Relative Compression Test

[oldbill]

Is it possible to do a relative compression check on a 2000 Jeep Cherokee with a 4.0L engine. The reason I'm asking is because it has a ignition rail that fires 2 plugs at the same time. How would you be able to only select when number one cylinder fires. One an engine with individual coils per cylinder your could pick the pulse up off of the coil on cylinder number 1.
Thanks,
Bill

 

[RCP Phx]

The only way for that to happen would be if you were running the viper coil with individual wires.

 

[Saudade]

Not sure I follow your question. The engine doesn't run on a compression check. You only crank it with the starter (pull the fuel pump relay). Pull the rail and then remove the spark plug of the cyl you want to check. Might as well do them all. Post the results.

Compression should be 120-150 psi with a 30 psi max variation between cylinders.

Or are you asking about some other test?

 

[Unclewolverine]

I always run compression tests with all the plugs removed, WOT.