With only a 80 psi pump and a FPR, this diode setup seems to work up to 6 psi boost. Be careful when boosting your car and do so at your own risk (disclaimer).

You can find these zener diodes at good electronics stores. Try Newark Electronics at www.newark.com. (http://www.newark.com.) They have a Motorola 4.7 V diode that is 500mW, part # 1N4688. I am guessing that that should be OK. We have the 1W units in stock though.

Free info for happy boosting!
Andy at RalliSpec

Nice!

Sure beats buying a whole reprog ecu and turbo map sensor!

The diode trick is an old trick... and is a crude boost cut defender...

It acts as a voltage clamp...simple.. http://www.i-club.com/ubb-files/smile.gif

I am sure something liek the adjustable HKS fuel cut defender will do the same trick..maybe better ?

I'm suprised Rallispec (as a reputable tuner) are promoting this ? (No offence guys)

J.

Before I went Tech II, I used my AFC to enrich as far as I could. If I went to far with it, like +28% or something, the car would buck wildly. Not saying this is at all the case, just some food for thought http://www.i-club.com/ubb-files/smile.gif


MattC

Andy did this to my car just the other week. It works great and im running 6psi with only a fpr and fuel pump. No pinging. Thanks Rallispec!!
PS: I think Rallispec is telling us this so we dont spend $200 for some black box that does the same thing.

[This message has been edited by nathan power (edited January 20, 2001).]

That's weird though, cause my Hyper R is set to +30% at the higher rpms, yet it still runs lean.

Definitely have to look into a fpr.

Good work, Andy. This sounds like an easy mod. However, I'm not entirely comfortable with installing a zener diode directly to the MAP sensor output. You may be drawing large currents when the zener is doing its clamping function.

I'd recommend adding a small series resistor to limit the current that the zener diode is shunting to ground. Something like this:

MAP Sensor ECU Map
Out Resistor In
O----o---\/\/\/---o--------O
|
|
|---|
Zener / \
Diode ---
|
|
-----
GND ---
-

A 10 ohm resistor should be sufficient.

A preferred method would be to use a clamping circuit that uses an op-amp in combination with the above circuit to obtain a sharper clamping characteristic. Or better yet, design one with an adjustable clamping voltage as well.

-WaC
Wayne

Edit: spelling.

[This message has been edited by wac (edited January 20, 2001).]

There’s away to determine if that resistor is really needed.

If the MAP’s output impedance is anywhere near that of the MAF (over 20k), the resistor is not needed - the MAP’s output can be inadvertently shorted to ground indefinitely without damaging the sensor. The current would only be in the order of microamps.

One can determine the MAP’s output impedance using a crude but effective technique. You’ll need a multimeter (preferably a DMM) and a 100k potentiometer (a trimmer pot is fine enough).

The trick is to get the MAP’s output stable during the measurement. In other words the manifold vacuum should be kept constant. You can try this on idle but the output would be too low to make a meaningful measurement (since the manifold vacuum would be so high). I suggest performing this test with the ignition on, but the motor not running. The MAP will output a signal reflecting 1 atmosphere above vacuum. Its output voltage will not be near as high as 5V but that doesn’t matter as long as it’s steady.

1) Before connecting the pot to the MAP, measure and note the MAP’s output voltage.
2) Connect the pot between the MAP’s output and ground (i.e. the pot’s wiper contact and one end contact).
3) While the multimeter is connected to the MAP output, adjust the pot until you obtain an output reading roughly 1/2 the previously noted voltage.
4) Remove the pot and measure (record) its value with the multimeter.

That recorded value can be read (interpreted) as the approximate MAP output impedance.

Regards,
Ed.

[This message has been edited by edekker (edited January 20, 2001).]

Well, whatever the case is, it sure beats JC Sports' expensive magical black box which they can't/won't tell us how it works.

Hmm..I thought everyone already knew that JC's "magic black box" is pretty much the J&S fuel controller (which in essense is a voltage clamp).

On another note, my car (auto) in the first 2 gears run great (rich), but it runs lean in the 3rd and 4th gears. This was proven on the dyno at Technik. Now my question is, yesterday driving on the highway at about 130-140km, I experienced a slight "bucking" so I immediately backed off. Now mind you I KNOW of the lean run condition up top and I was listening for pinging, which thankfully I didn't hear. What I'm wondering is what that "bucking" was? It feels like the same bucking I got before I got the MAP fix, so why would that same problem be back again? Anyone?

BUMP! I didn't see this, so I am sure there are others that haven't seen it as well.

thanks rallispec!

Yah, Rallispec kicks A$$.

Thanks for sharing. This helps alot of us out.

Quick question, maybe it's silly but...
would going the TEC-II route totally bypass this problem? Also, does this "boost issue" happen on all MY00-MY01 cars?
~Frank

Tec-ii completely bypasses this problem (and almost any other boost problem too!) Only MAP based cars need to worry about this (my 00 and 01) MAF based cars have their own set of problems.

Yeah Jay,

I was shocked when one of my friends took apart the HKS fuel cut defencer. He was told by several people that he just paid $200+ for some resistors and a couple other basic parts. Sure enough, that's what he found when he took it apart.

Keiho - My car would do the same, at 5 psi it would run fine in 1st - 3rd (manual) and lean in 4th and 5th and buck in top gears WOT - I turned up fuel pressure and the problem went away (unless I turn up the boost and go lean again).

If I set the fuel pressure higher to prevent this "lean bucking" at 7-8 psi in 4th and 5th, then when I drop to 5 psi the car runs too rich in all 5 gears... That is why I am ditching the RRFPR for the SD controller and extra injectors.

I got a CE light with it once when it was bucking, and it was misfires in cylinder #3 and #4 with no audible pinging. My Denso iridium spark plugs looked great when we pulled them, with no signs of detonation and good color.

Don't you have a MY00/01 turbo kit, and if so, why are you still using a Hyper-R? Especially since the voltage clamp limits it's usefullness for top end. When I had the S-AFC I could make the car sputter if I turned up enrichment too high above 5,000 rpm under boost (but was fine without boost). If you installed the Hyper-R after the voltage clamp, then you know why it bucks like it used to - you are sending too much MAP voltage to the ECU. Again, I recommend the JCS torque chip II like I got, and using a RRFPR or extra injectors for top end tuning, if you cannot afford a TECII kit from vishnu yet.

Larry www.ImprezaRS.com (http://www.ImprezaRS.com)

Well the Hyper R was taking care of the lower end, had I KEPT my turbo (I sold it and am now back into the NA camp! http://www.i-club.com/ubb-files/smilies/biggrin.gif ) I would've got a RRFPR and that would've taken care of probably everything as you've already documented quite nicely. http://www.i-club.com/ubb-files/smilies/smile.gif

Sigh...I kinda miss the quietness of the turbo...up until I let her rip and the wastegate just roars and scares the heck out of people!! http://www.i-club.com/ubb-files/smilies/biggrin.gif http://www.i-club.com/ubb-files/smilies/biggrin.gif http://www.i-club.com/ubb-files/smilies/biggrin.gif

I'm going turbo with a JC kit (with a T28 ball bearing!)from a friend of mine and was wondering who has installed an HKS or J&S fuel cut defencer?

I have a J&S from my Supra days and want to re-use it now.

Why buy a JC chip when I have this? I also got in yhr kit a ITC and a S-AFC !

Help Guys!

Oh, the turbo kit was mounted on a 99 and is going in mu 00 sedan.

Thanks in advance!
Leo

Leo-
To boost your my00 you will need a voltage clamp or check valve (which you have) and a RRFPR (which you dont) in addition to this you might want a split second TC-1 (timing via boost *and* rpm), a SAFC, and a knock senor. all depending on how high of boost you want. Basically with the stuff you have, add a rrfpr and you're good to 7psi. You'll need a fuel pump before you try for higher. (you may want a fuel pump at 7psi anyways.)

Hi!

The kit has a RRFPR, S-AFC, Fuel pump, and ITC.

I have the J&S FCD, HKS EVC EZ, HKS Twin Poewr, and HKS Turbo Timer.

My friend is running 10-12 psi but I'm happy with 5-7 psi. I don't want to blow tranies like him (4 at this time) If anything with the EVC, I can take it up for limited periods for some races that merit it but otherwise, I'm staying low boost.

What I need is the way to wire in the J&S, and to put it before or after the AFC.

Thanks in advance!
Leo

lagging.com had the SAFC diagram. The clamp goes on your map voltage line on the ECU side of the line from the safc. (that way you cant over enrich and cause fuel cut)

I pm rallispec, I may be able to hook them up with the 4.8v diodes, my mother works for a rather large electronics company that sells all that kind of stuff, No promises, but if there is one place that can get them its where she works. Ill keep you all posted, if your interested....

Jay McDade
Auto Tech--Lincoln/Mercury/Jaguar

Jay, please do so and thanks!

Mid, so, when the line goes into the ECU I cut, splice in the clamp and right after I put the AFC?

I'll be doing this hopefully by the end of the month, so I might send the up and down pipes to JetHot or might wrap them with termotec(sp?)

Leo

www.radioshack.com (http://www.radioshack.com) is a good source for the diodes.
I just ordered 10 of them so I will have some extras. These are the 1w variety too. I can mail a couple out if people would like.

I have a question about the need to limit the voltage from the MAP. Would it be better to scale it down, so that the output voltage is still proportional to the pressure (so instead of 4.8V=3psi, now 4.8V=10psi...these r phoney #'s, just to illustrate the point)?

I assume that the voltage is used to calculate the injector duty cycle. If that's the case, then you'd have a maximum duty cycle for any pressure larger than the maximum allowed by the ECU when you use the clamp.

I'm an EE and I'd be happy to design something (cheap) for you if you think that there is a better way...i just have limited turbo knowledge, so you'd have to tell me exactly what you'd want it to do.

Scaling wont work as there is only a 1 bar MAP. Ie once you hit max signal, you hit max signal. For scaling to work right, you'd need the MAP to produce more than 5V and I dont think it'll do that. However a 2 bar map, scaling the voltage and a standard FPR might be able to regulate it... probably more trouble than its worth though.

If the max output of the MAP is only 5V, then you're right, scaling won't work. I was assuming it would go much higher than that (12V).

Hey it's pretty cool to see this helping other people.

My friends and I are in the prosses of switching over to subie from your FWD turbo Mopar's from the late 80's (cause Mopar perf. dropped the goodies for our cars http://www.i-club.com/ubb-files/smilies/frown.gif) and our Mopar perf. computers that run at 14.0-14.5 psi will cut at 15psi. this is because of the same thing as what your all talking about. (coinsidently our comp. cuts at 4.8v also witch the MAP puts out at 15psi) we used this exact fix when running over 14psi (and some of us do!!! http://www.i-club.com/ubb-files/smilies/biggrin.gifhttp://www.i-club.com/ubb-files/smilies/biggrin.gifhttp://www.i-club.com/ubb-files/smilies/biggrin.gifhttp://www.i-club.com/ubb-files/smilies/biggrin.gif) one of the things you have to worry about (after the fuel of corse!) is ign. timeing. timeing is retarded as boost is increased (helps avoid the bad bang!), but when the diode tells the comp. that your holding at 14.5psi it stops retarding the timeing even though the fun pump is still on its way to 19psi!! to be safe we set our ign. timeing at the stock 12deg. instead of the 14-16deg. we used with 14psi as our max boost. for us the extra fuel was simple cause the 14psi comp. was a drop in cause the stock fues sys was good up to 15psi. for mor fun than that we through in a set of M.P. +20% injecters, a beter fuel pump that came from "another car" (don't say VW) one of us got ahold of a used adj. FPR that was made for a Buick GN and it was the same fit as our fixed FPR and was able to tune the beast for beter fuel mileage.

I think the 4.7v is the max allowable value to be read from the sensor. Anything higher, and the ECU goes into fuel cut. In theory, everything will function normally until 3psi and then the zener diode kicks in and tells the ECU that it is still running 3psi (though in reality, it is higher).

Hi y'all! Well, I've tried the MAP fix with the zener diode and it's not working properly.

This is what is happening when it is installed properly as per Rallispec instructions and common sense. (I don't think I could have messed this simple thing up. http://www.i-club.com/ubb-files/smilies/biggrin.gif)

As I accelerate in gear (3rd for the hell of it), the MAP output rises to roughly 3.4V and stays there from about 1/3 throttle to WOT. During that time, my car is happily bucking along the road, EGTs (2" from Cyl 3) are 1500+, A/F ratio is completely lean. Needless to say, I shutdown quickly. http://www.i-club.com/ubb-files/smilies/biggrin.gif

Soooo... I figured I'd change the 4.7V 1W zener diode for another identical one, but that didn't change anything. The MAP output gets stuck at ~3.4V and won't budge. Thus, the ECU probably isn't running the injectors at more than 1/2 duty cycle which explains the lean condition.

Why could this be happening? Heck, I thought a 4.7V zener would cut at 4.7V not at 3.4V. I double checked the part numbers on them and they're the correct ones.

Feeling kind of helpless tonight, I tried disconnecting the zener and went for a drive to make sure that the MAP sensor was actually working properly. And what a drive it was! WOAH, big-time power increase under 60% throttle and running rich! At 60% throttle to WOT I got about 5 volts and the bucking/lean condition returned which is no surprise.

Any ideas? I might go the check valve way, but man, I figured that the zener method is idiot proof. http://www.i-club.com/ubb-files/smilies/tongue.gif


ASR Stage 2 turbo kit @ 3 PSI http://www.i-club.com/ubb-files/smilies/biggrin.gif


(Moderators: how about moving this thread to the turbo forum?)



[This message has been edited by Rick Hunter (edited April 01, 2001).]

You know, I tried the diode thing too and I was getting the same results. Unfortunately, I don't have a way to monitor voltage but the symptoms that you are describing are exactly what's happening to me @3-5 lbs. I haven't tried removeing the diode yet though. Keep us posted as to what you are going to do to reslove the problem. I don't really wanna go out and drop $150 on one of those "magical boxes" (cause you know what's inside right....a diode that bleeds voltage http://www.i-club.com/ubb-files/smilies/smile.gif)

You could be using too big a diode (1 Watt). Try to find a smaller (lower power) 4.7V diode, preferably in a 200mW (500mW max) power rating.

Let me explain why…
Take a look at the diagram:

<IMG SRC="http://216.242.153.40/MembersList/UserPics/230/zener.jpg" border=0>

V[z] = the nominal zener voltage drop, when a test current I[ZT] is made through the diode.
V[R] = the nominal voltage drop (lower than V[z]), when a very small leakage current I[R] flows through it.

In specifying V[z], 1-Watt zener diodes are subjected to higher test currents, typically in the tens of milliamps (mA), compared to lower powered zener diodes. For example a 1-Watt zener diode, rated 4.7V@ I[ZT]=50mA, will clamp at 4.7V if the current flowing through it is equal to its rated I[ZT] of 50mA.

If the clamping current goes lower than I[ZT], then V[z] will go lower as well. V[z] will continue to go lower and even pass lower than the specified nominal value for V[R] as the clamp current is made lower than the specified leakage current I[R].

The problem is that the MAP output impedance is so high that, when the zener diode begins to clamp, the current flowing though it is in the hundreds of microamps – an amount considered akin to leakage current I[R] for big diodes.

I’m not saying this is the definite cause of your particular problem – it’s just an avenue to explore.

Ed.

Stimpy,

I have reread RalliSpec’s MAP fix description more carefully.
Not having a MY00 or MY01 RS to perform any testing myself, I can only comment, offer advice, or an opinion, but hopefully an informed one.

The device they use has the following specs:
1N4732
V[z]=4.7V@I[ZT]=53mA
V[R]=1V@I[R]=10uA
P[d]=1W
DO41 - Axial leaded, glass package

Firstly, make absolutely sure that the part is connected in the proper polarity, as RalliSpec pointed out:
The cathode (banded end) is connected to the MAP signal line; the anode is connected to ground (or MAP signal reference).

You should get the very same zener diode, bearing the same core (root) part number 1N4732 (1N4732A would be fine) – if only as a starting point from where a concerted decision can be made in regards what action one should take if the part fails to function as expected.

Be careful handling the diode. The package is made of delicate glass, which can easily crack if the leads are bent too sharply or with too much force.

An important point to remember is that the diode is not the be-all-to-end-all fix.
The zener diode is there only to prevent the ECU from entering into an undefined erratic behavioral mode. As RalliSpec pointed out, the fuelling requirements, at and above the point where the zener diode clamps the MAP output, still need to be dealt with as the tuner deems fit (i.e. RR-FPR, higher fuel pressure, supplementary fuel computers, etc).

A comment I would like to make is in regards to the choice RalliSpec made in the 1N4732.
While the zener diode obviously worked for them to a certain degree, they do not explicitly talk about the actual measured clamped voltage.

If the MAP sensor cannot output the necessary amount of current to satisfy I[ZT], it is quite possible that the clamped voltage had been a little lower than the specified nominal V[z] of 4.7V since the required I[ZT] of 53mA could not have been met. The lower current places the clamped voltage too tight around what’s called the ‘knee’ of the curve (somewhere between V[z] and V[R]).

That is not good because that area around the knee is not well defined. There will be poor part-to-part consistency since the clamped voltage V[z] had been expected to be 4.7V at a current much lower than the specified I[ZT] of 53mA. A particular zener diode may well work for one person; but for another person the zener diode, perhaps made and taken from a totally different batch, will not work so well.

IMHO, A smaller, lower-powered 200mW zener diode would offer a more dependable part-to-part consistency (repeatability) since its expected V[z] is specified at a much lower I[ZT].

Ed.

Ed, first of all.... THANK YOU!

You were absolutely right that a 1W Zener was too high. I bought and installed a 500mW 4.7V Zener and no more bucking or hestiation! http://www.i-club.com/ubb-files/smilies/biggrin.gif http://www.i-club.com/ubb-files/smilies/biggrin.gif http://www.i-club.com/ubb-files/smilies/biggrin.gif

I didn't have time to hook up a voltmeter to the MAP output tonight, but it sure seems to be clamping far above the 3.4V I got with the 1W 4.7V Zener. I'll hook up the voltmeter tomorrow and will let you know how it goes.

Thanks again!

Yeah, Tom from Ludespeed tried this and he got great results. Must have tried a lower power one right away. Good to hear that you've got your car running well again. http://www.i-club.com/ubb-files/smilies/smile.gif

Off to the turbo forum it is!

Could we take readings on how many mA the MAP sensor signal has and then size the zener diode appropriately? Go slightly larger than the max amperage for instance?

[EDIT] and why in the world is this working for Rallispec?

-Jon

[This message has been edited by stimpy (edited April 02, 2001).]

A slighty better solution can be obtained by using a series resistance.

mastervic27- Can you elaborate on this? or is it just something you heard?

edekker: Wow, thanks for the in depth reply.

Rick: where did you source the zener diode from?

I guess it looks like the general concensus is that the 1W version is too much and we must go down to a 500mW version. Or perhaps even slightly lower than that.

-Jon

[This message has been edited by stimpy (edited April 03, 2001).]

Important Zener Diode Update:

Turns out that the 4.7V 500mW Zener still leaked too much current. At WOT, it read 3.9V and caused a semi-lean condition that I initially miss interpreted as a bad RRFPR.

After trying a whole bunch of different Zeners, I happened to get lucky. This is the correct one: 5.1V 400mW - part number 1N751B. It reads 4.72V at WOT.

Now my A/F ratio reads mainly rich from 1000 rpm to redline in 2nd gear. It pulls smoothly without a hint of hesitation or bucking. Now all I have to do is get the high flow fuel pump and a better RRFPR to have some more fun. http://www.i-club.com/ubb-files/smilies/biggrin.gif

Ed, thanks again for pointing me in the right direction.

Stimpy: I searched a whole lot of local electronics shops here in Montreal and only one (Abra Electronics 514-731-0117) had the 5.1V 400mW 1N751B.

Glad to be of help, Rick.

Ed.

I am using a 1w 4.7v zener in a MY00. Works just fine, I have 5 lbs boost.

Blaster: That's quite some interesting news. Could you let us know how you're delivering more fuel? Via a high-flow pump and/or rrfpr? Different injectors?
Would it be possible to hook up a voltmeter to your map signal and post the results at WOT? I was limitted to roughly 3.4V with the 4.7V 1W 5% tolerance Zener.

It really would be interesting to see the results for other MY00-01 turbo projects.

ciao

Rick -

I am using a Walbro fuel pump and a Vortech 4:1 Fuel Management Unit (essentially a fixed rate FPR).

It is running reee-al rich right now because I don't have a full exhaust, but my boost gauge measures 5 lbs and fuel cutout doesn't happen til you hit the rev limiter.

It will probably be a while before I crack open my ECU again - have a few things to tidy up first (like that exhaust).

Skidplatez,

Just as Wac has mentioned on the first page, add a series resistance to limit the current. Refer to his drawing on the first page.

Just for referents, on my MY00 RS I'm running stock 34psi at idle and 42psi at WOT.

I figured I'd add something more to this discussion:

Part Vz @ Iz Datasheet Link
1N4688 4.7V@50uA http://www.onsemi.com/pub/Collateral/1N4678-D.PDF
1N750A 4.7V@20mA http://www.onsemi.com/pub/Collateral/1N746A-D.PDF
1N751A 5.1V@20mA http://www.onsemi.com/pub/Collateral/1N746A-D.PDF
1N5230 4.7V@20mA http://www.onsemi.com/pub/Collateral/1N5221B-D.PDF
1N5231 5.1V@20mA http://www.onsemi.com/pub/Collateral/1N5221B-D.PDF
1N4732 4.7V@53mA http://www.onsemi.com/pub/Collateral/1N4728A-D.PDF

I think using a 1N751 may be asking for trouble, especially if the MAP sensor is current-limited as Ed has suggested (I agree with his analysis). Ingo (Rick Hunter) has cheated a bit by going up to the next zener voltage, and I think he got lucky with his particular specimen of 1N751B (BTW, I could only find datasheets for the "A" model, so I presume the zener characteristics are similar). Some people may luck out with a 1N5231B as well, but I think it's a crapshoot.

The wattage rating of the diode does not necessarily relate to the zener current, although it's generally true. Wattage refers to how much heat the diode can dissipate. The zener voltage and zener current ratings determine where the knee of the curve occurs (see Ed's excellent description above). Adding a series resistor, as I suggested earlier, will not help if the MAP sensor is already output current-limited. I had suggested it in order to prevent sinking too much current from the MAP sensor, and it appears we don't have to worry about that in this case. Unless, of course, we're not current-limited, and we need add a series resistor to keep the reverse current to below 60 mA (see 1N4688 datasheet).

The ideal zener diode to use, then, is the 1N4688, with an extremely low 50 microamps of zener current at 4.7V. Unfortunately, you can't get it at Digi-Key, and less likely at Radio Shack. Arrow.com only sells it in 5000-piece tape-and-reel lots, at $0.057 each. (It's only $285 for a lifetime supply.) Perhaps someone can spend a little time tracking down a retail source?

-WaC
Wayne

Edit: typos

[This message has been edited by wac (edited April 09, 2001).]

Well, to throw some more craziness into the mix, I'm running the same setup as blaster (walbro, vortech 4:1) and I'm getting the bucking and hesitation at anything after 3psi of boost with the 1W 4.7V diode. It also threw a CE light.

But, there also might be something up with my fuel delivery. I'm getting under 25 lbs of fuel pressure at idle when i KNOW I should be getting more. And yes, I do have everything hooked up right http://www.i-club.com/ubb-files/smilies/smile.gif Anyone have any insight? Thanks.

~Off to try more diodes....

That is very odd. I just installed my walbro 255lph pump and at idle while stock, I received 38psi of fuel pressure, but now I am receiving 48psi fuel pressure.

I think something is amiss with your fuel delivery.

-Jon

48 huh? Hmm...I'll go back and double check the pump...

So the basic rule of thumb here is if we get a lower rated amperage, then it will come closer to hitting the peak 4.7v?

-Jon

Well, I took some time to track down a retail source for the 4.7V 50uA zenier and I think I found it at Newark Electronics (http://www.newark.com)

I typed in the zenier part # which was 1N4688 but came up with a 4.7V .25W zenier instead. I don't have my conversions down but I believe .25W=25uA. Am I correct or no? Would this diode work?

They sell them at a whopping $.09 each but there is a $5 surcharge for not purchasing up to $25 worth of merchandise. That and shipping and you're paying about ten bucks for a few 9 cent diodes. Is it worth it? Hmmmm..

I tried to check Newark's stock, but was greeted with the familiar poor site performance (I now remember why I only buy stuff from them via phone).

It seems that some manufacuteres do make 250mW versions, so I presume it's one of these that Newark is selling. However, even the 250mW version has the same zener voltage and current ratings as the 500mW version.

I have ordered 1N4688 samples, which I hope to get in about a week. PM or email me if you want to be a guinea pig to try one out (first 3 people only, please). There's a condition, of course: I would like to see some voltage readings using various diodes. Hopefully, these readings will provide clues as to the output impedance of the MAP sensor.

-WaC
Wayne

Hello,

Sent ya a PM http://www.i-club.com/ubb-files/smilies/smile.gif

Okay, so now I have driven the car more, and I have found a couple of circumstances where the 1w zener is not doing the job - in some low rpm (1800), light-mid throttle situations, I am getting a fuel cut at 3 lbs. Kinda weird, I would expect it only to happen at WOT, where voltage would likely be higher, but perhaps less current at lower throttle, and coming off the shoulder to a different region of the graph.

However, I can avoid this by staying on the throttle more!

I will be kicking back to a .5w zener real soon here.

Put in a .5w, 4.7v zener and measured the voltage - it clamps at 4.04v

*shakes head* Damn I hope the one I'm getting with my kit holds up and works right. Sorry to hear about all of your troubles everyone, but let it be known that all of us who are getting kits and planning on running the zener diodes very much appreciate your input on it.

Here's the weird thing - I ungrounded the diode trying to diagnose something, and I never see more than 4.8v coming off the MAP, even WOT at 5 lbs.

8Complex....HERE HERE....http://www.i-club.com/ubb-files/smilies/biggrin.gif

8Complex: what kind of boost fix is being supplied with your kit?

-Jon

Ok..I am totally confused now...But I went and bought 2 different ones from my local Electronic Supply...WHICH ONE Do I NEED to USE????Also the part numbers shown here are different from the ones you guys listed...Must be a Manufactoring Thing...These are from ECG componant

<IMG SRC="http://home.hawaii.rr.com/hiic/zener.jpg" border=0>

I am getting ready to do the install coming up...but I want to make sure I install the correct ones...The pkgs shown have 2 ea in them and they were $3...total...Let me know please...http://www.i-club.com/ubb-files/smilies/biggrin.gif..thanks

It's a marketing thing. They are cross-compatible parts to the 1N5230 and 1N4732.

You can find specs for each of them here, and you'll see that they match:
5009A: http://www.nteinc.com/Web_pgs/Half.html
5069A: http://www.nteinc.com/Web_pgs/One.html

Let us know how they work (or don't work).

-WaC
Wayne

I just received my 1N4688 samples. I have no idea how they will work, since no one local has a turbo MY00+ to try them on. Any progress from others?

-WaC
Wayne

Can somebody throw up a few pictures of your ECU with this in place?

I'd help you test, but I am still about two weeks away from getting everything installed.

-Jon

[EDIT] How did you go about getting the samples?

[This message has been edited by stimpy (edited April 18, 2001).]

pm'ed ya

stimpy - Zener diode. No clue on details though. :-/

So which one should I start with...I think I am going with the one watter first...anybody 2nd that????

Tomas...When I put it in I will shoot some pics...http://www.i-club.com/ubb-files/smilies/smile.gif

[This message has been edited by Scooby South (edited April 20, 2001).]

Some empirical testing here - the 1 watt 4.7v will cut below 4v - I think at 3.8 or so.

A .5w 4.7v will cut at 4.04.

A 1w 5.1v will cut at 4.3v - closer, and close enough until I get the .25w 4.7v to see how it works out.

PS - here is what I did to install if you aren't too sure you want to start soldering inside your ECU.

I used a vampire tap - Radio Shack nomenclature is Tap-In Squeeze Connector for 22-18 gauge wire - on the MAP wire, which is pink with a blue stripe. On the other side of the vampire tap is the lead that goes to the zener. I also used some 22-18 ga. snap connectors, so I can swap out the diode later.

I have about a 4 inch piece of wire from the vampire tap ending in a male snap connector, and a ground lead that uses a ring connector large enough to go over the mounting bolt for the ECU. The ground lead has a female snap connector.

Then I took the zener and soldered on a few inches of wire to each end, and put a female snap connector at the striped end of the diode, and a male on the other. Then I put heat shrink tubing over the diode and its soldered connections.

Now you can just plug the zener diode in between the leads. When I get the .25w diode, I will put it together the same way and replace the existing one.

Blaster: Try the 5.1V 400mW Zener. I've been running with it for roughly 2 weeks without any problems. WOT voltage is 4.72 and isn't cutting the injectors at all. If you can't find that one, try the 5.1V 500mW Zener - they're more popular afaik.

Good Luck! http://www.i-club.com/ubb-files/smilies/smile.gif

Rick - unable to track down a .4w 5.1 - I did order .5w 5.1s and 1w 5.6's to test.

However, that is now unneccessary. I received the .25w 4.7v zener diode (1N4688) from wac today and hooked it up. It clamps at <FONT COLOR="Red">4.79v</FONT c>. Woohoo! Perfect. And it pulls harder at the top end with it, too.

However, here is an important point - make sure all connections you use are securely soldered. If you look at the description of the installation I did above, all of the connectors are securely soldered, except for the vampire tap, which is secure enough in itself.

(My previous installation had some wiggle in some of the connectors, and it caused my ECU to freak on occasion.)

Of course the difference being that the purpose here is not to get around a factory safety design on a factory turbo car.

Of course a $2000+ programmable system provides more control and safety than than a dumb $.10 one.

But, interestingly, Rallispec acknowledges the drawbacks to this approach and says do it at one's own risk.

Finally, first post a lecture? Cool, perfesser.

The examples you state regarding Audi are, in no way, related to what is trying be accomplished here. You mentioned 'chips' with zener diodes to remove factory safety devices for a factory turbod car (in order to increase boost), but what we are doing is preventing a 1bar MAP sensor from sending invalid information to the ECU. Your examples are attempting to hack more fuel out of the ECU, we are simply trying to prevent the ECU from seeing information that it was never programmed to see. To accomodate for this, proper fueling measures are taken; whether we use RRFPR, fuel pump, FPR, AFC, ITC, or *insert fueling part here*, it all accomplishes the same thing.

Now what do you suppose J&S is putting in their FCD (voltage clamp) that sells for $150? Just your basic array of zener diodes and a little extra electronic wizardry. No black magic, just EE stuff.

-Jon

[This message has been edited by stimpy (edited April 24, 2001).]

I don't know... I would think that the J&S MAP Clamp would be a little more sophisticated. Probably an active voltage sensing circuit that outputs what it reads up to the voltage it is set for rather then an array of zener diodes.

All I have to say is that if I get my turbo and the zener diode doesn't work right, I'm gonna have a fit.

This is in response to blaster88 and stimpy:

How does fooling the ECU not get around a factory safety measure? If the ECU thinks you're running at a lower boost pressure than you actually are, you run the risk of not having enough fuel to safely run at the higher pressure. I would think that running software that has ignition and fuel maps for the specified boost level would be a much better and safer solution.

I admit I am not well versed in the specifics of the Subaru turbo engines, so I am unsure of what the best solution would be. The pressure sensor should be replaced by one with a higher capacity and the ECU software should be replaced with new software with the proper ignition and fuel maps for the higher boost pressures. If that requires a $2k programmable system, I guess that is the proper solution. I would have thought that someone offers chip tuning for the Impreza turbo. I know that Prodrive offers it for the Japanese and Euro-spec Imprezas, Legacys and Foresters.

As for TAP's Audi hack, there are no chips involved in the 10v I-5 "chip upgrade." All they do is install a resistor/zener mod and bypass all of the factory safeguards (incl. fuel cut-off, most importantly). No more fuel can be had than what is programmed for the stock max 1.4 bar (absolute) setting, as there are no ignition/fuel maps for anything above that. So rather than "attempting to hack more fuel out of the ECU," it is doing precisely what we're discussing here, which is fooling the ECU into thinking it is running at lower boost pressures and risking the possibility of grenading your engine from a lean condition.

Regardless of what has been posted in this thread- the resistor/zener mod is a hack. It is not the proper way to increase boost, and you run the risk of having many very unhappy WRX owners who try the mod, run out of fuel maps and grenade their relatively new engines.

This isn't so bad if you're starting off w/ a 15-yr. old, $1500 Audi 5000CS quattro with spare engines available for $500-600, but it is a heck of a lot more painful when it's a shiny new '02 WRX worth over $25k. Do you think the dealer is going to warrantee that grenaded motor?

I apologize for the long posts- you may object to my so-called "lectures," but my intent is to share information with the group- I have no delusions of superiority. Having researched boost mods for my Audis, I thought I'd share my experiences here, as I was concerned with this post. I've been lurking here on and off for a while, considering the purchase of a WRX. Rally Blue, of course- too bad I can't buy a P1 here in the States.

TM: you've missed a very important detail - this "hack" does not apply to the WRX, since the WRX doesn't use a MAP sensor.

The only applications this applies to are 2000 and 2001 N/A Subaru engines with aftermarket turbos and aftermarket fuel management systems. These owners/tuners are well aware of the risks.

-WaC
Wayne

WRX? We're talking aobout WRX's here? http://www.i-club.com/ubb-files/smilies/rolleyes.gif

Aha! There is the rub. Noone is talking about using a zener hack (it is indeed a hack, but hacks are most elegant when they are simple and they work) to increase boost out of a WRX - I am not sure that would even work.

The problem is that the MAP in a MY00 - MY01 RS is not built for boost at all. Seeing positive pressure in the manifold sends the MAP voltage out of range and then it just doesn't know what to do. Not so much a safety feature as the design of the system because it is an NA engine not truly designed to be turbo'd - which is why you have to get an aftermarket turbo in the first place. So the hack is to clamp off the map voltage to something it understands and handle additional fueling requirements through an uprated fuel pump and a fuel pressure riser that adds fuel in proportion to boost.

Yeah, Corky Bell says not to do it, that the "proper" way to any turbo is proper A/F management, but since there are no "chip" upgrades for the Subaru's (there is the JCSports Torque chip for $250 which noone is quite sure what it does, but certainly one of the things that it does is limit the MAP sensor voltage to its appropriate range, and it isn't what someone from the VW/Audi world would consider a chip upgrade because it is not a chip replacement but rather a wire-in black box), our choices are some parallel/piggy-back engine management system such as TEC II, Haltech, Motec, Wolf, or Link - and Link does make a full replacement ECU that is programmable. However, the price range on these devices is $1300 - $2500. Which is a chunk of change when you are paying $2k or better for the turbo system itself.

In that case, the argument might be, if you don't have 4 grand burning a hole in your pocket, forget about turboing your RS. That's a high hurdle, especially when you can really and for true get there without it. An RS running 5lbs of boost with the additional fuel requirements met and the MAP voltage clamped will indeed run with some margin of safety. Get into higher numbers and you are asking for trouble without more precise control. I think that is the lesson that can be taken away from shiv's work with folks through Vishnu Performance (though I am not speaking for shiv, he would probably say you should always have a TEC II http://www.i-club.com/ubb-files/smilies/smile.gif )

Is this hack enough for running 13 lbs of boost and turning 265 horses at the wheels? No. But it wasn't presented as such - Rallispec says good for about 6 lbs with additional fueling.

[ /lecture ]


[This message has been edited by blaster88 (edited April 24, 2001).]

Wayne, Blaster88:
My apologies- I thought we were talking about a WRX here. Quite obviously, I missed this very important detail.

Thanks for clearing this up.

Now what does the WRX engine management system use to determine what amount of boost is being produced?

BTW, how much boost is the WRX engine capable of before requiring the internals to be replaced, like the pistons, rods and crankshaft? With enough fuel, can they be made reliable at 24 psi?

TM

Andy et al.,
I can't believe you're advocating this kind of mod. The resistor/zener mod has been around for ages and it's just as bad now as it was then.

TAP made a ton of money selling "ECU chip mods" for Audi turbo quattros when all they really were doing was the resistor/zener mod. They have a bad rep because they've grenaded a few engines from this mod, disclaimed all responsibility, etc. It's a long story.

Anyway, the point is, don't do it. It's a hack way to get around safety measures that the factory put in for a reason. If you want more boost, get a proper chip mod from a reputable tuner (I'm not saying Rallispec is not a reputable tuner). This way you maintain proper air/fuel ratio so that you don't run lean and grenade your engine.

While I'm talking about I-5 Audi engines, the argument for proper chip tuning applies- grenading your engine from lack of proper fueling and high boost applies just as much to Scoobies.

If, regardless of my advice, you decide to go ahead and do the resistor/zener mod, please make certain that you have a fast-acting air/fuel meter and properly working knock sensors so that you can shut down the engine if it starts to ping.

TM

Probably a topic for another thread, but...

Someone correct me if I am wrong, but the same EJ20T in the WRX is running 280hp in the STi version of the car, and as I understand it the differences are in size of the turbo and intercooler, probably exhaust. No internals differences, though there is a 6-speed transmission which no doubt is stronger than the 5sp available in US models. If its making another 50 hp, it has to be running more boost. Stock WRX is 14lbs max, so 24 is not unlikely in the STi car.

Adding to Blaster88, I read that the STi engine spins to higher rpms. While the US WRX gets the same head, cams and adjustable whatchimadoohickie, the STi computer allows a higher rev limit.

Very mature thread.

silly question:

what is the difference between a one-way check valve and the voltage clamp?
I asked what the ASR turbo was using and the reply was: a one-way check valve. Is this better than a voltage clamp? Is it a more sound solution?

Cheers,

TSDScooby
-Emilio

A check valve works mechanically - evidently the MAP is connected by a tube to the manifold so that it reads manifold pressure. On a non-turbo car, it would only ever see vacuum or the highest pressure it could see would be atmospheric - 0 inches vac. A one way check valve would ensure that positive pressure can't make its way up the tube, thus causing it to send an out of range voltage to the ECU.

The diode works electrically, bleeding of excess voltage. The MAP can generate an out of range voltage, but it is clamped by the diode to a voltage in range.

Greg the STI engine is indeed different, especially the heads (valves/springs etc...)
and I don't think it was 24psi they were pushing, though I'm not 100% positive on that...

It should be noted that the zener diode option gives you approximately another 3 psi of headroom with which to add corrections with an S-AFC. The check valve effectively stops at 0 psi of boost.

Beyond these limits, you are relying on the FMU/RRFPR to do the fuel corrections. So you better be sure that your FMU is supplying enough fuel!

Of course, there should be a mechanical equivalent of a zener diode. And such a device is called a relief valve. I have no clue whether an affordable 3 psi relief valve even exists. The only examples I know of are also called wastegates and BOV's.

-WaC
Wayne

Edit: typos

[This message has been edited by wac (edited April 26, 2001).]

Thanks for the info. Some more comments and questions:

1. voltage clamp allows you to use electronic devices (e.g., SAFC) to tune the fuel requirements under boost.
On the other hand with a one-way valve, no signal pass 0 VAC comes from the MAP, so you can't intercept any value with electronics before going into the ECU.

2. The voltage clamps seems to be more intrusive (to install) than the one way check valve. Is it also less reliable?

Wayne, where does the exta 3 psi come from?

Given a scenario where you are running 5-7 psi, what are the disadvantages of tuning with a FMU vs. an SAFC?
Also, if you have a J&S to detect knocking, it will save you from breaking something when you don't have an SAFC to guarantee fuel requirements, right?

I'm just trying to get a good picture about this. It seems that this is the only "ugly" thing when turboing a MY00-MY01.

Thansk for the info folks.

Cheers,

TSDScooby
-Emilio

hey TSDScooby,
The 3 extra psi comes from the fact that the stock computer's fuel map can compensate for up to around 3 pounds of boost. So you want your voltage clap to limit the map senser voltage at 3psi which is at 4.7v. If you use a mechanical one way check valve then the map senser will only see up to 0psi any the voltage sent to the computer will be lower than 4.7v. Just like the diodes that were clamping to soon. Basicaly the voltage clamp lets you have more fuel injector duty befor you need to raise the fuel presure. hope this helps.

I guess all this extraneous info in this thread has distracted people.

In MY00-01 RS you must keep the ECU from seeing boost greater than about 3 lbs, or more accurately, from seeing a MAP voltage greater than 4.8v. If you do not, your ECU will freak out and the car will run like crap.

Whether you are running any other fuel management or not.

So if you have an RRFPR installed then there is no reason to do this right?

Additional options available at RadioShack if you can't track down a 1N4688:

A 1w 5.6v zener clamps at 4.76v - 1N4734B.

A .5w 5.1v zener clamps at 4.61v - 1N5231B.

Thanks again Blaster....your the man...

Well, I just got my 1N4688 from Wayne (thanks Wayne!). I've installed it using secure soldered connections (this is VERY important-the first time I tried it w/o soldering and the connecton came loose.).

Unfortunately, I don't have a way of measuring what voltage it's cutting at. But, what I do know is that my car pulls...and pulls HARD w/o fuel cut. It only cuts out for a very brief instant when I'm crusing in 5th and I floor it. I'm guessing it's partly due to the Vortech FMU delay. I'll do some more runs and post updates ASAP.

Thanks again wac!



[This message has been edited by Sauginius (edited April 28, 2001).]

Just a FYI:

The 5.1V 400mW Zener Diode 1N751B clamps at 4.72V.

It's been working fine for 3 weeks now, so I finally got off my lazy @ss, soldered it and bolted my ECU cover back on. http://www.i-club.com/ubb-files/smilies/biggrin.gif

Hey Wayne, ya coming up to MTL for a few Solo 2s?

Rick - where did you find that one? I was never able to track one down which is why I ended up with so many experimental models.

I just thought I'd throw my $.02 in. The Buick GN's MAP is a 3bar unit. I don't recall the PN, but The turbo Dodge guys have started to get away from the zener diodes and going with the GM MAPs. I hope this clears up some of the confusion. I'll add that no matter what you use to defeat the ECU or alter the signal it sees, you simply HAVE to have a way to monitor the A/F ratio, boost level, knock presence, etc...

wac / blaster88 / Stimpy -

What is your opinion of the 1N4732A? I went through the thread and couldn't find the exact clamping voltage, but this is rather a concern for me since all the Ludespeed turbo kits for the MY00 will be supplied with this zener diode. Ludespeed has reported that it has been working perfectly on it's test car, but hasn't provided any voltage readings at WOT.

8: the 1N4732A is less than ideal. Its zener characteristics do not work well for this application. Don't waste your time with either the 1N4732A or the 1N5230A - others have reported problems with both of these. (Can't you read through this thread? http://www.i-club.com/ubb-files/smilies/rolleyes.gif )

Ingo (Rick Hunter) had good success with a 1N751B. Therefore, I'd suggest using either a 1N4688 or 1N751A or 1N751B. Someone should also try a 1N5231B, as it should be similar to the 1N751B, and may be easier to obtain.

Ingo: yes, I'm planning on a visit to SANAIR July 29. I hope my coupon from last season will work. The wagon is running much better now with the EJ25 injectors.

-WaC
Wayne

Edit: UBB code

[This message has been edited by wac (edited April 29, 2001).]

wac - you musta missed my post - I tried a 1N5231 (.5w 5.1v) and found it to clamp at 4.61v.

8 - the 1N4732 (1w 4.7) will work (sometimes) because it will clamp below 4.8 - I think in Rick Hunter's case it was 3.4, I saw 3.8. However, using one of the other alternatives will get much closer to 4.8, and trust me, it will pull MUCH harder with the higher MAP voltage.

Storm - I think it was in this thread but replacing the MAP won't do the trick because it will not provide the proper voltage in non-boost conditions.

blaster: Thanks, bud. I did miss that one. (LOL, looks like I should have followed my own advice and looked for it in this thread. http://www.i-club.com/ubb-files/smilies/rolleyes.gif )

The 1N5231A then, will work better than the 1N4732A and 1N5230A, but it won't be ideal.

-WaC
Wayne

Blaster: heh I mentioned where to find the 1N751B 5.1V 400mW above - ya must have missed my post too. Seems like the size of this thread is affecting everyone. http://www.i-club.com/ubb-files/smilies/biggrin.gif

/cut&paste
I searched a whole lot of local electronics shops here in Montreal and only one (Abra Electronics 514-731-0117) had the 5.1V 400mW 1N751B.
/!cut&paste


Wayne: Great! Your coupon should work, you earned it after all http://www.i-club.com/ubb-files/smilies/smile.gif Jimmy upgraded his suspension to the GC setup & is getting Toyo RA-1s. Looks like it'll be a competitive season. I'm slowly getting setup for the start of the seaon - tires and hopefully suspension. I wonder how many more cones I'll kill this time...

Why not buy a torque chip from me and save yourselves the trouble ;)

Larry
www.ImprezaRS.com

Any any more update on these zener diode? I'm now looking into the 3 zener diode.

1N751B clamps at 4.72V
1N4688 clamps at 4.79V
1N4734B clamps at 4.76V

Does anyone have problem with the 1N4688 one? I'm thinking the highest voltage without setting the CEL light/fuel cut will be the best.

Thanks

Can the Forum mod please move this to the aftermarket turbo forum? Thanks!

This is not an advertisement. About two weeks ago I tried the 4.7V 50mw zener diode and watched it on the OBDII.

Compared to my torque chip which clamps pressure at 32 inches of mercury, the diode allowed my barometric pressure to spike to 34.7 inches of mercury triggering a high ABS Manifold presure CE light. After a few seconds under boost the pressure would bleed down to 27 inches of mercury and I would run lean, with EGT's normally 1450 going to 1600. I had to crank the dual throttle body injectors up a lot to get EGT's back down to normal.

Since the MAP sensor isn't designed to drive a load, I decided not to test other wattage Zener diodes for the time being. Just seems to me they can overshoot, or not hold the MAP voltage steady.

I do plan to start testing the prototype www.proECM.com ajustable voltage clamp soon, which not only will allow you to run over 203 psi of boost on a 2000-2002 model, but will let you remove the high boost fuel cut on a WRX. So far testing of their fixed voltage clamp shows rock steady MAP values, similar to the torque chip.

Now there is content here to pertain to the WRX ;)

Take care,

Larry

I ran into a MAF limit recently on my 14psi Mazda MP3 (which wasn't boosted from the factory).

I have a piggyback system as well as an additional MAP sensor that the piggyback reads. I'm pretty sure the max limit is 4.8v as well.

Just wondering...will this trick work?

And how exactly do I test what voltage is being attained?

Can I just cut into the wires coming out of the MAF under the hood instead of playing with the ECU?

How do you guys secure the diode so that it does not break?

Can the Forum mod please move this to the aftermarket turbo forum? Thanks!
Well, it took me 3 years, but I finally got to it. :lol:

No ninja points for you, Nick ;).

OMFG. When I read this title, I thought there was finally a cure for the low MAP voltage CEL. :( :mad:

:lol:

-Brett