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1991 Silverado 350 TBI Cuts Out Under Acceleration

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  • 1991 Silverado 350 TBI Cuts Out Under Acceleration

    Hello everyone, I'm sorry this is long. I am have been having some trouble with my truck. As the title states it's a 1991 Silverado 350 TBI. The problem is under moderate to hard acceleration, the engine engine will hesitate or hold back to completely cutting out depending on how much the throttle is pressed. If pressed 3/4 or more the engine will cut out just like it shut off, then it will buck a few times, then pick up and rev up like normal. This only happens when the engine temp is between the 40-90 degree mark on the temp gauge. Once the truck reaches operating temp, it runs fine. I can take off with the throttle to the floor and it goes like it should. Also I should note, black smoke comes out the tail pipes after the bucking clears up.

    The fuel pump was replaced because it actually did fail, at the same time I replaced the fuel filter, the TPS has been changed and while performing my second block, I scoped the reference and all was fine. I replaced the temp sensor, O2 sensor, I checked out the EGR, all to no change. I unhooked the MAP sensor and nothing changed there, I just didn't try testing it out with a another. I checked the fuel pressure regulator spring, all was good. Timing is dead on, myself and anyone I've talked to and demonstrated this to is at a lost. I've checked the distributor and there's no play in it, gave it new cap, rotors, wires and plugs.

    Like I mentioned, this only occurs when the engine is between the 40-90 (just before the 100 mark), and it's every time. If I accelerate lightly, you can feel the engine loose power for a few seconds, then feel it come back. I would describe it a little worst then if you were driving a 4 cylinder and the A/C compressor engages. No DTC's present. Thanks.
    Last edited by mullint; 03-21-2012, 01:45 PM.

  • #2
    Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

    Did you change the temp sensor on the block or on the intake? If I remeber right the intake is just for the gauge and the one on the side of block is for the ecm. Also check all grounds. You really shouldnt drive it that hard when its that cold though. It causes a lot of engine wear.
    94 ECSS 4x4 All stock, Come get some son
    99 blazer 4x4
    86 Coupe DeVille

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    • #3
      Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

      I normally don't drive hard. I come across this a couple years ago accidently when someone was allowing me to turn. When I pressed the throttle down half way to make a quick turn, the truck just sat there and bucked. You could basically hear each cylinder firing. The problem is present under normal driving, just not to the severity that I described. It's like it's holding back momentarily under normal acceleration.

      As for the coolant sensor, I replaced the one in the intake. That one appears to be for the ECM, as when I did unplug it, the engine ran horribly and extremely rich.
      Last edited by mullint; 03-21-2012, 02:02 PM.

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      • #4
        Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

        Yes your right the one on the intake is for the ecm. I would check all your grounds next.
        94 ECSS 4x4 All stock, Come get some son
        99 blazer 4x4
        86 Coupe DeVille

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        • #5
          Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

          What grounds should I look at. I've thus far for grounds ran a 4 gauge wire from the engine block direct to where the battery grounds on the body. I cleaned the grounds in the junction section on the firewall. Could you please direct me to where other grounds should be checked? thanks
          Last edited by mullint; 03-21-2012, 02:24 PM.

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          • #6
            Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

            That's all good stuff. Check/clean the one by the thermostat. That's the one for the ecm.
            94 ECSS 4x4 All stock, Come get some son
            99 blazer 4x4
            86 Coupe DeVille

            Comment


            • #7
              Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

              knock sensor hooked up?
              timing advances when revved up?
              when cold is idle high then settles when it warms up?
              O2 GMC RCSB 4.8L V8 AUTO 3.73's
              rebuilt/beefed up 4L60E(at 43,000miles)

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              • #8
                Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

                Knock sensor is hooked up, I did unhook it while trying different things out. Timing does advance when reved, mind you the engine was up to temp when I checked. Idle at cold is fast and does settle down as it warms up.

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                • #9
                  Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

                  can you post results of a diagnostic scan or datalog when cold and fully warm?
                  O2 GMC RCSB 4.8L V8 AUTO 3.73's
                  rebuilt/beefed up 4L60E(at 43,000miles)

                  Comment


                  • #10
                    Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

                    Ok, I checked and moved the ground for the PCM from where it was to a good clean ground with no difference. As far as the scan, all I can tell you is that I get code "12", which is everything is ok.

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                    • #11
                      Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

                      what do you mean by performing my second block, I scoped the reference ?

                      post results.
                      Last edited by NEUMANNZZ; 03-22-2012, 11:40 AM.
                      O2 GMC RCSB 4.8L V8 AUTO 3.73's
                      rebuilt/beefed up 4L60E(at 43,000miles)

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                      • #12
                        Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

                        I was doing my second block for my mechanics license, which I gave up on after getting laid off numerous times. While I was in the college I used a scope machine to check for any bad spots on the TPS 5V reference signal.

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                        • #13
                          Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

                          check fuel pressure.
                          ensure egr valve is working properly:
                          http://www.fullsizechevy.com/forum/g...eshooting.html

                          check for clogged cat.
                          O2 GMC RCSB 4.8L V8 AUTO 3.73's
                          rebuilt/beefed up 4L60E(at 43,000miles)

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                          • #14
                            Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

                            Thanks I'm going to look into that over the weekend hopefully. Very informative.

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                            • #15
                              Re: 1991 Silverado 350 TBI Cuts Out Under Acceleration

                              My Brother is having a very simular problem and we are having trouble hunting down the problem. I'll keep track to see if you can find out what the problem is.

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