Hi guys have a 2000 xj 4.0 classic,having an engine surge problem,on the highway at 50mph rev counter drops and raises,causing down and upshifts ,i had a problem like this a few weeks back and traced it to a vacuum pipe off the inlet manifold,replaced it and all was well.Cant solve this one and its driving me nuts,today i sprayed carb cleaner around the manifold but couldnt find a leak,so could it be something else? would really appreciate some advice...

 

The first thing you should do is get it scanned to see if it is putting out any code or if it has any codes stored. That would at least give you someplace to start.

 

Thanks for the reply,Scanned? can you explain that to me,and where do i see the codes? just getting to know this truck bit by bit so sorry for my ignorance..

 

If the check engine light is on, the orange engine shaped light on the dash, then that means the ECU has detected a fault of some sort. Most auto parts stores (Autozone, Advance, etc.) will plug in a code scanner, and read the info from the ECU to tell you what caused that fault (or a general idea anyway).
edit: sometimes it's NOT on, and the ECU stores the codes. Check it anyways.

Does the engine do this at any other speed? Try having the transmission in "3" instead of "D" and see if it does it still.

 

Thanks,understand that now,i have no light on though,does do it at slightly higher speeds also,il try it in 3rd tomorrow on way to work,why would that make a difference? and if it does what is that telling me..? appreciate your help..

 

well drove to work using 3rd and still doing the same thing...

 

I would take the transmission of the equation now. I'm still thinking a torque converter issue MAYBE...

If you have a smartphone, maybe make a small video and post it up to youtube for some visual reference.

Aside from a vacuum leak, which when the engine revs (from the extra air) that tells the transmission to downshift. Perhaps the TV cable is loose or out of adjustment?? Or even the throttle cable.

 

Do you think i could have disturbed something during the fitting of my 3" RC lift kit? just such a weird coincidence its running poor after driving her out from the lift..just clutching at straws now buddy....

 

Does what you are experiencing look like this???


This is my Jeep heading off to work. Is it similar?
Edit: Speed unchanged but RPMs shifting?

 

Mine drops a full thousand RPM???? changes down a gear then backup??

 

That is definitely a full gear change with 1k RPMs. No change in speed, right? I'm just at a lost as to what would trigger that. Did you readjust your TV cable and double check the connections on the transmission? Fluid level ok? Install a slip yoke eliminator kit when you lifted?

On my Ranger, when I rebuilt the transmission, I broke a tab on a connection, and that kept my torque converter from locking up. Perhaps something was pulled off/not seated all the way.

 

No I didn't fit a SYE I am gonna fit a Transfer case drop though,would the angle of the rear prop maybe be a cause for this do you think? its only a 3" lift and all iv read here suggests a SYE isn't required, Would the prop pulling slightly out from the rear of the gearbox cause this? being the angle is now obviously more extreme than when standard,thanks for all your advice buddy really appreciate the help,and what is the TV you referred to...