awolfalone2006

Ok, I'm working on an '87 Vette. I know this is a Camaro forum but I'm not going to join a forum for a car I don't own. Anyway, the car is starting and stalling shortly after. Sometimes it will keep running smoothly, but not always. Sometimes it stumbles then keeps going. Once it gets past that stumble, no problem. Fuel pressure is 44psi with large dips, I tried bypassing the oil switch for the fuel pump but no help there. All injectors measure 16 ohms. With a noid light the injectors pulse the whole time it is stumbling or dying, just not as bright as when running. MAF shows 3gm/s when dying, 10gm/s when idling. Someone previously installed a duracrap MAF and fuel filter. EGR valve wasn't fully seating so that is new. No vacuum leaks I can find. ECT on the datalist always matches the gauge and infrared thermometer. Cleaned the throttle body, replaced the IAC when it broke as I was cleaning it. Has spark the whole time it is dying. I have found that if I add propane as an alternate fuel when it is dying out that I can keep it running that way while the injector pulse on the noid light is weak. No codes. Clear air filter. New spark plugs. Doesn't matter what temperature the engine or intake air temps are.

Fuel, air, spark, compression. Should be simple but has been kicking me all week. My training and experience has all been on newer, mostly OBD2 vehicles and this is the first TPI I have messed with.

Looking for something to try.

I won't be online all weekend so if you ask me questions I won't be able to answer until Sunday night at the soonest.

greenyone

iTrader: (1)

There is a procedure for setting the TPS and IAC. I assume you did that when you replaced the IAC?

awolfalone2006

I was just coming back to say I did that. I forgot to put it in my first post.

alan91z28

since you have a scanner i assume as you are reporting MAF numbers, what do you see the IAC counts as, ie what is it doing during this time

also what are you seeing for fueling?

have you also checked that initial spark advance is correct, ie 6 deg with ECM adjustment unplugged?

on the fuel pressure it will move around with the vacuum line attached to the regulator is that what you are seeing, ie what is the condition you are measuring the fuel pressure. also if you shut the key off does the fuel pressure hold or collapse quickly

couple easy things to check

awolfalone2006

I will check the IAC count.

Fueling as in a parameter in the datalist?

Fuel pressure was bouncing with the vacuum line hooked up. I wasn't really worried about that small variance, even less worried about it now that after an injector clean (this thing only has 70k on it) the needle is dead steady. There is no bleed off of the fuel pressure.

I have a hotline tip to check the cold start injector, even though this isn't dependent on temperature. Going to look into that too.

Bob88GTA

iTrader: (2)

Just a something to check.
Your Cold Start Injector IS dependent on temperture. It's location is by the Cold Start Injector Switch on the front of the intake. If intake temp is above a certain degree, it does not activate the CSI. If your having this problem even after a warm restat, the CSI does not come into play.
Usually just what it says.....COLD START INJ. I beleive that temp is around 120*.

battman

iTrader: (2)

Going from the information in your first post about the dimming noid light, sounds like you might have a grounding issue with the engine and ECM or there is a problem with the injector driver circuit in the ECM.

A good place to start would be to check the ECM grounds on the back of the heads.

awolfalone2006

Thank you for the responses so far. Update:

Starting better and more consistently since the injector clean. I may be dealing with a serious case of lot rot and chasing ghosts. Still stalls out or stumbles on start occasionally though.

I realize the cold start cuts out, I had to ground out the thermal time switch connector to test the injector, good pulse on the noid light and fuel pressure drops when cranking and all other injectors unplugged. It is working properly. I'm just willing to check it in case.

IAC counts: 144 before cranking->89 stall. 144 before cranking->89 start->75 at warm idle.

~5.5* base timing. I have an adjustable timing light so I can dial in the flash on zero. 5 and 6 put it on either side of TDC.