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2015 Silverado 1500 5.3 bi-fuel Gas and CNG misfire between 1000-1200 rpm

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  • 2015 Silverado 1500 5.3 bi-fuel Gas and CNG misfire between 1000-1200 rpm

    I have a 2015 Chevy Silverado 1500 5.3 Z-71 Bi-fuel Gas and CNG 65,000 miles. I purchased the truck from Auto nation and they didn't tell me about the issue. When the truck is running on gas there is NO ISSUE PRESENT. When I switch to CNG If I am at a high rate of speed there is no issue, once I hit 1000-1200 rpm accelerating it gently misses. After driving for a few minutes the service engine light comes on switching off the CNG. I can drive the truck on gas for 25 miles or so and the service engine light goes off. I changed the spark plugs and I also checked the CNG filter under the truck on the frame, a small amount of oil came out, the filter looked really good. I took it to auto Nation and they had no idea about anything CNG. Has anybody had this issue?

  • #2
    If the code tells you what cylinder is misfiring try moving the CNG fuel injector between that and another cylinder. If the code moves cylinders that's your problem.

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    • #3
      As Johnm suggests , read the code to find out if it is one cylinder or random misfire. If it's a particular cylinder, easiest first step ,you can swap coils and spark plug wire/boots with another cylinder.

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      • #4
        I had the code read today and it says P219a bank one. The report from autozone says to change the injector. I took all of the injectors on bank one and moved them to bank two to see if the code changed over to bank two but when I drove the truck 100 miles the code is not coming back up and the truck is working on cng with just a super slight miss that almost hard to even detect. Is there a way to narrow down the injector that is causing this slight miss. I could purchase another injector and swap out 1 at a time unless there is an easier method.

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        • #5
          I drove the truck this morning and the service engine light came on. I had the code read again and it has a P219a again so I guess its not the injectors. Could the coil pack cause this? It runs perfect on gas but barely misses on cng causing the engine light to come on thus disabling the cng back to gas. Anybody have any ideas?

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          • #6
            CNG is harder to ignite than gasoline. Any degraded components can cause misfire. Try swapping coilpacks and spark plug wires as a set between 2 cylinders and see if it moves. Unfortunately to get the best codes may require a GM Tech 2 scanner, p219a is supposedly and air fuel ratio , prob not ignition.
            Last edited by Lakewood90712; 09-10-2018, 04:37 PM.

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            • #7
              I had a miss fire with my dedicated factory CNG 2005 2500HD. It turned out to be a fuel injector. I found that the Snap On Solus Ultra scanner I borrowed was worth its weight in gold. It has a misfire mode that shows the misfire counters for all eight cylinders in real time. If you can get your hands on one of these it will tell the story !

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              • #8
                Update:
                The computer is not seeing a misfire. So far I have changed the spark plugs, swapped all injectors, wires, and coil packs from bank 1 to bank 2. I have also inspected all wiring, hoses, vacuum hoses, filter is bright white and clean. I have used 3 different tanks of gas to see if it was bad gas. I was hoping that the code would change to bank 2 so I could start the process of elimination. Again this misfire or stumble only happens when around 1000-1200 rpms about 50% of the time. If I am cruising @ 1100 rpm I can push the gas slightly and stutters just a bit. Other than this little problem the truck runs excellent. Does anybody have any other ideas or maybe has seen this same situation???

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                • #9
                  This is a picture of the SOLUS misfire screen. If you can plug one of these in it will tell you what cylinders are misfiring.

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                  • #10
                    If the truck was misfiring wouldn't it store a misfire code? I have had the codes checked more than 5 times and there was no misfire. Maybe its not a misfire. p219a is a fuel/ air problem I believe. Could this be a bad o2 sensor on bank 1? To bad the Solus is extremely expensive and I don't know any mechanics that would lend me there tool. Also the manufacturer does not have any certified service techs in the Houston area that will work on it so I am stuck trying to figure it out. I was kinda hoping somebody had this same issue.

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                    • #11
                      Misfire can set a" pending code" even if it does not yet set a check engine / service light. Regular code scanners will not see this.Some Ford products need tens of thousands of misfires to set the light. This can happen in a few minutes on a bad misfire.

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                      • #12
                        If you have access to a smoke machine you could trying smoking it when its cold just to check for vacuum leaks. Couldn't hurt.

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                        • #13
                          All vacuum hoses and wiring have been inspected and tested with smoke. No leaks detected. There is a what I assume is a pressure regulator with a vacuum, 2 water hoses, and a drain off hose. There is a hex head bolt head that adjusts clockwise or counter clockwise. I turned it counter clockwise and the stumble or miss would go up in rpms to 1500 as opposed to 1000-1200rpms. I turned it clockwise just to try it to see if it made a difference and it seemed like the stumble was worse at all rpms. Im running out of ideas. Lol. I appreciate y'all's y'all's response thank you. I looked forward to hearing any response or any ideas.

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                          • #14
                            If you turned up the CNG furl rail pressure and the problem moved to a different RPM I would check the CNG fuel rail pressure sensor. Just a guess .

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                            • #15
                              Thank you for helping. Fuel pressure has been checked, cats and 02 sensors checked, all good. Are there any certified CNG tech that is knowledgeable with impco cng systems?

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