90 MJ 2.5 AX4 bucking issue

[Kikendallmd]

Ok gents,

  here's the backstory. Rebuilt the engine last year. NEw everything. Jeeps been running like a champ for the past year, no issues. Lived in nice warm sunny Florida, used it as my daily driver. Moved to Missouri last week. This morning it was 20 degrees, had to make a 30 mile drive to town for a job interview. Started fine, ran good for about the first 15 or so miles. Then started bucking when under load. Didnt matter which gear. Turned it off for about 30 minutes during the interview. Started up great, went to the gas station got fresh fuel. Ran fine. Plenty of 2.5L power, until I drove it at highway speeds for about 15 miles on the way back home then started bucking again. Anything over about 1/4-1/2 throttle it bucks, and my REM scanner said lean open fault loop on the uphill portions when it bucked... I don't have the exhaust to air box heater hose hooked up... My only idea is the TBI is icing up maybe? Any ideas?

Oh- O2 sensor is doing the flip flop like it should, until I started going up hills then the lean fault kicked in. 

[cruiser54]

Have you performed any of the Tips at www.cruiser54.com?

 

The braided ground wire at the firewall can cause all sorts of issues if it isn't in tip top shape.

 

did you get the job? 

[eaglescout526]

This issue makes me think TPS. I’ve had it to where I would be driving and I’d get the same thing where it would hesitate and buck and go back to normal driving until it acts up again a few miles later. Found it to be TPS as that’s what tells the ECU to more or less dump fuel. 

[Kikendallmd]

Cuiser54- Yeah I did everyone of your tips when I initially did the restore/rebuild last year. Actually I hit you via email a couple times.

Eaglescout- Not sure on the TPS- I was watching the REM and saw the TPS sliding back and forth around the right amount when I was driving on the module.. Not saying its not, but Ill def. give it a look and exam in detail..

Check FP- noticed when the pumps not running, the pressure almost immediately goes back to zero- Do the renix 4 bangers not have a pressure check valve in the pump? When its running, the pressure was spot on 15psi, although for the first minute or so it jumped around a bit... Air in the lines maybe.

[eaglescout526]

Check the TPS. The TBI has a pressure regulator on the body, if it hasn’t been serviced, it could be failing but don’t suspect that right away as that’s a full day job to rebuild the TBI.