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1991 GMC K1500 5.7liter Stalling issues

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  • 1991 GMC K1500 5.7liter Stalling issues

    To all of the GMC experts out there, I need to pick your brains:

    I have tried to search the forum for answers but was unable to find an answer to the kind of problem I'm having. So here's what I got:

    I have a 1991 GMC K1500 5.7 liter tbi.
    Problem:
    Truck starts up fine and will run for a few moments and ubruptly stall out at idle. It also stalls out when approching a stop. It seems as though it starves for gas. It will usually start right up but now its taking longer for it to start back up after stalling. It also has a slight miss. It does not stall out as long as I give it gas. When approching a stop, I usually have to pop it in neutral and give it gas to prevent stalling. However, I notice that the stalling becomes less frequent after the truck has been driven for about 20 minutes, give and take. It does not stall out all the time nor doesn't stall while I'm driving.

    Checked and replaced:
    I have replaced plugs and wires, Distributer cap and rotor, pvc valve, battery, alternator, oil and oil filter, fuel filter, fuel pump, fuel fump relay.
    I have checked the EGR and the IAC valve, I have 9psi fuel pressure, I have spark, the "engine service" light does not come on. I have taken the truck to a mechanic so he can run a diagnostic check and he found nothing wrong. He said the fuel injectors may be causing the slight miss and to add fuel injector cleaner to the tank. He said maybe the new fuel pump I installed could possibly not be working properly.

    I am not too experienced when it comes to working on trucks but this truck may be slowly turning me into an expert. I have read other postings on here and what they did to fix their problems, like changing the ignition module or the coolant temp sensor. However, i'm not as knowledgeable as many of you are and so I come to you if anybody has any possible idea what is wrong and what I can do.

    Thanks,
    Joe

  • #2
    Re: 1991 GMC K1500 5.7liter Stalling issues

    I guarentee its your ignition module. Whenever I see threads like this, I always say its the igniton module, people change them, and its fixed. My truck was having the same problem. I replaced everything like you did and I still had the problem. Replaced the ignition module. Fixed. :read:

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    • #3
      Re: 1991 GMC K1500 5.7liter Stalling issues

      It could also be the IAC motor. This is what controls idle on all EFI engines. With age these tend to get alot of carbon build up around the plunger and air passage area, which will interfere with it's funtion. They also go bad with age, and not always will it set a code. You can remove it and use some carb cleaner to clean the plunger and air passage port opening. If your problem is the IAC motor, and if carbon build up is the issue, cleaning will solve your problem. I've had brand new ones that are defective.
      Last edited by 8388; 08-21-2007, 05:57 PM.

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      • #4
        Re: 1991 GMC K1500 5.7liter Stalling issues

        Originally posted by 8388
        It could also be the IAC motor. This is what controls idle on all EFI engines. With age these tend to get alot of carbon build up around the plunger and air passage area, which will interfere with it's funtion. They also go bad with age, and not always will it set a code. You can remove it and use some carb cleaner to clean the plunger and air passage port opening. If your problem is the IAC motor, and if carbon build up is the issue, cleaning will solve your problem. I've had brand new ones that are defective.
        I was thinking it is the IAC also.
        1991 C1500 Ext. Scrapped. I still have the engine, tranny and Detroit tru-trac.
        2005 GTO LS2 with full Pedders track II suspension. StreetsweeperHT cam with Kooks exhaust. Tuned.

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        • #5
          Re: 1991 GMC K1500 5.7liter Stalling issues

          i might be totally wrong here, but my truck did the same thing and it was my cam, i took a lobe off it and screwed a lifter.
          2001 GMC 1500 RCLB 4x4 5.3 Cherry bomb Extreme, Timberline M/T's
          1989 Chevy 1500 RCLB 355 little bit done, but to people i see on the street its stock

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          • #6
            Re: 1991 GMC K1500 5.7liter Stalling issues

            The easiest way to really be sure what the problem is is to find someone with a scan tool which will let you view engine data... Hard to diagnose over the internet. Sorry.
            4th year GM Apprentice - on active Army service.

            1990 GMC Sierra C1500.
            350 w/comp cam, superchips computer, K&N air filter, dual Magnaflow exhaust, 3.73rear end, brown and bronze paint (with stylish orange pin-stripe), and rust.:puke:

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            • #7
              Re: 1991 GMC K1500 5.7liter Stalling issues

              Originally posted by Alexander
              The easiest way to really be sure what the problem is is to find someone with a scan tool which will let you view engine data... Hard to diagnose over the internet. Sorry.
              If you read, he already put a scan tool on it, and it turned up no codes :read:

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              • #8
                Re: 1991 GMC K1500 5.7liter Stalling issues

                There is another tool that can be used to diagnose the problem, but it does require that you know what the voltage values are for each of the sensors that will be tested. All sensors send signals to the ecm. These signals are in the form of millivolts. One can use a volt meter that has the capacity to read in millivolts, to verify that the sensors are operating within the values they are set to work within. This is how I determine if the sensor or it's wire is the culprit.
                Last edited by 8388; 08-21-2007, 11:34 PM.

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                • #9
                  Re: 1991 GMC K1500 5.7liter Stalling issues

                  Thanks guys for all of the information. I'm not exactly sure what all was involved as the mechanic diagnosed the truck, but it cost me a little over $50 and he found NOTHING!!...ugh.
                  Advance Auto parts said they can check the Ignition control module for free if I bring it up there. They also recommended that I should look into replacing the Ignition Pick-up and Ignition coil which could possibly solve my problem. I will go first with getting the module checked first.

                  [U]Question:[U]
                  Please excuse my ignorance, but when you say "IAC motor" are you referring to the "IAC valve"? I have a Haynes manual and it only mentions "IAC valve". Again, thank you ALL for the advice. It is more than appreciated!

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                  • #10
                    Re: 1991 GMC K1500 5.7liter Stalling issues

                    I had the same problem and what happened was my idle would drop to 300 rpm and what happened was two of my idle control wires got cut and it caused it to do that. So check by your firewall and under your glovebox.

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                    • #11
                      Re: 1991 GMC K1500 5.7liter Stalling issues

                      Alright guys. I took out the ignition control module and brought it to the parts store to have them check it for free. They said there was nothing wrong with it BUT, their equipment isn't 100% accurate. SO, I went ahead and bought a new ignition control module and put it on. So far it hasn't stalled out, yet. I drove it around quite a bit yesterday and its running much better. It has taken me 4 months trying to figure out what the hell was wrong with my truck. But thanks to all of you guys, Its finally back on the road again. Thank you all again.

                      Joe
                      Last edited by jafacct6778; 08-26-2007, 07:39 AM.

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