Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
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I suspect this problem is caused by a valve train issue internal to your engine. For example, if one of the valves on cylinder 6 is not opening and closing, it will cause a misfire with a P0306 code and it will still have good compression. To check for this, remove the valve cover and have an assistant crank the engine over while you watch for rocker arm movement on the valves for cylinder #6. If one of the rocker arms is not moving, replace the corresponding lifter. If both rocker arms are not moving, it is possible the solenoid in the Valve Lifter Oil Manifold (VLOM) Assembly may be stuck open.
Excellent! What is the engine vacuum at while the engine is idling?
That is WAY TOO LOW. I suspect that is the problem. You either have a base engine mechanical problem going on or a vacuum leak causing low engine vacuum. It should be close to 19 or even 20 inches of vacuum at idle.
I would recommend to get the intake smoke checked for vacuum leaks and then go after any base engine problems next.
Ok, then we have a base engine mechanical problem that needs to be addressed. I would do a cylinder leak down test on each cylinder and check all rocker arms and replace any as needed.
YES, it could if the valves are not opening. In addition, if the valves are sticking causing an intermittant problem, this wont show up on a compression test because the compression test is done when cranking.. which is less than idle speed.