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Old 08-27-2001, 07:41 PM   #1
yebokmj
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Default Stalling Problems with MY98 RS Turbo

I have a MY98 RS running the HKS Super AFR for fuel management, along with an upgraded fuel pump and a fuel pressure riser. I have had a slight problem in the past with my car stalling but very rarely. I recently installed a lightened flywheel and it has become more consistant. It generally happens when coming down from revs with the clutch in, or in netural. I have heard that this is a common problem with MY98 and previous year cars, I once heard it has to do with the air control valve that other years don't have. Anyone have a solution?
Thanks,
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Old 08-27-2001, 10:14 PM   #2
tom@kartboy
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i believe the problem is from the lightened flywheel. you loose all the inertia. that the heavier one had. you might be able to cheat it by bumping the idle up a touch
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Old 08-27-2001, 10:31 PM   #3
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I believe that Tom is right on that one. the light flywheel will only excerbate any idle stalling problems. in fact on some stock vehicles it supposedly can stall.
are you showing any signs of running rich at idle? if so that could lead to stalling (I think). Perhaps adjust the off boost settings on the FPR to run leaner at idle.

good luck
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Old 08-27-2001, 10:40 PM   #4
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I believe that Tom is right on that one. the light flywheel will only excerbate any idle stalling problems. in fact on some stock vehicles it supposedly can stall.
are you showing any signs of running rich at idle? if so that could lead to stalling (I think). Perhaps adjust the off boost settings on the FPR to run leaner at idle.

good luck
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Old 08-27-2001, 11:40 PM   #5
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Hey Josh, I have the same problem (or did before my MAF blew ) anyways someone told me its cause to high fuel pressure at idle. No matter what I did with my AFR it wouldn't help it out, I even switched back to the stock fuel pump and that didn't help either. I also didn't have a Fuel Pressure Riser either.

Also I had the problem although not as bad before I put the flywheel in too.
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Old 08-28-2001, 12:15 AM   #6
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Default Tried that

I have already tried leaning it out at idle it helped a little, along with uping the response. But it still does it. I guess I just have to be more careful with how I let the revs fall. Any other suggestions would be apprecited.
Thanks,
Joshua
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Old 08-28-2001, 12:55 AM   #7
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If you're indeed stalling at idle due to abnormally high fuel pressure (due to the higher flow pump overwhelming the stock FPR, exacerbated now by the lighter flywheel), then you may want to find an SVX FPR to replace yours. The idle fuel pressure should return to normal, and this may make your stalling problem go away.

(This info courtesy of 8Complex, who posted in response to an earlier thread of mine asking about fuel pressures after high-flow fuel pump install)
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Old 08-28-2001, 01:28 AM   #8
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Joshua,

I'm running the same setup as you (MY98 RS-T), including lightened flywheel (14.9).

I don't have a Fuel computer or any electronics for that matter. The Only thing I've done is made my fuel rails run in parallel, swapped the stock FPR for a Weapon-R FPR, and I'm currently running my stock injectors. I'm set at 7psi right now and everything runs Perfectly and Safe. I usually run 8-10psi when I have my 370cc injectors in.

Anyways, about the stalling. Are you pushing the clutch in at fairly high RPM's (above 3000) when you're coasting to a stop? If so, the engine RPM will drop so fast that the Idle Air Solenoid (IAS)can't adjust fast enough. This has happened to me, but I've found that if you down shift and push the clutch in around 1500 RPM or so, that it won't do it. Sometimes you can watch your Tach, it probably drops to 500 or below and then comes back, that's the IAS reacting a little slowly. You're ECU is probably a little confused. Usually, after a while it will learn where to idle, then it knows when it has to open sooner to prevent the RPM drop. Mine has done this, then after a while it straightened itself out.

Most of all, just don't push the clutch in after say taching-out 2nd and coast to a stop! It will always stall!

Just my $.02
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Old 08-28-2001, 01:38 AM   #9
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Quote:
Originally posted by mcgyver
Sometimes you can watch your Tach, it probably drops to 500 or below and then comes back, that's the IAS reacting a little slowly
-Adam
the IAC solenoid does not do that, cars without them do this also, I know because I removed mine...
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Old 08-28-2001, 01:53 AM   #10
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I would keep my eye on your MAF sensor..........
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Old 08-28-2001, 01:54 AM   #11
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Or your eye
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Old 08-28-2001, 11:29 AM   #12
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Mine does that if I let my BOV vent into the air. Check for leaks. I have an extra 93 MAF

Chad
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Old 08-28-2001, 04:49 PM   #13
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What is your idle fuel pressure? Very likely it is too high and causes the engine to stall like that. As the Dabbler said above, I used an FPR out of a junkyard SVX to fix mine (original info courtesy Al Gainey (ARG)).

I didn't have troubles with mine when the fuel pressure was around 44psi at idle, though I knew from previous experience, the ECU wants the fuel pressure about 33-34psi at idle. After I installed the SVX FPR it lowered back down to about 31-32psi at idle and it runs great.

EDIT - subachad just reminded me... I had read a while back that venting to atmosphere caused the engine to run rich for a second if you have a MAF sensor. Reason being, it accounts for that air already and adds fuel accordingly, but it vents the air out, leaving the motor just adding fuel.

Here is a trial for you to tell which is causing your problems - get your rev's up high, but hold it there a second and watch your boost gauge so that you only release it when you're under vacuum or 0 boost (preferably vacuum). When you release it, if there is vacuum and it still stalls, it is probably your BOV, if it doesn't and is consistent, most likely it's your fuel pressure. Note - I just thought of this test, so I'm not 100% since I haven't tested it, but it just makes sense, I believe.
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Old 08-28-2001, 04:58 PM   #14
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ok I went along with this theory, when I orgianlly posted the same problem, but I've been thinking about this all night and I don't believe high fuel pressure is the problem....maybe part of the problem.

Because I have a turbo kit (same as yebokmj), sort of a test I swaped the stock fuel pump in, NO RRFPR, and no fuel addition using the AFR, and I could still stall the car at stock fuel pressure levels...33psi.

Explain why

EDIT - 8complex - The HKS Super-AFR works with BOV's and can learn the rich conditions created by it and can lean it out when this happens.
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Old 08-29-2001, 12:37 AM   #15
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Lightbulb

The problem is the ECU and the Idle Air Control Motor. I have thoroughly researched this problem for the past year and a half, because I have a 98 with a turbo and a light flywheel. Basically, the ECU is too slow to respond (the ECU is fast at processing info, but due to some programming reason, the response is slow with this particular aspect of engine management.) Here is what happens: When you release the throttle, the engine senses the rapid decrease in throttle position, and then looks for an increase in vacuum. When the engine RPM lowers to a predesignated value, it actuates the IAC motor to maintain RPM around 700. The predesignated value for response seems to be below 700. I have analyzed the signal to the IAC motor with a meter, and have found that essentially the signal is not sent to actuate IAC motor until it is too late. With the light flywheel, the engine simply revs down far too quickly than was intended by Subaru's engineers. At the same time because of the turbo, there is so much air and fuel being consumed by the engine, that sudden releasing of the throttle will cause a momentary rich fuel condition until the injectors respond appropriately, and the rich air fuel mixture is purged through the exhaust ports. I have a theory that Subaru engineers intentionally created this "pause" period during closed throttle so that the brake system could recharge on vacuum. By keeping the IAC motor shut at closed throttle and high RPM, a generous amount of vacuum is being generated for the brake vacuum canister. Additionally, many hard braking situations are created after rapid releasing of the throttle (i.e. rock or deer in the road, etc)

Here's a little experiment which illustrates everything clearly(MY 98 turbo's only): Drive full throttle until 6000 RPM. As soon as 6000 RPM is achieved, simultaneously depress the clutch and release the throttle as quickly as possible, so that engine speed can freely decrease. More than likely, engine stall will occur. In a second scenario, once again, accelerate to 6000 RPM at full throttle. This time however, when you reach 6000 RPM, only release the accelerator pedal and do not yet engage the clutch (this part of the experiment works best in 4th or 5th gear). Wait a few seconds for the IAC motor to activate, and then push in the clutch and let engine speed freely decrease. You should find that the ECU will be able to accordingly control idle speed without engine stall.

Furthermore, raising the idle speed with the set screw on the throttle body will not help much unless your idle is about 1100 RPM. In such case, your Check Engine Light comes on if a sustained idle RPM over 799 is achieved.

Also, readjusting the Throttle Position Sensor so that high throttle condition is anticipated at a different than actual point by the ECU does not help much either after a certain point. The ECU usually anticipates high throttle at a little more than half throttle. If you turn FORWARD the TPS so that this point is actually anticpated at something like 3/4 throttle, you will be able to stave off the stalling condition a little better. Basically, the ECU detects a departure from high throttle condition sooner, and the timer on actuating the IAC motor starts sooner, so therefore you have more time before the engine reaches its critical point. However, engine smoothness and throttle response is comprimised due to the transition between open loop and closed loop fuel management based on throttle position. If you don't understand this, try it and you'll see exactly what I mean. On the other end of the spectrum, if you adjust the TPS BACK, the ECU will not detect departure from high throttle condition until something like 25% throttle, and thus the ECU has even less time to respond, and ultimately stall conditions are worse.

Furthermore, experiments with the manifold and atmosphere pressure sensor solenoids, FPR, and adjustments to the IAC motor have unsuccesfully produced any solutions, yet have however illuminated proof to the aforementioned theory.

Please feel free to unabashedly criticize my analysis.
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Old 08-29-2001, 02:32 AM   #16
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xephyr - Great theory! But one question... how does it sense manifold pressure if there is no MAP sensor? Or does it have one and just use it as a backup/check for the ECU only?
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Old 08-29-2001, 07:26 AM   #17
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The MY98 does have a MAP sensor (which will throw a code for high manifold pressure when boosted).

And wow, xephyr, looks like you've put a lot of work into researching this. I "had" a problem along these same lines after turbocharging my MY98, but I've messed with my S-AFC decel function enough to keep it from being a problem. The S-AFC instructions for setting the decel function are difficult to understand, so I just tried different settings until something seemed to work. It's been quite a while since my car has stalled.

Also, I doubt that venting BOV to atmosphere on a MAF is any worse than venting it back into the intake. I've been running my BOV to atmosphere for most of the summer without any problems. (Well, my car backfires often, but it does that either way. )

Steve
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Old 08-29-2001, 01:50 PM   #18
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Question Always signaling?

What if you where to have a signal always going to the IAC so that it was always on? What problems would that cause? Would it solve the problem at all? xephyr thanks for all your info.
Joshua
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Old 08-29-2001, 01:58 PM   #19
yebokmj
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Question Always signaling?

What if you where to have a signal always going to the IAC so that it was always on? What problems would that cause? Would it solve the problem at all? xephyr thanks for all your info.
Joshua
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Old 08-29-2001, 03:28 PM   #20
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Default Re: Always signaling?

Quote:
Originally posted by yebokmj
What if you where to have a signal always going to the IAC so that it was always on? What problems would that cause? Would it solve the problem at all? xephyr thanks for all your info.
Joshua
Joshua,

You can't just keep the IAC motor on all the time. That would open up the throttle body completely and your engine would effectively be at full throttle. What you need is better/faster control of the motor.

-Edwin
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Old 08-29-2001, 04:02 PM   #21
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Default Re: Re: Always signaling?

Quote:
Originally posted by efoo


Joshua,

You can't just keep the IAC motor on all the time. That would open up the throttle body completely and your engine would effectively be at full throttle. What you need is better/faster control of the motor.

-Edwin
the IAC on our cars do not touch the butterfly, they have their own passage that they use to allow air into the intake manifold, although I wouldnt give it a full signal the whole time I would think about giving it a partial signal if possible?
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Old 08-29-2001, 04:05 PM   #22
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You can definitely achieve a stall-free MY98 Turbo with proper engine management. I had a stalling problem (made worse by having 550cc injectors), but with a good TEC2 engine map I achieved stall-free performance.

Unfortunately, a month or two ago I made a change to my engine map that made on-off throttle transitions very smooth BUT that same change also brought back the stalling problem. I now stall occasionally if I go into neutral after from a high RPM. A quick blip of the throttle before bottoming-out keeps the engine alive, though.

I think I can get it back to stall-free -- it's just a matter of proper tuning.
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Old 08-29-2001, 04:49 PM   #23
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Steve is right 8, any car that has a MAF should have a MAP sensor as well. What we call "MAP equipped" cars have only that for air flow calculations.
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Old 08-29-2001, 08:13 PM   #24
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Default no more stalling with S-AFC; sort of

I had a stalling problem with my 2.2 turbo until i got the S-AFC. I agree with SteveS the instructions suck. I still dont understand what the decel function does. I set the NE1 point to 1.3% and the NE2 to .9% this eliminated the stalling after reving the car when warm but it still stalls when its first started up. i think it has to do with the idle being set higher at startup, so i just shut off the decel function until the car is warm. If anyone has had better luck with setting up the SAFC please let me know.
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Old 08-29-2001, 10:37 PM   #25
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Default IAC motor moification

Re-wiring your IAC motor so that it is partially or fully on would create a high idle condition for the ECU. Also, on some turbo kits, the IAC motor vents to the intake between the turbo and air filter, so therefore any boost built in the manifold would be vented out and you would ultimately have trouble building any boost.

One option would be to essentially create an electrical device which senses throttle position and accordingly actuates the IAC motor. I have considered this option, but have decided that attentive throttle management with my foot is much easier than designing such a device. Another option would be to create a small mechanical dampener which one could attach to the throttle body (almost like a little shock absorber). This dampener would have to prevent the throttle body butterfly from fully closing initially, and then slowly allow the butterfly to close after a few moments.

I have also tried to adjust the decel function on my S-AFC without any success. I drive from the mountains in Vail to Denver on a regular basis, and I have found that the different altitudes change the required settings to prevent stalling. Basically, if I tune the S-AFC decel function to prevent stall in Denver, it works only in Denver but not in the mountains, and vice versa.
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