compression test procedure?

K

kshbaja

NAXJA Forum User

Location

OR

• Dec 3, 2005

• #1

i've searched through the archives and found plenty of discussion about the results of compression tests, but not an actual procedure...

when running a compression test on a 97 XJ, is there a need to disable the EFI system? if so, is this via a fuse? which one? any other advice for someone running their first test on an XJ?

 

87manche

NAXJA Forum User

Location

Ohio

• Dec 3, 2005

• #2

The way my dad always used to do it was like this:
Pull all the spark plugs.
Pull the coil wire.
Pull the wires to the ignition coil so the ECU can't try to fire it without a ground for all that high voltage energy.
put the tester to a cylinder.
Tell me to turn it over with the starter.
edit: A quick google search turned up this:
http://www.pumaracing.co.uk/comp.htm
It's a much better explanation and step by step than my words.

 

Last edited: Dec 3, 2005

K

kshbaja

NAXJA Forum User

Location

OR

• Dec 3, 2005

• #3

thanks for the response. the part i was unsure about was how to disable the fuel system on an XJ. i didn't see a fuse for the fuel pump.

 

87manche

NAXJA Forum User

Location

Ohio

• Dec 3, 2005

• #4

could just unplug it at the tank. My 87 MJ has a connector just forward of the tank, and another in the cab behind the seat. I'm sure an Xj would have a plug somewhere.

 

C

cmotsvt

NAXJA Forum User

Location

USA

• Dec 3, 2005

• #5

All I've ever pulled is the coil wire at the coil, not at the dist. you might frizzle yourself if you do that. Youre not likely to have any significant fuel issues although you may be dumping some fuel into the cylinders. Start vehicle when finished to burn any excess off. If your pull all the plug wires at once many people would have a hard time getting them back on right.

 

9

95RedCherokee

NAXJA Forum User

Location

South Carolina

• Dec 4, 2005

• #6

if you arent sure which fuse is for the injectors, just pull the clips off of them.

 

S

summitlt

NAXJA Forum User

Location

Maine

• Dec 4, 2005

• #7

If you dont disable the fuel system youll get better results on the last few cylinders becuase theyre selaing better with the gas.

Disable it.

 

9

95RedCherokee

NAXJA Forum User

Location

South Carolina

• Dec 4, 2005

• #8

If you get unusually low results in one cylinder put a capful of clean oil in the cylinder and do it again. if the results go up, you probably have bad rings.