BlksIrocZ

Hello,

Ive had this to many mechanics and nobody can figure this out. Its a 350 TPI MAF car.

On a cold start (outside temperature does not matter, weather does not matter) the car will fire up instantly but immedietely stall. Only way to get it going is to blip throttle up and down over and over until warm then will run fine the whole day unless it sits for more than 4 hours or so. Holding throttle down will stall must be blipped. If i try to for a drive it will stall or hesitate and buck and pop out intake.

I have replaced everything 2 ecms, 3 different mafs even off a working car, new intake and runner gaskets, cts, plugs, wires, cap, rotor, iac (including tos and iac asjustment), new throttle body, new vacc lines, nothing fixes this, and yes good fuel pressure perfect.

The only thing that stops it is unplug maf, fires up runs good, plug maf back in runs great. Shut car right back off (still cold engine) fire up again perfect. Only starting car with an unplugged maf will fire up perfect. Unplugging no other sensor changes the problem.

what the heck is going on please!!!! Its such a pain to start this car every day going on 3 years now

erik69&85

iTrader: (1)

I believe popping out the intake is a lean condition... So it's not getting enough fuel when cold... Is it a ninth injector setup?...

Unplugging the maf sets it a very conservative fuel mix... Usually richer I think... So that is why it probably helps... I think plugging it back it when running doesn't put it in the tuning circuit... I think the ecm still ignores it. I know some maf ecms codes cause the maf to be ignored.... Until you shutdown and refire.... Have had to do this in my car when I was having maf issues....

Maybe this helps... Best of luck.

Komet

Somebody should hook a scan tool / datalogger up to it and see what's happening.

BlksIrocZ

Yes ninth injector is working 100%

Just to clarify i unplug maf start car plug back in, i dont necessarrily have to restart after that im just saying that if i do the problem doesnt repeat. I can just plug in and go but itw very inconvenient and annoying

IROCThe5.7L

Are the injectors stock? Can't hurt to OHM them and make sure they're all in spec.

BlksIrocZ

Injectors have been ohm checked and flow tested hot and cold they are good

tom3

Sounds to me like an air/vacuum leak somewhere after the MAF. Once warmed up and in closed loop the ECM takes care of the extra air. Double check everything again. Might also unplug the vacuum line to the fuel pressure regulator, see if the extra fuel helps the situation.

Vader

If any of those mechanics have blue certificates hanging on their wall, they might as well put a piece of black tape over the "engine performance" endorsement line.

Without data, we're just guessing. A 1988 ECM (1227165) should be capable of data streaming sufficiently to aid diagnosis. There was a mention of fuel pressure being "perfect" but to my knowledge there is no "perfect" pressure for a TPI, thus the reason to vary pressure via the FPR. While possibly being very "inclusive and democratic" adjectives like that are all but useless, whereas numbers have meaning. We might as well assume that the exhaust is "clean" and the idle is "high" - whatever those might mean. The same applies to spark timing, MAF measurements, BLM data from the ECM, other sensor values, and actual EGO measurements.

"Replacing everything" would imply that there is a new camshaft and timing set installed, but there was no mention of that specifically when listing the two ECMs, three MAF sensors, and various gaskets and other sensors.

Unplugging the MAF only proves that the engine will run on backup fuel and spark tables, which we know are intentionally rich and late, respectively.

The cold start injector "working 100%" might imply that it is a massive problem, since it should only work briefly on a coolant temperature and time delay basis, perhaps "5-7%" at most. 100% would be a ridiculously rich condition.

You get extra points for being patient and persistent, however, since dealing with this for three years is beyond the tolerance of a lot of people.

NoEmissions84TA

iTrader: (1)

Along the line of vacuum leak, have you checked the brake booster?
I hole in that diaphragm would be a large vacuum leak.

alan91z28

also have you done a simple check of the temperature sender to the ECM... measure the ohms and compare to known temp when the engine is cold... this can also greatly affect cold engine fueling

BlksIrocZ

I will clarify Fuel Pressure perfect I meant to spec, 43 PSI and holds. Replace everything I meant sensors but I get your point yes not everything. CSI working 100% I meant it sprays fuel while cranking, meaning works as it should. Even if CSI fails it usually just results in longer rank time not start stall condition. I finally got an ALDL and logged data if you care to look, that would be much appreciated.