Why won’t my SUV’s misfire code go away?

John Paul, AAA Northeast's Car Doctor, answers a question from a reader who can't solve an ongoing problem with his SUV.

2018 Chevrolet Tahoe
–General Motors

Q. I have a Chevy SUV with a six-cylinder engine, and it has a misfire on cylinder number five. I replaced the spark plug and recently swapped the fuel injector, but the misfire code still comes up. Could the problem be mechanical or am I missing something? 

A. It is certainly possible that the compression in the number-five cylinder is causing a misfire. A compression test or cylinder leak-down test may help pinpoint the problem. The issue could also be a faulty computer (PCM). The injector is triggered through the PCM. If the wiring is okay then the PCM could be at fault. If you do replace the PCM it will need to be programmed. A close inspection of the spark plug will give you a clue. If it is oil covered, suspect a mechanical problem. If the spark plug is fuel fouled, suspect an ignition or fuel issue. 

John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE certified master technician. E-mail your car question to jpaul@aaanortheast.com.

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