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'94 Chevy c2500 5.7 Exuast/Engine Timing Problems

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  • '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

    I have a 1994 Chevy c2500 TBI 5.7 v8 that is having major issues. On a cold start everything is fine, but after it hits operating temperature it bogs really low and blows out black smoke. So far we've switched out the ECM, (didnt work) and the Spark Timing Module in the distributor (also didnt work). The previous owner had wrapped the wires going into the timing module with a lot of electrical tape. Also the knock sensor wasn't working until the timing module was replaced. My grandpa (the mechanic) degreed the engine to run in 10 degrees adnvance. Since that didnt fix the problem either, now he is unable to retard the engine back to its original setting for some reason. Only idea that he has left is the PROM in the ECM. CODE 42 SHOWS UP ON SCANNER! PLEASE HELP!!
    Last edited by dcole25; 07-31-2012, 02:44 PM.

  • #2
    Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

    Your coolant temp switch in the intake manifold may be going bad as it controls fuel mixture as it gets warmer. That may explain the black smoke. The timing is controlled by the ecm. But you can set initial timing by disconnecting the single brownish wire behind/under the glove box. That seperates it from the ecm so you can set timing by the distributor. Book says to set it to 0 degrees. I have better luck at 4 degrees btdc.
    HTH
    Last edited by pima.1971; 07-31-2012, 12:50 PM.

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    • #3
      Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

      Def sounds like the Coolant temp switch.

      Basically it tells the ECM what temp the coolant is, and it adjusts the fuel trim accordingly, because a cold engine needs a little more fuel to run right, than a hot engine does.

      When they go bad, they tend to go bad to the cold side, for instance, telling the ECM its -60*F, the ECM responds by dumping in fuel.
      97 K3500 dually Sierra 4X4
      Vortec 454/4L80E
      Crew Cab/Long bed

      95 K3500 Silverado
      Reg cab, long bed
      454TBI/4L80E/BW4401
      4.10's


      95 K2500 Silverado
      Reg Cab/Long bed
      6.5 Turbo Diesel,
      4.10's, 4" straight pipe


      94 K1500 Sierra Z71 OFF ROAD
      Reg Cab, Stepside
      350 TBI
      2" lift, 33's

      Comment


      • #4
        Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

        if your grandpa was messing with timing i would start there.
        O2 GMC RCSB 4.8L V8 AUTO 3.73's
        rebuilt/beefed up 4L60E(at 43,000miles)

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        • #5
          Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

          Ill let him know. atleast it gives him another idea of what to look at. Think the PROM in the ECM would do anything?

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          • #6
            Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

            Originally posted by NEUMANNZZ View Post
            if your grandpa was messing with timing i would start there.

            Hes now able to set the timing. could the PROM be the problem?

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            • #7
              If you replaced the ECM then no, unless you have two bad ecms, as others have said check the coolan temp switch
              1989 c1500- 3' flowmaster, more to come

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              • #8
                Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

                Originally posted by 305guy View Post
                If you replaced the ECM then no, unless you have two bad ecms, as others have said check the coolan temp switch
                The ecm i ordered came without the prom so it has the original prom just a different ecm

                Comment


                • #9
                  Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

                  Originally posted by pima.1971 View Post
                  Your coolant temp switch in the intake manifold may be going bad as it controls fuel mixture as it gets warmer. That may explain the black smoke. The timing is controlled by the ecm. But you can set initial timing by disconnecting the single brownish wire behind/under the glove box. That seperates it from the ecm so you can set timing by the distributor. Book says to set it to 0 degrees. I have better luck at 4 degrees btdc.
                  HTH
                  Checked the coolant temp switch and it was working the other day. checked it again and now it isnt working. no clue why it was working awhile ago and now its not unless we tested it wrong but were switching it with a new one and we'll go from there. Code 42 also shows on the scanner.
                  Last edited by dcole25; 07-31-2012, 08:11 PM.

                  Comment


                  • #10
                    Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

                    42 is from disconnecting the ESC module while setting the timing.
                    97 K3500 dually Sierra 4X4
                    Vortec 454/4L80E
                    Crew Cab/Long bed

                    95 K3500 Silverado
                    Reg cab, long bed
                    454TBI/4L80E/BW4401
                    4.10's


                    95 K2500 Silverado
                    Reg Cab/Long bed
                    6.5 Turbo Diesel,
                    4.10's, 4" straight pipe


                    94 K1500 Sierra Z71 OFF ROAD
                    Reg Cab, Stepside
                    350 TBI
                    2" lift, 33's

                    Comment


                    • #11
                      Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

                      code 42 is timing bypass wire disconnected. disconnect battery to reset ecm and clear code.
                      O2 GMC RCSB 4.8L V8 AUTO 3.73's
                      rebuilt/beefed up 4L60E(at 43,000miles)

                      Comment


                      • #12
                        Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

                        switched the coolant temp switch and it helped a little bit. doesnt run as rich but still isnt running lean enough. gonna put in different spark plugs and see what happens.

                        Comment


                        • #13
                          Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

                          remove and clean ground wire connections at thermostat housing stud. repair grounds if broken or missing.
                          O2 GMC RCSB 4.8L V8 AUTO 3.73's
                          rebuilt/beefed up 4L60E(at 43,000miles)

                          Comment


                          • #14
                            Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

                            Originally posted by NEUMANNZZ View Post
                            remove and clean ground wire connections at thermostat housing stud. repair grounds if broken or missing.
                            Already cleaned the grounds for the thermostat AND the knock sensor. were just guessing on things to replace now. Probably gonna sell the truck for parts and ill have to start looking on craigslist for something to drive :bawl:
                            Last edited by dcole25; 08-02-2012, 10:01 PM.

                            Comment


                            • #15
                              Re: '94 Chevy c2500 5.7 Exuast/Engine Timing Problems

                              Checked for a bad 02 sensor?
                              97 K3500 dually Sierra 4X4
                              Vortec 454/4L80E
                              Crew Cab/Long bed

                              95 K3500 Silverado
                              Reg cab, long bed
                              454TBI/4L80E/BW4401
                              4.10's


                              95 K2500 Silverado
                              Reg Cab/Long bed
                              6.5 Turbo Diesel,
                              4.10's, 4" straight pipe


                              94 K1500 Sierra Z71 OFF ROAD
                              Reg Cab, Stepside
                              350 TBI
                              2" lift, 33's

                              Comment

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