4.0 issue

BigClay

BigClay

Knower of useless ZJ things
Joined
Sep 24, 2008
Location
Winston-Salem
I drove my 98 4.0 TJ yesterday and it was skipping a little and even backfired once when I let off the gas. Also when you rev the motor and let off suddenly it almost dies. Just did new plugs and wires a few months ago, and just had the fuel pump and filter replaced a month or so ago. Two new cats as well.

Any thoughts of the culprit?
 
^
Throttle position sensor? Is that the same thing? keep the receipt because a lot of them are garbage and fail in the first year. I've replaced one that was under the one year warranty.
 
No it's not the same. The crank position sensor is on the top of the transmission bellhousing. It detects signal from the flywheel/flexplate to determine both spark and fuel.

First thing I'd check. Had to replace them in both my 4.0's when they died.
 
Went to crank up the jeep today and it took a long time to start. I let it sit in the garage idling a while then hopped in and reved the engine a little, no backfire, but it almost dies when I took my foot off the gas.
 
Clean the IAC valve. If it's sticky it won't properly follow the engine Rpms under decel as it should. Sometimes causes hard starting as it helps regulate idle speed.

Usually when the crank sensor starts going bad, it runs worse at operating temp and acts normal when cold.
 
What are the symptoms of a TPS going bad?
 
Cleaned the throttle body and the IAC, replaced the TPS and the idle is fixed but it still seems to skip in third gear when accelerating. Going to pull the codes and see if it it the CPS
 
Codes are showing TPS, but I just replaced it so maybe it needs to be reset? Regardless the issue is still there. I guess replacing the CPS is next. Any other thoughts?
 
Reid said:
how much have you driven it since the corrective actions?
Click to expand...

Not much, so maybe it hasn't had time to correct the code, but wouldn't the issue be fixed once the TPS was replaced?
 
Just to wrap up this thread, I finally got the issue fixed. After replacing the TPS and CPS, it ended up being the cam position sensor. Jeep is now running like a sewing machine!
 
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