Question On A Major Hesitation

I am a new member to the xj scene, I can now do all the tight technical trails that my fullsize heeps never could fit. I purchased a '90 xj with 55k miles on the stock 4L, did normal maintenance and wheeled it for a few months. What a great truck, ran like a top! The problem that I now have is a major drop off in power at certain rpm's. (especially when not very hard on the gas) It feels like the motor is running out of fuel. I can make the engine stay in this situation for a few seconds and it will start to thud (knock). This has put both me and my girlfreind in some hairy road situations. I have replaced the fuel pump, pressure regulator, all normal tune up parts, and have a dynomax cat-back system on it. I am new to jeeps in general, especially xj's and need some technical assistance. I have racked my brain and those of fellow 4x4 nuts, but can't figure it out. I even thought it might have something to do with the tranny, but I got it to do it in neutral once. Any thoughts??

Just a few things to check: Vacuum lines, egr, map sensor, O2 sensor and don't rule out a clogged cat. Good luck.

Thans for the imput Ace. I replaced the cat after some trail damage to the last exhaust, the thought of a clogged one was in the back of my mind anyway. I also replaced the vacuum lines. Thanks again!!

sounds like the Throttle Position Sensor.

90' with 55K, wow

BYM (back yard manchic) test kit

The EGR system causes problems at low RPMs, do the test from your Chiltons or FAM. The Injector system is Very sensitive to minute voltage flux, you can't test. Start with an 18" screwdriver and listen to each injector, same 'klack' from each 1. Check all wiring in the harness closley for Any imperfections. The thingy under the rotor needs to be cleaned inside and out now anyway. Also it's time to check All conectors, battery, harness', sensors, coil to body, coil/plug wires, battery/alt load tests (free at Kragens etc.) I cheat because I have Liquid Wrench and Brake cleaner on hand, it works well for connector clean up and less spensive than that fancy lectrical stuff. Next if you can afford it get the code analizer. After reading your questions,from here I would run it down to your wifes' machanic and throw it on the putter, $45-$65 and you'll find out every thing you didn't want to know. That's a good idea for everyone any way. Unless your Very old school like me. All of the above is highly recomended for 13yr o;d rigs.
Craig

since it is a 90' renix system, connecting to computer will not give you any info because it wont give you trouble codes. the best tools to use are a multimeter and a factory service manual with the renix fuel injection. i still think the problem is with the tps.

Thank you for the suggestions. A friend and myself put the truck to a diagnostic computer to find no codes. I will get down to the junk yard and pull of a tps, egr, and the O2 sensor and see what results I get. I appreciate your answers.