No compression. Please Help

[Mholbrook]

I recently changed my coils and plugs. Two weeks later I pulled in my driveway and the check engine light is flashing. I took it back to the garage to check it out and the mechanic said there is no compression in cylinder 4. I had a second opinion and that mechanic said he got it to hold compression once but won't hold it again. I'm looking for any input out there from someone that knows the 5.3L flex fuel motor. Thanks

[kevinz]

I would suspect something intermittently holding a valve open. I would have them perform a leakdown test on that cylinder and listen for where the air is escaping. If it's through the intake, then the intake valve is hanging open. If it's out the tail pipe, then it's the exhaust valve.

 

Another possibility, but a very rare one, is that the gaps in the piston rings have managed to line up and leak compression into the crank case. The rings are staggered so they aren't lined up at the factory, but they rotate around the piston in their grooves when the engine runs. Theoretically, the chances are slim to none of the gaps in them lining up, but I have heard of it before. If the air is heard in the crank case during the leakdown test, then it's either aligned gaps or worn rings. To listen for that, pull the oil dipstick and listen/feel for escaping air.

[muddkatt]

Its a very good chance that its a lifter that has failed. If I am not mistaken, #4 is one of the AFM cylinders.