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Q: Check engine light code for a misfire

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I have a check engine light the code was saying i had a misfire in cylinder 5 i replaced all plugs and wires did an oil change it runs a lot better and quiet but my gas milage is horrible is this normal i have mud tires on my.truck not sure if this is a problem.and i still have a check engine light on like i said it runs a lot better i also put a new air filter in why would my engine light still be on. I replaced everything i needed to for the code

My car has 245000 miles.
My car has an automatic transmission.

A: Hi there. A misfire code is set when the en...

Hi there. A misfire code is set when the engine computer sees a slow down in one or more pistons due to incomplete combustion. This can either be from a lean or rich condition. The task at hand is to accurately determine what is causing the misfire. Check for a crack in the distributor cap or rotor and replace as necessary.

There could also be a leaking injector that is pouring fuel instead of misting. This may account for the horrible gas mileage although the mud tires may contribute.

If I’m not mistaken, this model also has a cold start injector. Verify if the location of the cold start injector is in line with cylinder 5 intake port as a leaking cold start injector would also cause the misfire in conjunction with the gas mileage concern.

I strongly suggest having a qualified technician perform an inspection to prevent replacing unnecessary parts. If you would like to have this done, a certified professional from YourMechanic can come to your car’s location to diagnose the misfire and follow through with repairs.

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