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Old 07-03-2002, 09:58 AM   #1
mdot
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Default Using stock EGT probe?

I did a search and learned a little from the first 60 of 553 posts. But it raised more questions.

I got the new probe with my guage, and i understand where and why people are locating it. I have the abuility and time to do it, but why, if we can use the stock senser or at least it's location?

The posts i read said, the stock probe may be crap and/or incompatable with my autometer guage. If that's the case, I know what i need to do.

They also said the stock probe can be removed and replaced with a resister (2k ohms i beleive) at the ecu, leaving the stock location open for the new probe. Why can this be done, does not the ecu need this information?

before anyone says that i must put my probe in the "hot #3 cyclinder manifold". think about this: even if the temp is cooler in the stock location, i can still use my guage and see when i'm running hot. the trend is more important to me than the exact temp number (that will probably not be actuall anyway do to low cost parts) when i see my guage climbing above average, i will take notice and reduce whatever i'm doing to cause it.
but anyway...didn't mean to rant...

so: why can or can't i use the stock probe?
If i can use the stock probe, can i just tape into the wire, or do i have to disconect it from the ecu?
if i have to disconnect it from the ecu, why does that resister do the job?
if the resister mod is valid, is there a reason i can't use the stock location for my new probe?

thanks guys.
mdot
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Old 07-03-2002, 01:51 PM   #2
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bump

no advice? bad or good?
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Old 07-03-2002, 02:18 PM   #3
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from my understading

the stock probe is tooo slow to use

the 2.2kohm resister will work .. you get somthing like this with the perrin up pipe

assuming the the stock egt uses 1/8 npt .. yeah it should screw right in.

note: vishnu uppipe has a second bung in it for an aftermarket egt sendor
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Old 07-03-2002, 04:59 PM   #4
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You can use the stock egt location in the uppipe.

You will get data from all cylinders doing this, but the data will be less accurate (temperature drop over time/distance and mixing of exhaust from different cylinders).

You should decide what you want:
more accurate data from one or two cylinders
less accurate data from all cylinders

Both have advantages and disadvantages.
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Old 07-03-2002, 05:59 PM   #5
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accuracy might be lower, but not precision. like i said, trends are what more people look for than numbers. if i notice my egt is 100 degrees hotter than average, it doesn't matter if it's a 100 degs hotter than 1400 degs or 1500 degs. i know i need to slow down.
(if i really wanted to i could reposition the needle to read higher, therefor more close to actuall, but this is all besides the point)


Can I replace the stock probe with my new probe, and have the ecu and my guage both read that new probe?
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Old 07-03-2002, 08:24 PM   #6
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good question i know what your saying about the temp readings i've been woudering the same thing about where to put the probe the stock place sounds good to me. i think i will do it. a lot eaiser than drilling in to the manifold.if subaru thinks its a good enough place then why not,they are the ones who built the engine.
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Old 07-03-2002, 08:36 PM   #7
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Wink Mdot

I'd have to agree on this one with you. It's the trend in temperature you're concerned with. What you really need is someone with heavy mods who has put thiers in this location say " the highest I've seen is xxxxx deg at WOT" for a baseline. That would help tremendously. You'll obviously build your own mental database of temps over time, too. But to get an idea of what to expect before doing so would certainly be nice as well.

I asked the same question, to a degree (no pun intended,) in this thread http://forums.nasioc.com/forums/show...hreadid=207155 of which you've prob. already read. I came to the conclusion that I'm not touching my passenger side manifold again unless absolutely necc. The basline numbers were all I was looking for in this particular mounting location. I got what I wanted too, and see just about the same readings as those who've mounted on the other side of the engine!

To answer your question if the ECU / your gauge will read the new probe simutaneously, I doubt it. I'd stick with doing the 2.2k ohm resistor mod in the factory EGT probe connector, and rely on using your gauge to see what's going on. If I'm not mistaken, doing the resistor mod just "fools" the ECU into seeing a constant 1400 deg. F reading from the now missing OE probe. JMO

HTH - Jim

Edit: to the 3rd paragraph, another reason to do the resistor mod. If you don't hack up the OE probe connector, and decide that you don't like the new probe in this location, you'll have an easy way to put things "back to normal" at that location (as far as the OE equipment goes.) Just something to think about......

Last edited by MackDaddy; 07-03-2002 at 08:46 PM.
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Old 07-03-2002, 08:49 PM   #8
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does anyone really know why there is a egt probe from the factory what is the ecu doing with this info and if you do the resistor mod what are you taking away from the ecu? Is this really a safe idea? I've done some reading on this as well but couldn't find a concrete answer other than speculation. I would think they have a egt there for some reason other than a p[lace to put an aftermarket gauge.
-James
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Old 07-03-2002, 08:56 PM   #9
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Default From what I uniderstand

Quote:
Originally posted by jjunior887
does anyone really know why there is a egt probe from the factory what is the ecu doing with this info and if you do the resistor mod what are you taking away from the ecu? Is this really a safe idea? I've done some reading on this as well but couldn't find a concrete answer other than speculation. I would think they have a egt there for some reason other than a p[lace to put an aftermarket gauge.
-James
It's there to keep track of EGT's, just like we are. But the ECU will adjust fuel / and timing to cool things down if it's see's readings too hot ("hot" as far as it's concerned, is still a mystery to me.) I'd have to agree with leaving it in place, as the ECU is still doing it's job (for safety reason.) I wanted to try this location as Mdot is contemplating, but decided to do my probe elsewhere, and keep the factory sensor in place so the ECU has control over what it see's from that location.

In his situation though, I'd try what I stated above. Log some data, drive the car like I had some sense, and evaluate what I saw. If I got paranoid, or changed my mind for any reason, The stock components could easily be put back in place.

Jim
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Old 07-04-2002, 11:16 AM   #10
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Default Re: From what I uniderstand

Quote:
Originally posted by MackDaddy
It's there to keep track of EGT's, just like we are. But the ECU will adjust fuel / and timing to cool things down if it's see's readings too hot ...
The thermocouples used with aftermarket EGT gauges generate a voltage that rises with temperature. The stock EGT sensor is a platinum film RTD (Resistive Temperature Detector) sensor whose "signal" is its resistance, which falls as temperature rises. Such sensors have a linear response up to around 1000C with an accuracy of +/- a couple percent and have a response time of about a half a second. In other words, the stock EGT sensor is both fast and accurate, but unusable with typical aftermarket EGT meters.

The stock EGT sensor was introduced along with the precat. It's only purpose is to allow the ECU to protect the precat from excessive EGTs which might damage the precat (the precat has a Federal Emissions warranty for 8 years / 80,000 miles). Unless you consider "limp mode" of not running at all to be the ECU adjusting "fuel / and timing to cool things down," the initial quote, above, just isn't true.
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Old 07-04-2002, 11:33 AM   #11
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Default I stand corrected

Quote:
Originally posted by Cocoa Beach Bum
The thermocouples used with aftermarket EGT gauges generate a voltage that rises with temperature. The stock EGT sensor is a platinum film RTD (Resistive Temperature Detector) sensor whose "signal" is its resistance, which falls as temperature rises. Such sensors have a linear response up to around 1000C with an accuracy of +/- a couple percent and have a response time of about a half a second. In other words, the stock EGT sensor is both fast and accurate, but unusable with typical aftermarket EGT meters.

The stock EGT sensor was introduced along with the precat. It's only purpose is to allow the ECU to protect the precat from excessive EGTs which might damage the precat (the precat has a Federal Emissions warranty for 8 years / 80,000 miles). Unless you consider "limp mode" of not running at all to be the ECU adjusting "fuel / and timing to cool things down," the initial quote, above, just isn't true.
Obviously, you know more than I do on this subject. Insight much appreciated.

Jim
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Old 07-04-2002, 11:42 AM   #12
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Lots of good info thanks guys-James
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Old 07-04-2002, 01:08 PM   #13
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Quote:
Originally posted by mdot
accuracy might be lower, but not precision. like i said, trends are what more people look for than numbers. if i notice my egt is 100 degrees hotter than average, it doesn't matter if it's a 100 degs hotter than 1400 degs or 1500 degs. i know i need to slow down.
(if i really wanted to i could reposition the needle to read higher, therefor more close to actuall, but this is all besides the point)


Can I replace the stock probe with my new probe, and have the ecu and my guage both read that new probe?
You are making the same argument that I made months ago. I see that great minds think alike...

As CBB wrote, the stock probe is not a thermocouple, so you cannot use it with an off the shelf aftermarket gauge.
The resistor makes the ECU think that the EGTs are at a constant temperature within an acceptable range so there is no CEL.
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Old 07-05-2002, 08:57 AM   #14
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thanks guys, (special thanks to mackdaddy, cocoa, and qa)
I really appreciate the info/input.
i think I'll do the resister mod, the put the stock back in when i get the VS0.
now, just to find time...
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Old 07-05-2002, 10:22 AM   #15
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Default Re: Re: From what I uniderstand

Quote:
Originally posted by Cocoa Beach Bum
TThe stock EGT sensor is a platinum film RTD (Resistive Temperature Detector) sensor whose "signal" is its resistance, which falls as temperature rises. Such sensors have a linear response up to around 1000C with an accuracy of +/- a couple percent and have a response time of about a half a second. In other words, the stock EGT sensor is both fast and accurate, but unusable with typical aftermarket EGT meters.

Unfortunately, I think you are wrong on this subject. The stock sensor not only is VERY nonlinear, it is also VERRRY slow in response. I have measured the resistance of the stock probe vs temperature against a digital type K thermocouple, and the readings are basically useless below 1000F. The reponse time is terrible; 100-200 degrees per SECOND if I recall, which makes it useless for seeing peak temperatures as you "row" through the gears. Those who have the Delta Dash software can verify this. The sensor is, however, very accurate and sensitive(not reponsive) in the temperature range of 1400-1600F, where the ECU is looking for high EGT problems.

Mark
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Old 07-05-2002, 08:45 PM   #16
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My dd readings showed the stock egt to be very sensitive and responsive. However, at idle and cruise it seems to register too low. Once at wot, the temps will climb to 1425 on my car. Funy thing, though. After logging for a month now the sensor readings are no longer accurate. It seems slow to respond AND inaccurate. I am not sure why. This may explain why some claim they are terrible while others see them as very useful to read.

I might as well do the resisitor mod now. Do you just cut the two wires that go to the sensore and wire the 2.2k ohn resistor in between the wires?

Greg
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Old 07-05-2002, 09:30 PM   #17
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Quote:
Originally posted by TurboRex
My dd readings showed the stock egt to be very sensitive and responsive. However, at idle and cruise it seems to register too low. Once at wot, the temps will climb to 1425 on my car. Funy thing, though. After logging for a month now the sensor readings are no longer accurate. It seems slow to respond AND inaccurate. I am not sure why. This may explain why some claim they are terrible while others see them as very useful to read.

I might as well do the resisitor mod now. Do you just cut the two wires that go to the sensore and wire the 2.2k ohn resistor in between the wires?

Greg

Greg. Get an M12X125 mm bolt from the hardware store along with a nut. Stop by radioshack and get a 2.2k 1/4 watt resistor.

Unscrew the sensor from the upippe. Thread the nut onto the bolt. Thread the bolt into the uppipe a bit 1/2 inch or so... Then tighten the nut down agains the uppipe. There. it will NEVER rattle lose now.

Unhook the EGT probe connector under the small access panel by the boost solenoid. Take the resistor. Cut the legs down a bit. Fold it over and stick it in the car side of the plug (car is female). Wrap tape and or heat shrink over the connector.

Done.. Now it cant fall off and slam into your 100,000 rpm turbo. Delta Dash reads 690C all the time. I have yet to experiment with values. I want to.. I know people say that its to monitor the precat but I would suggest that might not be the case. After all... How do they know...

CT
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Old 07-08-2002, 04:49 AM   #18
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Default Is it A or B?

A. Stock EGT sensor saves precat. Resistor mod keeps ECU happy.

B. Stock EGT sensor protects ALL cats (and other engine parts) from meltdown. It also uses data to adjust fuel, timing, and whatnot.
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Old 07-08-2002, 06:09 PM   #19
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bumpity-bump

good question: a or b?
especially the part about whether the ecu changes fuel/time/etcetera with EGT changes?

az scoobie,
you called out a metric bolt, which makes sence being a japaneze car and all, so i take it my 1/8 NPT probe won't just screw right in?
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Old 07-08-2002, 06:27 PM   #20
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Bump again.

I would much rather use the stock location with the resistor mod than have to remove the manifold, drill, and tap. Assuming my probe will fit my Vishnu uppipe. I too am more concerned about trends than exact numbers at one cylinder.

So is it A or B?

Padre
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Old 07-08-2002, 06:36 PM   #21
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If you were to attach an aftermarket meter to stock probe you would need to make sure that the resistance range of stock probe matches what the aftermarket meter is looking for. For example if an optimum resistance for the stock probe/thermistor reading is 2.2K ohms with a range of 2000 ohms(this is not true but for example purposes) the aftermarket meter must be calibrated to accept a range of 2000 ohms. If the aftermarket meter is matched in range to factory probe but does not match in value you could put a resistor inline with the aftermarket meter to match the calibration, assuming that meter is reading to high of a voltage because of low resistance.
I would also think that wiring the meter up in parralel with the stock system would not harm the voltage that thermistor is putting out. It would just lower the current since both the ecu and meter are both reading off the same probe.

If this can happen it would definitely same me and everyone else time, money, and headaches. Especially if we are just looking for trends off the normal values. Personally I do not care what the exact value is, I just want to know if increase the boost around how much higher are my EGT's reading.

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Old 07-08-2002, 07:52 PM   #22
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raptor5,
At least 2 i-Club members have measured the resistance of the stock EGT sensor at various temperatures. WRX216 published his measurements in thread http://forums.nasioc.com/forums/show...readid=126396. fastburro has also conducted what appear to be very precise measurements (see http://forums.nasioc.com/forums/show...hreadid=149428), but has so far avoided publishing his results. It's probably because he had ambitions of producing the ultimate WRX meter using the stock sensors (see http://forums.nasioc.com/forums/show...hreadid=117202). But, maybe since he was the first i-Club adopter of the ECUTEK DeltaDash, he has abandoned this project and is now willing to share his data.

I'll leave it to you, raptor5, to coordinate the design of the stock EGT sensor meter.
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Old 07-08-2002, 07:54 PM   #23
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Default Re: Is it A or B?

I almost forgot.
Quote:
Originally posted by aspera
A. Stock EGT sensor saves precat. Resistor mod keeps ECU happy.

B. Stock EGT sensor protects ALL cats (and other engine parts) from meltdown. It also uses data to adjust fuel, timing, and whatnot.
I vote A.
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Old 07-08-2002, 09:10 PM   #24
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Quote:
Originally posted by mdot
bumpity-bump

good question: a or b?
especially the part about whether the ecu changes fuel/time/etcetera with EGT changes?

az scoobie,
you called out a metric bolt, which makes sence being a japaneze car and all, so i take it my 1/8 NPT probe won't just screw right in?

Nope. Sorry.. You will need an M12 X 125 thread bolt.


CT
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Old 07-09-2002, 03:12 AM   #25
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C. Stock EGT serves no purpose at all except to distract us while sneaky Subaru dealers creep up to our cars and copy our VIN numbers so that they can void our warranties on everything we own or will own (including L.L. Bean clothing sold at Subaru dealerships).

D. boobs
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