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Civic and Chevrolet spark plugs runnin

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  • Civic and Chevrolet spark plugs runnin

    I wanted to share my thoughts while doing some routine maintenance on both my 2012 civic natural gas and my 2015 Chevrolet 2500hd 6.0 bi-fuel.

    Collectively I drive my vehicles 30-40k miles per year, my truck has always had a issue with misfires on startup, that being on cold starts and the switch over from gasoline to CNG it would throw a check engine light. The triggering of the light automatically switches the truck off of cng and back to gasoline, according to Impco this is intentional, Impco and the dealer could never really dial in why it would trigger in the first place.

    To prevent this I have to be driving and have the engine under load. Because at low idle it would always trigger and i would have to plug in a scan tool and clear the code. In reality it's not that big of a deal but while doing maintenance it got me thinking.

    My Civic has just over 150,000 miles aside from the initial startup on my truck I drive exclusively on CNG, I contacted NGK to get the part# for the plugs I needed, the tech I spoke with was very familiar with CNG vehicles, he suggested a new plug that is supposed to perform better for natural gas vehicles. The plug was a Ruthenium HX with a PSPE tip design. https://ngksparkplugs.com/en/product...um-spark-plugs part# LKR8BHX-S (90465), with a preset gap of .032 and a heat range of 8. The gasoline civic has a gap of .044 and a heat range of 7. As it was explained to me with CNG you need to run a tighter gap and 1 heat range cooler.

    This got me thinking about the plug requirements for my truck, which has just over 100,000 miles on it. I then asked the technician for a plug suggestion for this vehicle and he informed me that there wasn't a Ruthenium plug suitable for the 6.0L, but he did suggest a NGK ITR6G9 (90156). This has a gap of .036 and a heat range of 6. The OEM plug that is in my truck is Iridium and has a heat range of 5 and a gap of .044. This plug is more suited for a gasoline engine.

    I am picking up the ITR6G9's tomorrow and I am going to install them, I'll report back what I find out. I'm wondering if my cold start/missfire issue is the result of having the wrong plugs installed.

    As for the Ruthenium plugs I am running on my civic, it seems to have smoothed out the idle and it's running better then ever, fuel mileage picked up a little bit too. This could be because the old spark plugs were tired. Either way these new plugs cost less then 10$ and were much cheaper then the OEM plugs.


  • #2
    I have a 2005 2500hd dedicated CNG. The misfires were driving me crazy until I borrowed a friend SOLUS scan tool. I was able to read the cylinder misfires before the check engine light came on. It turned out the be the CNG injectors. By moving the injectors around I could move the problem misfires. I put a couple of new injectors in and the problem is gone.

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    • #3
      I did the spark plug swap today, most of the old plugs were gapped .044 +/- 2. However 1 of the plugs was gapped at .060, this could of been the cause of the missfire. It seems to be running well after a short test drive.

      The plug change was a huge PITA by the way, especially compared to my Civic.

      John, what is the part number on your injectors, I'm curious to see what's different in injectors with the 10 year spread between our trucks.

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