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Ask AMEDEE Your Own Question
Category: Chevy
Satisfied Customers: 26236
Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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I have a 2008 Chevy 1500 5.3. I have a DTC of p0300, with

Customer Question

I have a 2008 Chevy 1500 5.3. I have a DTC of p0300, with number 6 cylinder having most the misfires. pulled number 6 plug and its oil soaked... replaced the plug, and still missed... Pulled the plug again and it was oil soaked again. Pulled all the plugs only one with oil was #6... Put a towel where the plug goes and oil will soak it fast... compression is at 125... I don't know what's causing the oil to get into the cylinder and cause it to miss...
Submitted: 10 months ago.
Category: Chevy
Expert:  AMEDEE replied 10 months ago.

Hello and welcome!

My name isCustomerand I can assist you with your question.

Customer: replied 10 months ago.
Expert:  AMEDEE replied 10 months ago.

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.

Customer: replied 10 months ago.
both are moving
Expert:  AMEDEE replied 10 months ago.

Excellent! What is the engine vacuum at while the engine is idling?

Customer: replied 10 months ago.
16 in at idle
Expert:  AMEDEE replied 10 months ago.

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.

Customer: replied 10 months ago.
smoked the intake... no leaks
Expert:  AMEDEE replied 10 months ago.

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.

Customer: replied 10 months ago.
would it still have good compression
Expert:  AMEDEE replied 10 months ago.

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.