Jeep xj surging

[Bmfinney]

Guys my Jeep is a 4.0 aw4 transmission. I’m trying to diagnose an issue. So driving down the highway cruising in overdrive everything is fine but when I start going up a hill and I put my foot down and it downshifts the Jeep starts surging. What could cause this? Driving around town everything is good.

 

[Bmfinney]

Any of you guys have an idea?

 

[RCP Phx]

What year? Maybe the fuel pump failing?

 

[Bmfinney]

It’s a 96 yeah I was kinda leaning that direction. I don’t have a fuel pressure guage to check it. I’m gonna have to get one to see if that is it.

 

[75SV1]

How many miles? Check the distributor shaft for play in it.

 

[Bmfinney]

It has 197k it runs good for the most part it’s only on highway speeds when downshifting I have a feeling this is gonna be a pain in the a$$ to figure out.

 

[75SV1]

Just a guess, but the speed sensor on the transmission. ???

 

[Bmfinney]

Possibly I will check that as well and keep y’all informed I have been messing with the cable on the throttle that goes to the transmission that might have something to do with it as well

 

[Anak]

Just a guess, but the speed sensor on the transmission. ???

I would expect the speed sensor issue to also show up on the speedometer. I had an issue with that in my Cummins (which I believe uses the same sensor). My speedometer would fluctuate and that essentially rendered my cruise control inoperative. Being a 12V Cummins there was no impact on the engine fuel/timing parameters, but it sure showed up if I tried to use CC.

FWIW, I was able to fix the problem by simply pulling the sensor and working the input shaft. Somehow it got sticky. Might be related to several hundred thousand miles. I may have used a silicon spray lube or something like that. It has been a while. At any rate, I got it freed up so it would spin smoothly again and that solved the problem.

 

[Bmfinney]

Well my speed sensor has been acting up lately. I didn’t think it affected anything but the guage?

 

[Anak]

If the speedometer is acting up and the engine is surging I would take care of that sensor.

It is an easy sensor to pull, but before you pull it pay attention to how it is clocked. IIRC clocking is how you cope with the various gear sizes.

I would pull it and check to see if it spins freely. If it is how my Cummins was it will vary in resistance as you try to spin the gear. If it is doing that, then try to lubricate it and get it to spin freely. If you can do that you may end up fixing your problem for just a bit of effort.

 

[Bmfinney]

Well long story on this. The rear driveshaft was worn out cause of the vibration that I had. I thought it was the rear axle. But no. It was also throwing the speed sensor off like you guys said which was causing the surging. I put my front driveshaft to the rear and it fixed everything.