Engine will not restart and run?

1991 CHEVROLET SILVERADO
95,000 MILES • 7.4L • V8 • 2WD • AUTOMATIC
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S10ROCKET
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OK, first it started with a what seemed to be bad fuel pump problem. We replaced the fuel pump and it seemed to snowball from there. Now our issue is, when you turn the key forward, you will hear some solenoids click and then the fuel injectors will fire and a little fuel will go into the bowls. Turn the key further and it starts, sounds normal? After running for a while under driving conditions or idle conditions, it will die. When you try and restart it, nothing, just cranks. When you check it again, to hear the clicks, no fuel injectors will fire, but you do here other solenoids click. Now, if I unhook the battery and hook back up, the engine starts right up again and goes through the same song and dance. We have replaced the fuel pump, fuel filter, AIC, TPS, Fuel Pump Relay, rebuilt TBI, and we are going to replace the MAP sensor and the Coolant Temp Sensor, just to make sure we have done them all. We need some help here, Sensors are expensive and we are quickly running out of sensors to change. A little history of the truck, my dad has owned it since 2005 and only put 4500 miles on it pulling a camper a couple times a year so sitting all the time has not been very healthy on the truck. When he bought it, it had all of the high performance ignition stuff on it but over the years it has all gone bad so we have switched it back to stock. I am wondering if it may be the Computer since if I unhook the battery it starts up fine again until it dies?
Oct 4, 2015 at 12:05 PM
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JACOBANDNICKOLAS
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What trouble codes are you getting? When it stalls and won't start, are you getting spark? You mentioned no fuel.

Also, is the ECM a GM component or has someone replaced it to? Since there were aftermarket ignition components, I'm concerned someone may have changed the prom or messed with it. When you turn the key to the on position without cranking the engine over can you hear the fuel pump run in the tank for 5 seconds?

https://www.2carpros.com/articles/car-cranks-but-wont-start

Please run down this guide and report back.
Oct 4, 2015 at 12:51 PM
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S10ROCKET
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I have no way of checking codes here at the house, and Yes it is getting spark when it dies.
I have a buddy that can scan it but he is out of town for the next week. He has one of the cheap scanners from the parts store. I will see if his son can bring it over and I will try and get the codes out of it.
As for the ECM, I have not removed it to take a look at it, what would an aftermarket ECM look like apposed to a oem one?
Oct 4, 2015 at 1:05 PM
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JACOBANDNICKOLAS
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You don't need a scanner to check codes. On the OBD plug, locate port A and B. Place a paperclip between the two and turn the key to the run position (engine off). The codes will be 2 digit numbers. The check engine light will flash, pause, and flash again. Count the numbers of flashes to determine the 2 digit codes. The first one should be a 12.

As far as the ECM, most high performance ones will have their names listed on them. As far as different chips / proms, that is going to be a tough one to identify.
Oct 4, 2015 at 1:20 PM
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JACOBANDNICKOLAS
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AFTER THOUGHT:

You know, if you have spark and fuel, it should run. Try this... when it won't restart, see if it will start a couple seconds using starting fluid. If it does, then we have good spark but no fuel. If that is the case, check to see if you are getting a pulse to the injectors. We may be losing communication between the ECM and the injectors.
Oct 4, 2015 at 1:22 PM
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S10ROCKET
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The OBD plug is under steering wheel correct?

Also, when it dies, the fuel injectors don't fire when the key is turned to the on position. Once you unplug the battery and reconnect they fire.

I will check codes in the morning.

Thanks
Oct 4, 2015 at 1:53 PM
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S10ROCKET
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Well, I just checked the codes and all that flashes is a 12, over and over and over.

Also, the check engine light is not on this morning and it has throttle response. Yesterday just the opposite, throttle hesitation and a check engine light. Tomorrow it may be back to hesitation, this is something else that it is doing, seems like it just depends on how it wants to run each day.
Oct 4, 2015 at 11:04 PM
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S10ROCKET
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As for the ECM, everything appears to be factory.

Did you have any suggestions, have not heard anything since yoru last reply?
Oct 6, 2015 at 5:33 AM
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S10ROCKET
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Also, today I tried to read the codes because the check engine light was back on and I can't even get it to flash 12 now! I am so frustrated I cant see straight...
Oct 6, 2015 at 7:32 AM
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JACOBANDNICKOLAS
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Sorry I haven't gotten back with you. We had a death in the family. Regardless, if it is running good, I have to question sensors... You mentioned that the injectors don't have power when it won't start. Did you check them with the engine cranking? Will the engine start with starting fluid when this happens?
Oct 8, 2015 at 1:01 PM
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S10ROCKET
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Sorry for bothering you in your time of mourning, if you need time I understand.

To answer your question, yes it will start, but just until the fluid is gone though.
Oct 9, 2015 at 6:53 AM
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S10ROCKET
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Also, checked again today and the truck was fine, flashing 12 again. Yesterday and the day before, would not run well, same issues.
Oct 9, 2015 at 12:41 PM
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JACOBANDNICKOLAS
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It almost sounds like the ECM is going bad. That is what signals the injectors to fire. Check to make sure wiring to them is clean, tight, and there is no damage. Check where the harness plugs into the ECM as well for pin issues.
Oct 12, 2015 at 10:08 AM
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S10ROCKET
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Ok, I will check everything. If I have to replace do you suggest new, reman or wrecking yard? also what vehicles will fit the truck?
Oct 12, 2015 at 1:04 PM
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Pulled ECM today, all of the connections and pins look to be fine. Now the problem I am having is, the part number on the ECM does not match anything I can find online. It says 1GM0164953 AWAP, have any idea if that is an aftermarket number and what unit I would use if it is?
Oct 13, 2015 at 9:45 AM
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JACOBANDNICKOLAS
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Sorry for the delay. I was out of town for a family issue. As far as the part number, I would suggest contacting a local parts store to see if they have what you need. If you get one off line, it is hard to tell what you'll receive. As far as part numbers, I don't get them too often anymore, but I had a 93 olds in last week. Similar problem which I diagnosed as the PCM. I got one from the local parts store and it listed three different part numbers which were interchangeable. I removed, switched out the prom, and reinstalled it and the car ran perfectly. Contact them... also, see if someone in your area will test the one you have. I will feel really bad if that isn't the issue and you spend money for the part.
Oct 19, 2015 at 10:27 AM
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S10ROCKET
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I put a new ECM in and it seems to run better, now it will not shift, worked fine before it was towed to my house. Moves in reverse and first gear, nothing after that, GEESH, one thing after another. Any suggestions on that?
Oct 19, 2015 at 12:43 PM
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JACOBANDNICKOLAS
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Is the PCM new? Have you checked to see if there are any new codes? Also, are you sure none of the pins in the connector aren't damaged or pushed in?
Oct 20, 2015 at 10:36 AM
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S10ROCKET
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Well, it's a reman ECM, no pins bent. As for codes, still will not allow me to read them, I put the jumper in A-B and the light will stay on , no flashing at all, only got it to do that one time and it flashed 12. Everything appears to be correct.
Oct 20, 2015 at 12:35 PM
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JACOBANDNICKOLAS
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Did you put your prom into the new PCM?
Oct 22, 2015 at 10:23 AM
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S10ROCKET
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Yes, I put the prom into the PCM.
Oct 22, 2015 at 12:35 PM
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JACOBANDNICKOLAS
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The only thing left that I can even consider is the prom itself. You've checked everything and all was good.
Oct 27, 2015 at 10:41 AM
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S10ROCKET
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Yeah, everything checked out, took it to a shop and after all we had done, found out that the remanufactured computer we just installed was bad. They are replacing it today, they are pretty certain it will fix all the problems. Boy we sure hope so...
Oct 27, 2015 at 10:00 PM
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JACOBANDNICKOLAS
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That is the only thing that was making sense to me. Let me know what happens.
Oct 29, 2015 at 11:03 AM
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S10ROCKET
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Truck is running and shifting as good as ever. However, we do still have one issue that we would like to maybe adjust. How do you adjust the idle speed on a TBI, there are no screws on the throttle like a carb has, so how do you do it. It is idling really high and my dad was wanting to lower it a bit.
Oct 29, 2015 at 10:21 PM
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JACOBANDNICKOLAS
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Glad to hear it's running well for you. As far as the idle, your vehicle has an idle air control valve. The engine idle speed is controlled by the ECM through the Idle Air Control (IAC) valve mounted on the throttle body. Based on different variables, the pintle on the IAC moves in or out allowing air to enter the intake, which in turn controls the idle speed. The IAC is mounted on the side of the throttle body. See pic below. What I suggest is to remove it and make sure it is clean and not sticking and moving freely. Keep in mind, the movement is minimal and that is normal.
Nov 8, 2015 at 8:48 AM
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