Here is what I have checked on my z28 so far...

New Fuel Filter, New FPR, checked fuel rail for fuel pressure, and checked injector pulse... I have no injector pulse... *checked with Ohm Meter*

Here is what the car is doing... Started 1 month ago, Driving down the road, the engine just quit, as if someone turned off the key. Car wouldnt restart.... After tinkering with it for a few days (checking the above mentioned stuff) Here is what I found. The car will start and run for 5 min or so after sitting all night, then the car will just DIE, as if the key was turned off. I checked the pulse at the #2 Injector (easy to get to) and here is what I found... With the car runnning, the injectors fluctuate like it should, rises with rpms, etc. When the car dies, the injectors go dead, and when I try and refire the car, the injectors show nothing... this repeats... If I let the car sit for a day, it will fire again the next, die after 5 min of idle... and the story repeats... I dont know what else to check.

I have swapped the computer AND chip to test, and same thing happens. I have spark, I pulled a plug wire, used a spare plug grounded on the manifold and had a healthy spark durring crank, yet the car wont start... any clue? I dont know where to go from here... Thanks!!!

 

I have come down to the conclusion that it is a sensor causing my problem. When the car is in open loop, it runs fine, but once it goes to closed loop, is when it dies. I need to know what sensors are closed loop reliant. Sensors that would cause the engine to die, but not in open loop. Also, the SES light flashes when the key is turned on, but for some reason, (and even with a 2nd comp and prom) when I jumper the pins on the ALDL port, it wont display any codes... Ideas? thanks!

 

The light should flash once when you turn the key on, that is normal.
As for sensors,
O2 (doubtful it would shut the car off though)
Throttle position (quite likely)
Idle air control (again likely)
Those are the two that wreak the most havoc with the engine when not functioning properly.
Also check that your EGR valve isn't stuck wide open and check the fuseable links down by the starter in line in the wiring to it (look like BIG pills)

 

Someone also suggested that I check the Ignition control Module in the distributer.. said something about it heating up and shutting off (makes sense like when most anything electrical goes bad) and that I must make sure the heatsink is on it properly... does this also sound like it could be?

I have to kinda revoke my theory about closed loop. I have had the car running to 175* tonight... When the car started, I held the RPMs at a constant 2500rpm... it ran just fine, no hickups, studders, stalls, etc... yet... when I let the RPMs drop to Idle... the car died.. and wouldnt restart.. I think whatever the problem is, its either heat related (over heated sensor or electrical component) or its tripping the computer out, but yet on the other hand, if I change computers right after the car wont start, it STILL wont start... so that makes me lean back towards ICM.

*slaps forehead* Man, gotta love mechanical problems! lol.. But where would I be if I didnt have my arms filthy up to the shoulders in grease! Thats an F-Body owners destiny.

Im thinking that the issue could lean either way, I may just swap out the ICM and the IAC just to simplyfy things, cant hurt to have a new one even if it wasnt bad. What would you do if you were in my position?

Also, how difficult is it to change the ICM? I have never changed it, I guess I should have on my last cap and rotor change..

*EDIT* I removed the Throttle Body and removed the IAC housing to inspect the passage and see if it was clogged, but that was fine, I did however notice that the IAC was very black and dirty, so I removed it. I also see that its spring loaded... is the valve supposed to move back ans forth? If so, should I be able to move it by hand? becuase I cant, its frozen. When it is inserted back into the housing, it just about plugs the opening to the passage, is this normal?

 

I think you are naming the same device by 2 different names
ICM= Idle control motor
IAC= Idle air control. Both are the same thing, Just a little stepper motor.

It really sounds like a faulty Throttle position sensor to me, like it may be dead at the lower end somewhere. The IAC is a snap to change, just follow the directions that come with the new one to the letter. The TPS is also easy to change but be careful, the screws that hold it in are alumnium and break/ round out easily. You'll also need a digital VOM to set the new TPS. And if you are going to replace both of those components it'd be a good idea to check/set your minimum air at that time.

 

Im have changed the TPS before and am familiar with how to set it proper with an Ohm meter, however, when I said ICM, I didnt mean Idle Control Motor, I meant Ignition Control Module... I reffer to the Idle Motor as the IAC, Idle Air Control. And that is a 2 min swap. I had had a bad TPS before and it didnt cause the car to die, it just caused it to rev and idle funny... So Im not too convinced that its the cause of my problems, but if my description of the IAC points to it being bad, i probabl will start there, I just need to get to a parts store and compare the two.

 

You can check the TPS very easily with an old analog meter. Disconnect the harness from it and put the meter leads across pins A&B and set the meter to Ohms. Slowly and smoothly open and close the throttle while watching the needle on the meter, it should move in a nice even motion. If it becomes erratic or all of a sudden shows open, you have a bad TPS.

Sorry bout the ICM, some people call it an idle control motor, and in a few manuals too. Nothing like confusing people in manuals.

Doubt it is the ignition module, the HEI modules usually work or they don't, no real in between.

 

Have you checked the injector resistance? If you have an injector that has low resistance, when it heats up it will short out the injector driver in the ECM and cause you to loose injector pulse. When the injector cools down, it will work again until it heats up.
Take your multimeter and check the resistance at very injector(just remove the clip and check across the injector terminals) you should have about 12 ohms resistance. If you see one that is low that is the injector that is causing the problem. If you don't find any that are low, run the engine until it stalls then recheck the injectors. If you do find a bad one, unplug it and your engine should start (but run rough).
Good luck, driveability issues can be tough.

 

I had the same problem and it was the ignition control module. It would run fine if it had been sitting for a while ( like overnight) but after a few minutes it would die and not start up. I replaced the distributor and it's been fine for 2 years now.

Go to Advance Auto parts and get a distributor, put it in, and if it doesn't fix the problem, take it back . Thats what I do. You can call me an a$$, but I know the guys up there and they don't care. As long as youdon't mess it up.

 

I used to think that too, but it's not true.... one part of it does go bad (inj. part) and the rest will work.

 

Yeah, I just may change the whole Distributer, I personally havent changed the distributer itself in the 3 yrs I have had the car... The motor has been rebuilt, but I didnt change it, and the Odometer shows 193,XXX so who knows how old it is. The only thing though is that... IF I hold the RPMS up, I had it running for 20min and it fully heated to 175* and not die, but if I let it idle, it dies, I would think that if it was the Ignition Module... It would kill the motor ESPECIALLY if it was running a higher RPM and especially since its pumping more juice... Sounds like the Idle Control Valve is getting stuck closed or something... But both solutions sound like they will make sense... I will replace the Idle Control Valve based on just what I saw (look really dirty and bad) and If thats not it, couldnt hurt to replace it.

 

I agree with nasty and Jason, I had the same problems, replaced every sensor and went through two ignition modules, last thing I tried before sticking a rag in the tank and torching it was to go to advance and pick up a distributor. 140 bucks later no more problems, it turns out it was the pick up module in the distributor. Dont buy anything else before you stab in a new distributor and ignition module.

 

I definately aggree, I had the exact same problem w/ mine. Pissed me off something awful! I ended replaceing the ECM, wires, plugs, cap, and almost the MAF! Yea, it'll work fine till it gets hot and then just cuts out. Most sensors can be checked at autozone for free and that'll save alot of money when hunting down those problems.

 

the ECM fires the injectors provided it gets reference pulses from the ignition module. if they're not firing, the ICM isn't sending anything. i would go with a new distributor as well.