Ok, I have seen you had some bad luck on isolating this problem. Let me say, you have trusted us with your concern with no luck. Lets try to resove your issue, before you accept my answer's. We rather you be happy with our help. Ok, I am thinking maybe a valve is not seating properly, causing this problem. here is the instructions, let me know what readings you come up with.
Cylinder Leakage Test
J 35667-A Cylinder Head Leakdown Tester or equivalent
A leakage test may be performed in order to measure cylinder/combustion chamber leakage. High cylinder leakage may indicate 1 or more of the following conditions:
| • ||Worn or scored cylinder bore|
| • ||Cracked or damaged cylinder head|
| • ||Cracked or damaged engine block|
Disconnect the battery ground negative cable.
Remove the spark plugs.
Rotate the crankshaft to place the piston in the cylinder being tested at top dead center (TDC) of the compression stroke.
Install the J 35667-A or equivalent.
It may be necessary to hold the crankshaft balancer bolt to prevent the crankshaft from rotating.
Apply shop air pressure to the J 35667-A and adjust according to the manufacturers instructions.
Record the cylinder leakage value. Cylinder leakage that exceeds 25 percent is considered excessive and may require component service. In excessive leakage situations, inspect for the following conditions:
|• ||Air leakage noise at the throttle body or air inlet hose that may indicate a worn or burnt intake valve or a broken valve spring.|
|• ||Air leakage noise at the exhaust system tailpipe that may indicate a worn or burnt exhaust valve or a broken valve spring.|
|• ||Air leakage noise from the crankcase, oil level indicator tube, or oil fill tube that may indicate worn piston rings, a damaged piston, a worn or scored cylinder bore, a damaged engine block, or a damaged cylinder head.|
|• ||Air bubbles in the cooling system may indicate a damaged cylinder head or a damaged cylinder head gasket.|
Perform the leakage test on the remaining cylinders and record the values.