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I just had some warranty work done on my truck. I had to change the throttle body sensor and the evap sensor. As I was pulling out of the dealer the engine light came on again, turned around and got them to check the code. The mechanic showed me the computer and it said that piston 8 is misfiring. He suggested changing the plugs first and see if that fixes the problem. He also said that if that doesn't work than change the wires, if that doesn't work than the problem is deaper. Do I trust this guy and start with plugs or could it be something else wrong? Also what would be the side effects of letting this go too long?


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contributions: 1992
Images: 37
Location: Oregon
If you had a misfire code for cylinder 8 (P0308) then you probably do have a misfire in cylinder 8. Most scanners also have a misfire counter that you could see all eight cylinders and see if there are also other cylinders that may be misfiring but not enough to set a code yet.

Misfire could be a spark plug. could be an ignition coil. could be spark plug wire. could be an injector. could be something mechanical.

spark plugs would be an easy diagnostic procedure to see if that takes care if the miss. Scoping the ignition pattern and current ramping the coil and injector would give you more information but time wise, replacing the one spark plug and looking at the misfire counter to see if the miss goes away would be cost effective. If it does take care of the miss I would recommend that you replace the rest of the plugs as maintenance. (how many miles are on these plugs in your engine?)

Letting the misfire continue could cause damage to the catalytic converter. (too rich) could burn a valve or damage a piston (too lean, detonation)


   
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I was going to just start with all 8 plugs and see where that gets me. If that doesn't cure the problem than I was going to move on to wires, and than deaper in if I have to. The plugs have 103000km on them so about 60600m. I would say they are due for a change at this point anyway.


   
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I changed the spark plugs, made sure I set the gap to what the truck manual said to. I noticed that it is running a bit smoother but it still seems to be running a little rough. It's almost like it is still misfiring but the engine light has not come back on yet. I did an oil change at the same time hoping that would help. If the light comes back on I am going to change the plug wires. If the light doesn't come back on is there anything else that would make it run rough??


   
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contributions: 1992
Images: 37
Location: Oregon
that's a tough question when I cannot see the engine running. If you have scanned the engine and had a misfire code can you scan the misfire counter and see if there are still some ongoing misfires? Or go into mode 6 to look for misfires below the threshold of setting the check engine light on?


   
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