Another rough running TJ

Heath A McDonald

Heath A McDonald

New Member
Joined
Aug 22, 2018
Messages
3
Location
Germantown,Ohio
My first TJ is breaking me in, nicely.

It's hard to start, pretty sure that is the fuel pump (Check valve). What is stumping me:
When it does start, from cold. It sounds like it's running on 4 cylinders (Its a 4.0) Pop the throttle and idle it up and it smooths right out. In high gear (3spd auto) with the converter locked, at approx 35mph with the throttle position just off idle, it acts like it runs out of fuel, loses a lot of power, then will start pulsing like I'm pumping the throttle as I'm going down the road. If I mash it to the floor, it will sputter and then pin you to the seat with acceleration. After that it runs fine until I start driving in the same manner again. If I drive it a little more aggressively, or on the highway, it never stumbles.
I've replaced the TPS, MAP, and, IAC Valve......Any ideas? Is the fuel pump causing this?
Thanks, Heath
 
That sure made me immediately think bad upstream O2 sensor. If you decide to replace it, make sure to ONLY go with an NTK brand sensor. Make darned sure not to use a Bosch. Don't bother replacing the downstream O2 sensor on the cat, it has nothing to do with anything but monitoring the cat's performance.

But it definitely could be a bad fuel pump too. Correct fuel pressure should be very close to 49 psi, you can measure it from the test port on the fuel rail with a rented/borrowed fuel pressure test kit like Autozone loans out. Rev the engine and see if the fuel pressure is keeping up with the engine.
 
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Is there anything on these things Jerry doesn't know? He's an asset to this forum.
 
Just from experience ive seen check wiring harness, mines a 2.5 l and i done all the things that made sence to me to do and moved some wires around at the fire wall and it went to missing just a suggestion think i have a bad wire somewhere lol
 
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