Have exactly the same problem as you, except for the oil improving compression, 85 PSI in Cyl 5, between 125-140 cyls 1,2,3,4,6 . Codes 41 and 52 which is TPS and Knock sensor wire, also lean and rich code(cant remember # off the top) Diagnosis is a burnt valve, dead tps, and knock wire is torched and brittle, she has just a tad bit of suction off the tail pipe.
engine rebuilt by POS owner, I mean PO, and she was bored out already. My 3.0 is donezo, not worth rebuilding.
Check you coolant level and oil level, color, smell. Fluid on the floor? also if shes burning coolant it will smell. What do your plugs look like, how does she sound (ping knock tick?) has this gotten worse or changed. how is your power? hesitant? what codes do you have, jumping the daig terminals WILL NOT tell you the complete story. at 42 psi you need to rebuild. if you rebuild, DONT SKIMP on replacement parts, do it completely TOP AND BOTTOM if you can afford too, our bottom end usually is rock solid. Pretty sure my PO did not replace valves or anything
. he did timing, heads and gasket, ended up burning a valve and my gasket is still holding great.
3.0 is notorious for burning valves and throwing head gaskets, there are tons of threads about why/how/prevent this in the future
my .02, answering these questions will steer you toward a diagnosis but I am with Sharpie, a leak down test IS DEFF in order, combined with codes and your compression check you should have close to a definitive answer.
I must judge according to the compression test and oil in the cylinder test.
Linear Mode
