I have a 99xj 4.0, recently started running like crap once in gear. The rpms jump around and if you let it idle in gear it stalls, but not in park or neutral. Replaced tps, map, crank sensot, cam sensor, even ecu. Compression test #1 174 #2 165 #3 135 #4 140 #5 150 #6 155, running out of ideas...

 

Check engine light on?

 

I took to a mechanic near my work, he gave me those compression numbers jefe was saying maybe the gasket or valved of the 3 and 4 cylinders, but I didn't think that was enough pressure loss too cause this. I don't know if it has a cel at this time, when I was testing it showed throttle sensor, cam sensor, crank sensor, 02 sensors, all of which have been replaced

 

Also general rule of thumb is there should be no more than 10% difference in compression between cylinders.

 

If you have access to diagnostic computer you can check for "soft codes". You can also go to a big box auto store and they can check it for you for free.

 

He has a reader, just out to lunch.

 

Compression test specs and procedures for the 4.0 (from FSM).

CYLINDER COMPRESSION PRESSURE TEST

Procedure from 99 FSM but modified by me.

Note that starter duty cycle is 15 seconds on, with 5 minute cool down in between starter use.

The results of a cylinder compression pressure test can be utilized to diagnose several engine malfunctions.
Ensure the battery is completely charged and the engine starter motor is in good operating condition. Otherwise the indicated compression pressures may not be valid for diagnosis purposes.
(1) Clean the spark plug recesses with compressed
air.
(2) Remove the spark plugs.
(3) Secure the throttle in the wide-open position.
(4) Disable the fuel system. (Remove fuel pump relay)
(5) Disconnect the ignition coil (primary connector, not the high tension lead)
(6) Insert a compression pressure gauge and rotate the engine with the engine starter motor for three compression strokes.
(7) Record the compression pressure on the 3rd comression stroke. Continue the test for the remaining cylinders.

Refer to Engine Specifications for the correct
engine compression pressures.

 

I realize this is a hard one to answer but would those compression numbers show a problem that would cause my issues?

 

I don't think so. You may have other problems.

Show the compression check procedures I posted to the person that did your compression check and see if he/she did it that way. If not, have it done again using the FSM procedures.

If you can get any diagnostic trouble codes (DTC) from a scan of your PCM by a code reader or scanner and post them here it would help diagnose your problems. We need the actual codes, not the probable faults. Keep in mind that if somone has read your codes then deleted them, it may take several trips to get them back. DTC's may lurk as pending codes so you need to look for those (CEL not on).

It sounds like replacing all those expensive components was in vain. It could very well be a Transmission Control Model, or wiring, involved.

 

Well some of those were replaced before this problem, but the problem started out with the engine idling fine but in gear and gas applied it would sputter, backfire and barely accelerate, changed tps, map and it got a little better. Now it will rev up and accelerate but still has some sputter and cutting out. Could the injectors be the issue. Ill try to pull some codes after work

 

Test fuel pressure and check for vacuum leak.

 

Has pressure, any idea what vacuum pressure should be

 

Here are the current codes it shows, I also noticed the battery gauge in the dash is not responding.

 

I just meant to check for a vacuum leak. I usually spray carb cleaner around the intake manifold sealing surface and see if there's a change in idle speed.

You mentioned that you replaced the cam pos sensor, but looks like you're still showing a current code for it. Hopefully someone has an idea why.

 

It's not pressure, it's vacuum. You're not looking for a reading here, but for a leak as belvedere suggested and outlined.

No mention of cap, rotor, and wires being replaced. This could be as simple as a breakdown in secondary igniton components under a load.