I have an 04 GMC Envoy 6 cylinder 4.2. The service engine soon light came on this morning and was running a little rough. We ran around a little bit before stopping at Auto Zone, they hooked up there tester and said you have a misfire in cylinder 4. They said it could be spark plugs or maybe a clogged injector. I bought some spark plugs and went home. I shut the car off and restarted a couple of hours later and the service engine light did not come back on and it seemed to run fine. Any ideas?
Could have been some water in your gas if you did not change anything. But most times it's the plugs or plug wires(boots)or coils that cause this code.
If you have over 100,000 miles on it you're due for a tune up. Change the spark plugs and wires (or boots on coil overs). If it's never been tuned up yet you could have a spark plug or wire (boot) that's beginning to fail. HTH. -Jim
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