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Car dies when coming off throttle??

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car_guy81

Probationary Member
4
0
Jan 30, 2006
Farmington, New_Mexico
I'm helping a buddy tune his GSX. A little background : he bought the car from a board member who just ran out of time, or money, or both and left the car needing a few things after a 1g Cyclone motor swap and manual transmission conversion. The car ran ok, as he did drive it about 12 hours home from LA, but when we got it home we started going through the car and found many things wrong.
Multiple vacuum lines hooked up incorrectly, or not at all. Leaking throttlebody gasket, and a horribly tuned AFC(2000 rpm at -16/3000 rpm at +16WTF ) with stock injectors, afermarket fuel pump(not sure what size), running a Big 16g, and a fmic. Idle was very rough and throttle was not working properly, sticking throttle, and very high idle.

Work done so far: Since we have got the car we have found vacuum diagrams and corrected all vacuum leaks (we think) and the throttlebody gasket leak. Installed new 660cc injectors, checked and corrected timing, BISS, and TPS. We have tuned the AFC on Low Throttle at 30% according to fuel trims with a logger and High Throttle at 80% according to OEM O2 voltage, EGTs, and watching timing advance.

This is what we have done so far, and it is completely possible that we could have missed something with the throttle or vacuum lines.

Current problem: This problem came about when we were tuning for high throttle fuel settings. After a WOT run he would push in the clutch and slow down so we could look at the data and adjust settings. When he would push in the clutch instead of returning to idle the car would just die.:confused: With a small blip of the throttle as it returns to idle it can be kept from dying. Now we have experimented and found that it will even do this at low RPM and lower throttle. In 2nd gear you can put the throttle at 30%, go from 2000-3000 RPMs and then push in the clutch, instead of returning to idle the car will dieWTF . Other than that the car runs great! Everything seems great at WOT and while just cruising around town, you just can not push in the clutch and let it return to idle as you come to a stop without giving it some gas to keep from dying.

Any help would be appreciated. Thanks in advance for the help.;)
 
swarm said:
If the BOV is vented to the atmosphere without a MAF-T, it would cause these conditions.

Thanks. The BOV is still routed back into the intake pipe. :thumb:

One thought we had is that we are not sure of the volume of the fuel pump, and he doesn't have a AFPR of any kind. Could this be causing it to die?:confused:
 
Yes having a larger fuel pump without a decent AFPR could cause a rich condition that would stall the motor. Check fuel pressure to see if this is an issue.

I would be more inclined to think that it is either throttle body related/idle. The high idle/rough idle problem is an issue, and a lot of times when you let the clutch out a TB that is not functioning properly won't 'catch' the engine soon enough so it dies. this includes the BISS, the FIAV and a few other things. I've never had this problem, however I would suggest searching and trying to fix the idling problems first, as I believe that is related to your engine dieing problem.


Or there is this random green wire that is by the P/S pump, that some people have found to negatively affect Idle. do a search for that as well.
 
Thanks, since we have got the car we cleaned out the throttlebody, replaced the gaskets, adjusted the throttle linkage and replaced the fuel injectors. After all that and quite a bit of tuning the AFC, and BISS we have got the car to idle smooth at 750.
I guess we need to round up a gauge to check the fuel pressure. I'll also look into the mysterious green wire. Thanks again:thumb:
 
I just know that the green wire is there such that when you are using the power steering at idle, the car won't die due to the extra load. I'm not sure whether it is better to have this always connected, or always disconnected, or hooked into the proper location.
 
Here's a link to the wire that's being referenced: http://dsmtuners.com/forums/showpost.php?p=151022179&postcount=10 (it's the second pic in this post).

That wire's responsibility, as stated, is to keep the car from stalling at idle when a load is placed on the power steering. I *doubt* this is your problem, but it's always good to be thorough - you want this wire plugged in, so it's best to check it out periodically anyway.

Also, pertaining to your original problems...This is going to sound really dumb, but have you tried resetting your ECU? I slaved over my idle for about a week before getting it to a perfect 750. After all was said and done, I had very similar symptoms to yours (stalling on deceleration being the main problem). Deductive reasoning led me to consider resetting the ECU to clear its retained memory of where the sensors 'used' to be. I unplugged the battery and left it overnight (I'm sure anything more than 10-20 minutes would be fine though), and by morning she was good as new. No more stalling, no more weird idle issues....Doing this will reset all sensors to a sort of "factory default" and allow the ECU to re-learn any new settings you may have applied :thumb: I think my car took about 10 minutes to get back to her "regular self" after I performed this little trick. I haven't had any problems since. I've also had luck doing this on my other car ('03 Mustang GT) -- same outcome.

I just mentioned this as something that might be worth trying -- sometimes it's the simplest things that we overlook :)
 
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