No start - 91 GP - please help!

[jusber15]

Ok, here is the story. I have a 91 Grand Prix, 123,000 MI. 3.1L. Last week on the way home it kept stalling, but I could get it to start up enough times to get me home. next morning, no start. I have fuel at the fuel rail, spark at all 6 cylinders. I pulled a spark plug and it was dry, no fuel. Seems like the ECM is not telling the injectors to fire...but yet it cant be the crank sensor if it is telling the ignition module to fire (right??) I swapped out the ECM with another and that didnt help. I then changed the Ignition module with another and it fired up and ran perfect......for about 15 miles. it started missing and progressively got worse til it died and wouldnt start again. I got it towed back home and started checking things out a bit and I still have spark, fuel, but the injectors arent firing. PLEASE HELP ME!!! Im going to get fired if I cant get this car fixed in the next couple days. I beg of you.

[jusber15]

No ideas here??? :-(

[richtazz]

When you changed the computer, did you swap in your prom, or leave it like you got it? If you didn't swap the prom, there's your problem, as the same service number ECM can be used for a multitude of vehicles, and the prom is what specifies it to your vehicle.

[jusber15]

yeah, I swapped them when I changed it.

[richtazz]

I would check the wiring harness at the ECM and also from the CKPS for corrosion or broken pins. Fairly common problems, especially on high mileage cars in areas where salt is used on the roads. One more thing, if the GM service number you are replacing is 1227727, you may want to try a reman one, as that part number is more problematic than most, so your chance of getting another bad used one is relatively high.

[jusber15]

I carefully checked the wire connections at the ECM and at many other connections and all looks good. If there was a bad connections at the CKPS, wouldnt that be giving me igniton problems? I have perfect igniton at all times, running or not. What else tells the injectiors to fire? I thank you so much for trying to help me out!!!! :-
D

[jusber15]

:-(

[richtazz]

Did you check your ECM service number, you could still have a bad ECM, especially if it's used.

[jusber15]

I did check it out and I had the bad service number, so I traded it with one out of my other GP that runs and drives perfect, put in my chip and still, nothing. Bought a brand new IGN module...still nothing. Im going insaine!!!!

[richtazz]

have you taken a noid light to see if you're getting a pulse signal at the injectors. A bad fuel pump will cause the injectors to not fire. Fuel pressure at the schrader valve on the rail should be 31-34 psi with the key on/engine off. Starting the car shoud cause a 2-4 psi increase with the vacuum line attached. IF it's under this spec, the injectors will not fire.

[jusber15]

Ok, today I went out and bought a noid light set and plugged it into one of the injectore pigtials. It blinks. It looks like it is blinking faster than my timing light on that same cylinder. Im still trying to find acess to a fuel pressure tester. Any new ideas with this new information??

[jusber15]

Oh wow, I see that you are from Flint. I live just a bit west of Birch Run! :-D

[jusber15]

Ok, now I feel like we may be getting somewhere (I hope). I made up a fuel pressure gauge with some fitting and stuff I had laying around and for what its worth, I have over 36 PSI fuel pressure, key on, engine off. here is what I did next. I disconnected the ECM and turned the key on and with my test light, verified that the pink injector wire is getting voltage. Next I backprobed the green/black wire on the injector and very quickly touched it to ground a few times to "fire" the injector. (when I did this, the noid light on another injector blinked on and off also. Is this right???) I hooked the ECM back up and it started for a few seconds and died. Now since I did that, sometimes when I crank it it will try to run, but just wont take off. A big improvement if you ask me. Is it possible that the ECM isnt putting out enough ground to fire the injectors? When it tries to start, the noid light is much brighter than when it is just cranking without firing. sometimes when I crank it, it dont try to start at all. I did some contituity checks from the green/black injector to the ecm and get a nearly 0 resistance reading. I hope someone can make some sense out of this and possibly point me in the right direction. thanks once again!!