Cylinder 6 Misfire Code

[manwiththeplan88]

I have a 1997 4.3l V6 blazer and my check engine light came on and turned out that is was a code for cylinder 6 misfire. The plug wire for that cylinder tested good and looked fine(only 4 months old). When I pulled out the spark plug it seemed a little burned so I replaced it with a new AC DELCO spark plug. I have two main questions:
1) If the spark plug was the problem, now that I have replaced it will the check engine light eventually go off on its own or do I have to clear it then let it reboot?

2) What are the main causes of this problem (cylinder 6 misfire and/or burnt spark plug) and what can I do to fix it?

[old_master]

If the problem was the spark plug, the SES light will turn off by itself, or you can have all of the DTC's cleared with a scan tool. Disconnecting the battery will not clear the history file codes in the ECM.

There are several causes for DTC P0306: Vacuum leak, spark plug, spark plug wire, distributor cap, fuel injector stuck closed, fuel injector stuck open, leaking fuel injector O ring, open circuit in fuel injector, open circuit from ECM to injector, bad injector driver in ECM, burnt intake valve, burnt exhaust valve, worn lobe on camshaft, collapsed lifter, bent push rod, just to name a few.

[manwiththeplan88]

Thanks for your input old master, I took my vehicle to my mechanic and all they say is that it will take a lot of time and/or labor (which I cannot afford) to pinpoint the problem since it could be so many things as you mentioned. I also just found out my coolant resorvoir was emtpy! Do you think this could be a cause for the misfire and/or burnt spark plug? Also a guy at autozone recommended I use lucas fuel cleaner in my vehicle. Any thoughts?

[old_master]

The low coolant level could definitely be a clue! On your engine, there is a coolant passage in the rear of each cylinder head. The passage does not go through the intake manifold. The passages are sealed off by the lower intake manifold gasket. #5 and #6 intake runners are very close to the sealed off passages. The lower intake manifold gaskets are known to fail pretty regularly due to the inferior design. It's very possible for coolant to leak into the #5 and/or #6 cylinders if the gasket fails close to a runner. A cooling system pressure test may not reveal an external coolant leak, but may show a loss of pressure.... that would be coolant leaking internally. Coolant can leak into the runners or into the crankcase, or externally, or any combination of the 3. Felpro makes a greatly improved gasket set, (MS98002T) that will not leak if installed correctly. You might find that Autozone rents a cooling system pressure tester. If they do, perform the test when the engine is cold, and again when it's hot. Leaks can be tricky to find, and if you can't find any external leaks, chances are real good it's the lower intake manifold gasket. Keep us posted.