My truck misfires and will runs rough and only wants to go up to 40mph/usually am/intermittant

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joef answered 3 months ago

Wow, have you considered it to be more than just a misfire on cylinder 4? It could be a fuel delivery problem to the whole engine. Also, are you SURE that you are working on cylinder #4? Check and double check again. What engine does it have? I'll get you the cylinder numbering. Also, can you feel a noticeable misfire while the engine is just idling in park?

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tommcmanis answered 3 months ago

Do a compression test on all cyls this will locate the problem child, a valve w carbon stuck on the valve face will set the light,if you also have back fire it indicates a valve is open upon firing, possible burn valve may be the culprit, this would create a constant runnabilty issue. (Misfire) good compression numbers gas engines 120 - 180 psi diesel 250 - 300 anything below this range will not fire or balance the engine.

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tommcmanis answered 3 months ago

Hope that helps

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tommcmanis answered 3 months ago

Also low fuel pressure can give similar symptoms

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bbourdon answered 3 months ago

joef-The engine is 5.7 liter HEMI. Yes, it misfires while in park. tommcmanis-I have not tried the compression test yet. Thanks

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Curtis answered 3 months ago

How many miles are on it? What maintenance has been done? What happened when this issue started?

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bbourdon answered 3 months ago

87,000 miles. Maintenance-allways oil changes. Truck shaked and did not run faster than 40mph. Now it runs rough/misfires and tends to stop after the engine light goes on. The worst is in the morning. Sometimes during the day.