compression

[ninetysix-ex-jay]

So according to the Haynes manual compression in a 6cyl should be between 120-150. I have a cylinder 1 misfire and since swapped the injector, replaced the plugs, cap, wires, and rotor.

So I did a compression test and cylinder 1 is down to 117psi. The other 5 Are between 128-142.

It's out of range but only by 3psi. That enough to kill combustion in one cylinder?? I threw a can of restore in the oil hoping that would do something.

This isn't my daily driver but what would you guys do here?

[crosbike]

sounds like a tired 4.0. id run it.

[ninetysix-ex-jay]

sounds like a tired 4.0. id run it.

I just really need the check engine light to go out for emissions testing

[Hudson]

You pull all the plugs out and hold the throttle at WOT when you did that test?

120 psi to 150 psi, but maximum variation between cylinders is 30 psi. That's the spec compression for the 4.0. I doubt those 3PSI are going to kill you, but what the hell do i know?

You might get a old style squirt type oil can with the flexible spout and squirt a little oil into all the cylinders and crank the engine for about 30 seconds, then re-do the test. all readings should rise some but a cylinder with a bad valve will rise the least and a blown headgasket not much more than the bad valve.

A good cylinder won't change much either. Bad rings will jump a large amount as the oil will seal them.