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chevy 2500 bi fuel - round 2

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  • chevy 2500 bi fuel - round 2

    2004 Chevy 2500HD 6.0 bi-fuel. Last summer I had some misfire issues with it that member SIAI47 (http://cngchat.com/forum/member.php?412-siai47) was a huge help with. I had to replace a bad CNG injector that was causing the misfire on CNG. I had all the remaining injectors cleaned and serviced by a shop in california (reccommended on here) and between that and the plug and wires, and cleanout of filters, it ran great all last year.

    This is the first winter with the truck and it is throwing a multiple/random misfire code regularly. It seems to be running fine and has good power, but the computer is obvisously seeing the issue. I thought it was only happening when the engine was cold but it tipped a code yesterday after about 15 minutes of driving. So my question is, since it is a random misfire, and I don't really notice it, where would I start diagnosing this issue? I could throw parts (like changeout coils sequentially) but would prefer to have a more strategic approach to the problem.

    Wish I had access to a Tech2 but that's still out of my budget.
    Last edited by blufie; 02-17-2013, 12:42 PM. Reason: add link to siai47

  • #2
    Re: chevy 2500 bi fuel - round 2

    I am a big time fan of kiss (keep it simple stupid). I would check the plugs and wires first. than if the simple things dont fix it than move on to the more costly ones. it could be a plug that was bad out of the box. or a vac line off or leaking

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    • #3
      Re: chevy 2500 bi fuel - round 2

      What codes are you getting? Are they on all different cylinders? Are they on one bank of the engine and not the other? Do you ever get any codes running on gasoline? Cowboy is right in going for the plugs and wires to the coil packs first if the misfire is random. If you had another CNG injector issue, (or a bad coil pack) the misfire code would show up on a single cylinder. Bottom line is that CNG is harder to ignite then gasoline and ignition problems show up first on CNG---however it could be something entirely different. If you can, you should not run the truck on CNG until you get this resolved as misfires on CNG can quickly melt a caytalic converter and spoil your day.

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      • #4
        Re: chevy 2500 bi fuel - round 2

        Another point to consider is that the ODBII codes can store a first instance at some time much earlier. It may only send the CEL on a second code for the same reason. You would need a code reader to see if codes are stored, prior to the CEL coming on. From my dealings with Bi-Fuel, the CEL is confirmation of a recurring error in a given time frame (like two hits for the same code within so many start/stop cycles).
        '11 Fusion Bi Fuel & FMQ2-36 VRA
        (Former owner '09 Civic GX)

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        • #5
          Re: chevy 2500 bi fuel - round 2

          I will pull the code again tonight and post them but it is always the random/multiple misfire one (P0300 ? maybe)

          I had replaced the plugs and wires and the bad injector 13K miles ago so wasn't expecting to deal with the plug/wire issue again so soon. Last time the engine was misfiring on cylinder 7 more often (but also getting random codes) and it was the #7 injector at issue. You could hear it ticking pretty loud as well. I had the other 7 injectors professionally cleaned at the time. I don't hear any similar sounds from any injectors and the computer has never signaled out any specific cylinder which is why I am shopping for ideas on what to check. I know that there is not much I can really diag without a Tech-2 but thats not an option right now.

          I will move it over to gasoline and see if the trouble follows and then post again. Thanks for the interest!

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          • #6
            Re: chevy 2500 bi fuel - round 2

            Originally posted by raskell View Post
            Another point to consider is that the ODBII codes can store a first instance at some time much earlier. It may only send the CEL on a second code for the same reason. You would need a code reader to see if codes are stored, prior to the CEL coming on. From my dealings with Bi-Fuel, the CEL is confirmation of a recurring error in a given time frame (like two hits for the same code within so many start/stop cycles).
            I have an ODBII module that I use with Torque to read and clear codes. I had cleared all current codes and checked for any "pending" codes between the last occurrence. There were none. It seems to be happening frequently now so i will either find it or it will totally croak (likely taking something else with it lol).

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            • #7
              Re: chevy 2500 bi fuel - round 2

              It was definately the P0300 code. The truck IS definately running rough and I noticed an occasional slight backfire in the exhaust when I held it at 2K RPM for about 30 seconds and the truck RPM's drop slightly when the backfire occurs. I cleaned the MAF (for grins) and checked for obvious vacuum leaks but no change. I was not able to switch the truck over to Gasoline and test but I will this weekend and I will check the plugs and wires too. if the issue goes away on Gasoline then can I rule out a valve issue I guess but not sure what else.

              Should these all be fine then next steps? I am curious about the crakshaft relearn proceedure as a simple maintenance issue that has been seen to help this issue in other forums (tech 2 again - argh!). I also wonder about the EGR valve as these can cause funny idle and erratic performance. I will post again after this weekends work. Thanks for the suggestion and help - feel free to send more ;-)

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              • #8
                Re: chevy 2500 bi fuel - round 2

                You can switch to gasoline by pulling the connector at the tank valve or pulling the fuse that provides power to the lockoff valves to require the truck to run on gasoline. Or (I hate to say it) with the Tech2 you can switch fuels at will If the problem is gone on gasoline then it is most likely a fuel delivery problem (as it is random) which would be easy to find with the Tech2 The crankshaft variation learn procedure is only necessary if you replace the crankshaft position sensor. If you are having problems with it, it should show up on either fuel---and it will throw it's own set of codes. You really need to look at the fuel/air flows and ratios and fuel trims along with O2 sensor performance with the Tech2

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                • #9
                  Re: chevy 2500 bi fuel - round 2

                  Thanks for the info sir, I'm still chuckling . I will keep updates coming on the diagnosis. I really had this thing sorted last year and it ran great for 12K miles. Was hoping for 3 trouble free years.

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                  • #10
                    Re: chevy 2500 bi fuel - round 2

                    Originally posted by siai47 View Post
                    You really need to look at the fuel/air flows and ratios and fuel trims along with O2 sensor performance with the Tech2
                    ''

                    Truck runs fine on Petro. I did double check my coalescent filter, and the metal/rock style filtrate in the mouth of the high pressure reducer. Also checked the aluminum piston (with rubber face) in the lockout at the low pressure side. It was all very clean btw.

                    The Torque program and my odb2 interface has readouts for my fuel trims and pre/post cat lmbdas. What I can't see, is the fuel/air demand and supply. And, I don't know all that I am looking for. The pre cat o2's are fluctuating between .1 and .9 volts -which seems normal. The post cat's seldom read a voltage but occasionaly jump to .8 themselves (on bank one if I remember). This would suggest that the system is running rich at that point but it was not running bad enough to throw any codes (of course) and it has never thrown a rich or lean code. I don't have any basis on what fuel trims should range.

                    Is their anything I can possibly pin down with this level of data, or other claenouts to do? Or any trial and error methods that don't involve $500 worth of parts? I wouldn't mind changing out the O2's but when I hit the injectors they are too pricey to be wrong. I did have all the injectors proffessionally cleaned last year so it would more likely be a failure of one vs dirt anyway.

                    Still at it. I am going to post to som local corvett clubs to see if anyone has a tech 2 they want to rent some time on. Thanks.

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                    • #11
                      Re: chevy 2500 bi fuel - round 2

                      run the van on gas for a long time to completely rule out the ignition system. If the misfire does not come back then you know it's your CNG injectors.

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