P0300 DTC and Engine Misfire at Idle - Possible Leaking Intake Valves - keywords CEL compression controls excessive high leakage leakdown low MIL miss

This PI was superceded to strictly reference the cylinder head replacement procedure outlined in 07-06-01-018, remove old information that conflicted with the information found in 07-06-01-018, and add an important notice to prevent valve damage. Please discard PIP4013A.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

On rare occasions, a SES light and P0300 DTC may be encountered as a result of single cylinder misfires only at idle. These misfires may or may not be felt and they will disappear off of idle. If the engine misfires do not occur at idle, this PI does not apply.

If the SI diagnostics do not isolate a cause for this concern, perform a cylinder leakage test as outlined in the "Cylinder Leakage Test" procedure in SI and document all leakage rates on the repair order. When performing the cylinder leakage test, it is very important to hold the crankshaft with the related piston at top dead center to ensure that the valves are fully closed or inaccurate results may be obtained. If an aftermarket leakdown tester is used, the instructions of the aftermarket tester should also be referenced because with some aftermarket testers, it may be necessary to limit the air pressure to 50 PSI in order to obtain accurate test results.

If a leaking intake valve is found, replace the cylinder head and valves by following the latest version of 07-06-01-018.

Important: Before replacing the cylinder head, review the latest version of PIP3940, which contains some tips for using the lower timing gear tensioner holding tool (EN48464) described in the latest version of 07-06-01-018. This bulletin contains a revised cylinder head replacement procedure that no longer requires removal of the oil pan, front cover, water pump, or crankshaft dampener. Also, as mentioned in 07-06-01-018, it is important to install the cylinder head before you install the camshafts. Once the head is installed, the J44221 (Camshaft Holding Tool) should be used to hold the cam flats as the camshafts are installed with the #1 piston at top dead center. If the cylinder head is installed with the camshafts in place, without using the J44221 to hold the cam flats, or without the #1 piston at TDC, one of the valves could bend, resulting in an engine misfire at idle once the repairs are complete. As a result, it may appear that the new head has the same concern as the cylinder head that you just replaced, when it is actually the result of a bent valve.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.