Grand Prix no start mystery

[Sunspot]

50psi fuel pressure
TPS reads right on
Have not tried another ICM, but I have good blue spark at tops of each coil post

What about my reading that says current gear is 3....what does this mean?
If I had another car sitting there I could compare readings, but I don't

What should the crank sensor read key on engine off?

[HotZ28]

Once again, are all the injectors firing? Do you have a noid light set?

[Sunspot]

I will check injectors this morning

[Sunspot]

Here is a new part to this mystery
This morning after sitting in the shop overnight, the car started
I had to give it alot of pedal to keep it going and it burned really black smoke for about 45 seconds and then slowly cleared out
Wouldn't idle until I unplugged the MAF
I sprayed carb spray all over while it was running and no change
I watched reading while it was running and most of the odd ones became normal
Air Fuel Ratio was now 14.7:1
Current gear 1

Long tewrm fuel trim running -28 to -39
Short term FT running was -14 to 3.9
all FT reading fluctuated

So who wants to bet on a vacum leak that mostly seals itself up when the metals on the motor expand?
What vacum leak would the carb spray not reach? lower intakes internally?

[tblake]

Originally Posted by Sunspot

So who wants to bet on a vacum leak that mostly seals itself up when the metals on the motor expand?
What vacum leak would the carb spray not reach? lower intakes internally?

Sounds like a good assumption. I thought from the beginning you might be doing LIM gaskets again on this one after you mentioned the leaky t-body gasket.

Still that doesn't explain why your sensor readings were all askew.

And the car only idles with the MAF unplugged? You may still be looking at a bad MAF sensor. Is there any way a MAF can fail and cause other sensor issues? Like does it share the same ground with a Crank Position Sensor?

[Mickey#1]

A vacuum leak should make the fuel trims go positive not negative.

[Sunspot]

If the vacum leak gap has closed because of the temperature shift, I guess the carb spray wouldn't work. But, you would think there would have to be at least a little leak still if that is the case. Right?
I had sprayed the carb spray outside too while it wouldn't start, and that didn't change anything either, if the gap was huge out there, why didn't it suck the carb spray?

Where would an internal vacum leak be?

Could there be anything else that is so temp. sensative besides vacum gaps?

[tblake]

Internal vacuum leak would be to inside of the crankcase. On the vehicles with external PCV valves like the 3100, to test for internal vacuum leaks, you would remove the pcv valve from the valve cover leaving it attacted to the vacuum source, plug the pcv valve with your finger, then spray carb cleaner into the valve cover and listen to see if the idle stabilizes, or in your case if it starts. To test for internal vacuum leaks on the 3800sc motor, I have not a clue.

[Sunspot]

While idling, I plugged the MAF sensor back in and it quits instantly and would not restart
Unplugged it again and zooms right off
But, remember that the last couple days when it would not start, I also had the MAF unplugged.
Makes no sense

[Mickey#1]

Sounds like it's time for a new MAF sensor. What's the scanner showing for the MAF? Can you get a reading at idle & again at 2,000 rpm?

[Mickey#1]

I guess it would be hard to get a reading when it dies while plugged in. Get a MAF sensor, they're expensive you might want to get one from a junkyard since were not 100% sure what's going on with this car.

[3100]

this is not vacuum leak - as Mickey said vacuum leak would cause ltft to go positive and iac count would decrease and be closer to 0. What is your IAC reading.

Now since you have engine running drive it around with scanner and try to record some freeze frames, and also give us some more live engine data.

Black smoke means reach mixture, and even ltft is telling you that so it is obviously giving too much fuel or it is not getting enough air.

disconnect af O2 see if it will run better..
- valid GM maf test, = while engine is running hit the top of the maf sensor with the handle of the screw driver if engine rpm changes replace maf.

[Sunspot]

I am pretty sure that unplugging the MAF puts the car in limp mode, which would alow it to run. Might not necesarily be a MAF that is bad. I wish I had a know to be good part laying around!

[Mickey#1]

I would think a garage would have a real good relationship with the local parts supplier. Won't they let you return one if it doesn't fix the problem?

[tblake]

And if they wont, you will have a good one on the shelf to use for future diagnosis!