My jeep is a 90 xj with the 4.0l and it is having a strange problem that seems to have started out of no-where... While out playing in the mud the engine went from running great, to bogging, burping and backfiring with any throttle input, the engine idles totally normally, but when i tap the gas, it boggs down and starts to sound like death.
So far i have checked/ replaced
brand new fuel filter
brand new fuel pump
brand new tps
Checked timing ( was fine at idle)
Checked for blown fuses
Checked for any vacuum leaks using starter fluid at idle
the cap, rotor, plugs and wires are 1 week old..
Probed the trottle body flap and visually checked for proper movement

...none of this has done anything to change the symptoms.. take a look at the short vid for visuals and audio
http://i13.photobucket.com/albums/a254/Fumihiko2/cars/th_jeepburp.jpg (http://s13.photobucket.com/albums/a254/Fumihiko2/cars/?action=view&current=jeepburp.flv)
Thanks in advance for any help!

You were playing in the mud. Did it sit in mud or water at all, as in if you were stuck?

nope, with it not going over 1000rpms i still managed to pop right out of where i was

Might try checking the CPS connection, that can make it run like crap.

cps connection?

cps connection?

Crank Position Sensor on a 1990. The newer blocks have a Cam Position Sensor as well, I've been working on my 05 block and both sensors are on my list of possible problems.

oh gotcha and i'll check it really quick i know right where it is

checked the cps and its still plugged in and in the correct spot.
is there anyway to check the actual sensor?

checked the cps and its still plugged in and in the correct spot.
is there anyway to check the actual sensor?

Might want to pull the plug and clean it out. Those connectors are pretty famous for going bad.

There's a great arcticle here about testing sensors on a Renix era jeep.
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

awesome link thank you.

I cut of the plugs, and soldered the CPS to the harness. I also installed an inline switch that runs under the dash so I can turn the CPS on or off. I hope that if somone tries to steal my MJ...it will discourage them.

Check the map sensor vacuum. I had a similar thing happen and it was unplugged. It idles great and runs like shit when the vacuum line broke

Code reader of the higher value should display all the ECU values for each sensor, to tell you if it was working or not. This does not tell you if it's working correctly, so it just eliminates half of the possibilities.

Try checking you MAP sensor plug on the leftside of your Throttle body..

coused mine to run like crap also

Code reader of the higher value should display all the ECU values for each sensor, to tell you if it was working or not. This does not tell you if it's working correctly, so it just eliminates half of the possibilities.


What kind of code reader did you find that does that with a Renix system?

Check the map sensor vacuum. I had a similar thing happen and it was unplugged. It idles great and runs like shit when the vacuum line broke

Definitely check the MAP vacuum line. It runs from the passenger side of the throttle body to the sensor on the firewall. If it is loose or broken it will run like crap.

You may also want to clean your throttle body and throttle position sensor.

Sounds like textbook throttle position sensor. If you have autotrans, you hook a DMM to the square connnector between terminals B(+) and D(Ground) and you should have 4.15 volts. Then open the throttle plate and if the voltage drops off at any point you have a dead spot. For the manual trans, You connect the DMM to the only connector that comes out of the TPS between C(+) and B(Ground). The voltage should be .85 Volts. Open the throttle plate and watch for uniform drop off of voltage.

i found on my 89 it would ideal good and high rpm good but midrange would
backfire and pop. replace all sensors, dist. , coil. last thing i replace was the
injectors. fix all my problems

Sorry to drag up an old thread guys, but does anyone know if this guy got his rig fixed and what the problem was?

I have the exact same problem on an 89 XJ and have been working off and on on it for over a year. (Yes, I've already checked Naxja, there's an ongoing thread.)

Thanks y'all.