[CarpenterPope]

Low compression on all 4 cylinders… won’t go over 22,000 RPM

 

[blackedout_taco_stidham]

If anything a completely stopped up cat could cause a spike in compression, but that is a highly unlikely situation all together. You can easily unbolt the cat at the back of the exhaust manifold and just do another compression test.

If all cylinders are low it leads me to think that the head gasket is bad.

Has there been any work done to the truck recently?

 

[reformedwheeler]

Low compression on all 4 cylinders… won’t go over 22,000 RPM

Is that won’t go over 2,200 rpm? Low compression could be bad valves or seats (or some variation of them not sitting right), valve stem seals, piston rings. How low is the compression what are the numbers and are the cylinders dramatically different?


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[CarpenterPope]

All are at 90

today it was running awesome. Had to drive it to move a bunch of tools to a job site

 

[reformedwheeler]

All are at 90

today it was running awesome. Had to drive it to move a bunch of tools to a job site

Do a leak down test.


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[pimpRunner]

What's the mileage on the block?

 

[Twinturborich]

A bad cat can cause low compression, ive seen it a few times, it can't pull in the air or exaust it, if it can't do either compression will be low, remove the upstream 02 sensors then check compression again , if still low add oil to the cylinder and if that raises it the rings are bad, if still low put compressed air on the tester and check where the sir is leaking, if you get bubbles in the coolant its the head. , check with soapy water if you can't fund the leak, out the intake its intake valve out exaust its exaust valve, check those with the valves closed, but if the cats clogged you can look inside o2 hole with a borescoop and find a melted cat or busted up cat, but to answer your question yes a clogged cat will cause low compression and the worse the cat the worse the compression

 

[Twinturborich]

Low compression on all 4 cylinders… won’t go over 22,000 RPM

Yep