Braquehunter98

Hello everyone,

So here is the long and short. I have had my jeep for many years. She is a 1993 Jeep Cherokee XJ Country. 4.0 HO with Hesco aluminum head. Engine was rebuilt about 5 years ago. Many add-ons such as borla headers and exhaust, open air intake, throttle body spacer, coil pack and wires.

The poor girl sat for about three years. My oldest son wanted to fix her up to drive to school so we started working on her a bit. A few weeks ago we took her out and romped on the gas a bit. Stripped our brass distributor gear out and she was dead in the water for a few weeks. Got that fixed, now we are having an issue that is driving us to our wits end. She fires right up and runs smoothly. In park/neutral I can run the engine to 3-4k RPMs without any hiccup or any felt/heard issues with the engine. However, once we take the ol' jeep out and she warms up she begins backfiring under load. The backfire and loss of power happens throughout the RPM range, but seems most noticeable at higher RPMs and while accelerating. I believe the backfire is out end and not through the intake as it is felt though the seat of the pants.

We have replaced the CP sensor, Engine Temp sending unit, TBP sensor and coolant temp sensor. The CP sensor seems to have improved idle, but did not get rid of the backfire and sputtering once the engine heats up. We also have replaced the fuel filter.

We need some help. Don't know what is causing the backfire, loss of power, or sputtering... these are the best ways I could describe them. I am out of ideas and do not want to resort to either junking the whole thing out of frustration or spending hundreds/thousands at a repair shop.

Please help if anyone has this experience or knows what would be causing this issue.

:banghead:

Radi

What's the fuel pressure once it warms up? How's the O2 sensor?

Braquehunter98

I will have to test the fuel pressure and I can change out the O2 sensor. The one that is on it is a Bosch, but is a few years old. The issue that seems odd to me is that this is a new issue that seemed to have started right after the distributor gear stripped out. I am not throwing any codes in this OBD1 jeep either (not that it wold necessarily).

ElMartillo

I'd be surpised if it were a fuel pressure problem. A backfire is combustion of fuel/air, though in the wrong place at the wrong time. I'm curious, does it perform the same under the same conditions cold or hot? Idles and revs just fine any engine temp and runs poorly in gear under load whether cold or hot? If it performs fine when cold but not hot, look at the components that effect fuel mixture. Checking the temp sending units was a good move, make sure their wiring and connections on both ends are good.

Personally, I'd be looking first at anything that has to do with your distributor repair and ignition/timing, then Idle Air Control, and the Throttle Position Sensor and maybe 02 sensors after that.