Lightened Flywheel cause my stalling?

[Ludachris]

Hey guys, I just put a new motor in the car with a MAFT and a bunch of other new goodies (listed in my profile). The problem is the car keeps stalling when I rev it, or when I come to a stop sign and push the clutch in. If I don't downshift all the way to 1st gear to ease the car down to idle, it dies. I've checked the ISC, the BISS, done a pressure test, and have done some initial low end tuning. I've been told that the ECU can't compensate correctly for a lightened flywheel. The revs drop faster than the ECU is used to and it can't catch it in time before it stalls... that makes sense, but then again, wouldn't that prevent the entire DSM community from using them?

Anyone else running a lightened flywheel with a similar mod list as me and having a similar problem? Is there anything else I should check before I pull the tranny again? How is it that so many others are able to use lightened flywheels without stalling?

 

[steve]

Chris,

There may be issues with the ECU dashpot emulation and light flywheels but it also tries to keep the idle speed up when the car is moving. Can you check and make sure your speed sensor is working?

If your using MMCd try logging 0xC6 on the custom sensors page.

Steve

 

[MNGSX]

It could be...

I dont think I'd blame the fly but the ECU... Light = good so maybe the keydriver ppl will have a fix for you..

It has happened to people with similar modified ECU's and stock ecus.. The pro-efi did'nt do it.. Although my 2g when it was on MAFT alone does'nt do it unless its a wide RPM drop fast.. Little drops fast like you are talking about no. Like going from WOT high rpm to cruise/Idle then It will do it.

 

[steve]

Light = good so maybe the keydriver ppl will have a fix for you..

I know Jeff was looking for some help last week locating the code that does the dashpot emulation. I don't know if he's found it. I'm getting closer to finding it but a lot of the code depends on state variables we haven't mapped out yet.

Steve

 

[diambo4life]

How about using the BISS to raise the idle RPM?

 

[99gst_racer]

How is it that so many others are able to use lightened flywheels without stalling?

I had to raise my idle after I installed my lightweight flywheel. If I went from high RPM's all the way to idle, it would chug and stall. I raised the idle to 1000 RPM and now it's just peachy.

 

[steve]

Raising the idle speed via the BISS without changing the idle speed in the ECU insures that the ISC isn't working correctly. The only way you can get that higher idle speed is to drive the ISC out of range so that the ECU can't bring it back. Since the ISC no longer works it can't emulate a dashpot or do any of the normal things it does.

Steve

 

[99gst_racer]

Raising the idle speed via the BISS without changing the idle speed in the ECU insures that the ISC isn't working correctly. The only way you can get that higher idle speed is to drive the ISC out of range so that the ECU can't bring it back. Since the ISC no longer works it can't emulate a dashpot or do any of the normal things it does.

Steve

Isn't the main duty of the ISC to control idle speed? So if you manually raise it and have no problems, then are you actually hurting anything by not having a working ISC?? I have a TMO chip and I manually raised my idle to 1000 and I have no problems at all. Everthing seems A-OK..... I was just wondering.

 

[Sean485]

steve is right, if the biss is set for a 750 rpm idle then its fine because the ecu wants a 750 rpm idle, if you try to raise the rpm with the biss the ecu will keep fighting you to keep that 750 rpm idle with the isc until it runs out of adjustment. Whether or not its actually harmful to run the isc out of its adjustment I dont know but there should be no reason to make it idle that high IMO unless you have very agressive cams...

I have a keydiver chip with a 900rpm idle and a fidenza 8lb flywheel. I've never had the car stall once. Even pushing the clutch in off the 8250 rev limiter it dropped to ~800 rpms and then came right back to 900 like its supposed to. I dont belive my chip has anything special as far as compensation for the flywheel as I never told him to add anything and the higher idle speed is just because it will help when i get cams but I think you have other issues other than the ecu. My friends 90 gsx has a fidenza flywheel with stock ecu/idle speed and another has a 95 tsi awd with an act 11lb flywheel and neither have stalled out from letting off at high rpms as far as i know

 

[steve]

There are five pages on Idle Speed Servo Control in the tech manual describing how and what the ISC is used for. Feedback control of the idle speed is a main function but not the only one. It also performs altitude correction, dash pot emulation, and starting assist.
If you have driven it out of range to get a high idle then none of these things work anymore.

If you have a chip then your idle speed could have been changed. If it wasn't you might want to consider getting it changed if you really want a higher idle. Then the ECU will use the ISC normally to maintain that speed instead of working against it. If your chip did have the idle speed changed and you didn't adjust the BISS to match then you would have driven the ISC out of range in the other direction where it can't open any farther when it needs to.

We all know people that have disabled the ISC and FIAV and run ok but the factory stuck this stuff in for a reason and I prefer to keep it working by changing the code if I ned a higher idle.

Steve

 

[Colossus]

I used to have that happen with my fidanza. I ended up with a bad ISC, and it'd just stall out whenever I dropped from high RPM's. I replaced my ISC, and it was just fine.

 

[Sean485]

If you have a chip then your idle speed could have been changed. If it wasn't you might want to consider getting it changed if you really want a higher idle. Then the ECU will use the ISC normally to maintain that speed instead of working against it. If your chip did have the idle speed changed and you didn't adjust the BISS to match then you would have driven the ISC out of range in the other direction where it can't open any farther when it needs to.


Steve

The chip is programmed for the 900 rpm idle and i reset the biss accordingly, what i meant was I dont belive the chip was programmed to compensate for the faster falling of the rpms with a lightened flywheel. I did block off the faiv but the biss is set for the 900 rpm idle and the ecu corrects for the ps at idle and such perfectly.

 

[Ludachris]

The chip is programmed for the 900 rpm idle and i reset the biss accordingly, what i meant was I dont belive the chip was programmed to compensate for the faster falling of the rpms with a lightened flywheel. I did block off the faiv but the biss is set for the 900 rpm idle and the ecu corrects for the ps at idle and such perfectly.

Just so everyone knows my situation - I've adjusted the BISS for the 900rpm setting of the eprom. I've tried running it with the throttle plate slightly open and that didn't help very much - and of course, it created other problems.

I just want to make sure I'm not pulling the tranny for no reason here. If there is a chance that something else could be causing this, I'd like to exhaust a few (easier) options before pulling the tranny.

 

[Ludachris]

Chris,

There may be issues with the ECU dashpot emulation and light flywheels but it also tries to keep the idle speed up when the car is moving. Can you check and make sure your speed sensor is working?

If your using MMCd try logging 0xC6 on the custom sensors page.

Steve

Can I do this with a Pocketlogger? Or do I need to download the MMCd software and install it on my Palm?

 

[Mirage2LTurbo]

Just so everyone knows my situation - I've adjusted the BISS for the 900rpm setting of the eprom. I've tried running it with the throttle plate slightly open and that didn't help very much - and of course, it created other problems.

I just want to make sure I'm not pulling the tranny for no reason here. If there is a chance that something else could be causing this, I'd like to exhaust a few (easier) options before pulling the tranny.

Mine used to do that when I vented my BOV on a stock ecu w/safc. I had to turn up the idle, helped out a lot.

 

[boostcrazy92tsi]

i know this is probably stupid of me but are you running your maft in blow-thru or draw thru? obviosuly if its in draw-thru without recirc its gonna stall out. i have a feeling that the other guys r right and its somethin in the key driver chip thats holding you back.

 

[pneumo]

I adjusted my driving habits to keep my car from stalling after I put in a Fidanza flywheel. I just wait until the engine speed drops to around 1200 rpm before I push in the clutch. Works for me everytime, in any gear.

I'm also hoping the DSM-ECU list will come up with a fix so I don't have to be quite so disciplined all the time.

 

[Ludachris]

i know this is probably stupid of me but are you running your maft in blow-thru or draw thru? obviosuly if its in draw-thru without recirc its gonna stall out. i have a feeling that the other guys r right and its somethin in the key driver chip thats holding you back.

Yes, it is a blow-through setup. I'm not sure what you mean by "something in the keydiver chip is holding me back"... I don't see anyone suggesting that at all. Jeff (at keydiver) has told me that he's never had to program a chip for a lightened flywheel before, which tells me nobody has come across this problem. So what are the chances that I'm the first one to have a blow-through/eprom/flywheel setup and have problems? If anything, the keydiver chip is probably one of the things that can help me if Jeff ever figures out how to adjust the ISC code. I'm just blown away that nobody has come across this problem before me. I'm pulling my hair out here. Can anyone tell me if there's anything else I should check before I change the flywheel (besides TPS and BISS - I've adjusted those several times already with absolutely no success).

 

[Ludachris]

I adjusted my driving habits to keep my car from stalling after I put in a Fidanza flywheel. I just wait until the engine speed drops to around 1200 rpm before I push in the clutch. Works for me everytime, in any gear.

I'm also hoping the DSM-ECU list will come up with a fix so I don't have to be quite so disciplined all the time.

What a pain - after driving the car today, it's clear that I simply have no interest in driving the car this way for very long. Turning into parking lots is almost impossible to keep it from stalling, even if I let it drop down to 1500rpm (which isn't very easy to do). It requires planning for every stop you come to - every red light, every stop sign, every parking lot entrance, every speed bump. If you don't let the car slow itself down in second gear until it gets to about 1200rpm, it will stall. I'm afraid I'm going to get rear-ended by someone who doesn't understand that I have to downshift and slow down WAY before the light. This is simply ridiculous. There must be something I'm overlooking here.

 

[steve]

Can I do this with a Pocketlogger? Or do I need to download the MMCd software and install it on my Palm?

I don't see it listed as one of the parameters pocketlogger can read. The quick way to check is look at pin 11 on the DLC. The speed sensor input to the ECU is brought out on that pin. It will toggle between +5 and ground as the reed switch opens and closes.

Steve

 

[Defiant]

Have you put enough time on it for the ECU to "learn" the engine? It's not your flywheel- the crank and rods have enough mass to keep things alive during a coastdown. I'm suspect it's something in how the flow-through is reading airflow.

I don't want to hear that you've done a flywheel swap only to find that didn't cure it.

 

[1fast97gsx]

my car had this stalling problem with a fidanza flywheel as well. Never had any problems, but once the flywheel went on the rpms would dip really low when reving it or popping it into neutral. With the AC on the car would stall. I ended up adjusting the biss screw which helped a lot, however it still dipped pretty low and almost made the car stall. I never figured it out either .. but honestly the first time I ever noticed it was the day after I installed my flywheel.

 

[Ludachris]

I suspect it's something in how the flow-through is reading airflow.

That's what a friend of mine says. He told me how finicky the GM MAF is and that it very well could be the culprit.

However, I did notice that if I free rev it without pushing the clutch in, it will just stumble without dying. Yet if I rev it with the clutch in, it will die. Does this mean the clutch switch gives input for idle? Why would the ECU care what the position of the clutch pedal is? And why would it affect idle?

 

[MNGSX]

Also if you have an optical CAS swap it for a hall effect.... I had better results with the hall effect one...

The GM mafs are a bit slow..

Profession Flow technologies makes an aftermarket GM signal type MAF that does'nt suffer as bad from these problems... GM Guys use them when the stock one gets lazy.. Cool air and high flow can cause them to read behind. The tricked out ones have been tweeked to handle tweeked engines airflows.

 

[Defiant]

However, I did notice that if I free rev it without pushing the clutch in, it will just stumble without dying. Yet if I rev it with the clutch in, it will die. Does this mean the clutch switch gives input for idle? Why would the ECU care what the position of the clutch pedal is? And why would it affect idle?

Um... the clutch isn't part of the ECU circuit, is it?

However, that is putting pressure on the thrust bearing..... eek.