3tonexj

New to the forum, but have been reading other members posts for the last 2 years to help me diagnose my own xj problems. Thanks to all who have pointed me in the right direction in the past.

2000 xj classic-4 inch lift-everything else is stock.

Here is my current issue....
about a month ago as I was leaving my driveway, I noticed my check engine light was on, then all gages dropped to zero followed by gages coming back to normal except my volt meter pegging at 19 volts. At this point the tach sticks at about 800 rpms regardless of how much throttle is applied. When under load, the Jeep backs normally but in drive I have to run the rpms up to get it to move, almost like the tranny is slipping, but reverse is normal. Fluid level is ok in tranny.
This seems intermittent as I can drive for several hundred feet with everything normal until I hit a few bumps and this starts. It will sit in the driveway at idle all day long with no issue.
Originally I suspected a charging issue, but now the transmission issue has me stumped.
What I've done:
-Checked voltage at battery while this occurs...19 volts at battery and on dash volt meter.
-Had battery and alternator checked at 2 different auto parts stores...alt checked good at both places, battery checked bad at 1 and just needing a charge at the other store. Trickle charged the battery...no change.
-Replaced battery and sepentine belt.
-Removed and cleaned (to bare shiny metal) grounds/connections at back of alternator, both battery terminals, battery (-) to fender, firewall to engine, negative to engine block (passenger side), positive to starter, positive to fuse block in engine bay, ground by oil dipstick and ground just forward of it also.
-Replaced ecu with a refurbished unit (unlikely but just in case).
-Pulled codes off computer (P0715), swapped ecu and read again...same code. Cleared code.
-Inspected harness for shorts/damage. None viable.
-Wiggled as many wires and cables as I can find with engine running and VOM connected to battery trying to reproduce the fault...no joy.

Every thing I've read, I've tried....the tranny thing has me baffled, but electrical gremlins to strange stuff.
Needless to say, I'm just about out of ideas and I detest the idea of actually paying someone to fix this thing.
Anybody have advice or thoughts of where to look next?....Anybody...please?

Bugout4x4

Two thoughts here. First I am pretty sure it should never be showing anymore than 15 volts. And your code is for the speed sensor but it might be making the ECU go loopy. I hope some more chime in on this.

3tonexj

Agreed. At idle I'm reading ~14.6 volts at the battery. I checked both the old and refurb ECU to verify the code wasn't just stored in the new ECU. Read in another thread (same issue and symptoms) about p0715 being an errant code, so I cleared it. It hasn't returned...yet.

Bugout4x4

14.6 is normal, but if it is going up to 19 at anytime, I would say the alternator regulator is having issues and could cause side effects related to this.

3tonexj

That was my thought too. External voltage regulator in the ECU. Not a common failure but I swapped it out for a refurb anyway. Same symptoms with either ECU.

Bugout4x4

Hold on and let me do some digging.

Bugout4x4

Here are three possibilities. If the field coils in the alternator are shorted inside it will do this. And the A22 connector going into the ecu must be receiving at least 10 v or it tells the alternator that there is a low voltage situation which causes it to overcompensate. or the battery temp sensor has issues. The old ecu may be fine. I would check to make sure there is no short or other cause like the battery temp sensor preventing at least 10 v from coming into the ecu at the A22 connector when the condition is presenting it's self if possible.

Now I'm just guessing here and hope maybe someone more knowledgeable can share more.

4.3L XJ

If you have a bad speed sensor, say a short it can affect the ECM to such a degree that it will not run. Have a friend with a 99 that had this happen. Replaced speed sensor and all is well. I am going to theorize that any alternator problems, which the ECM controls, are being caused by the speed sensor. I would replace that first and go from there

Willys55

3toneXJ...............I edited your title.

Titles that start as "help"....."what next" ...."What is the problem here"....etc. hardly ever get the attention of someone that might be able to help.

Suprmn

When you put it in drive and start to go, manually pull it into first gear and see if it shifts down and starts to move out normally.

3tonexj

Where would I test A22 at?
I pulled out the battery temp sensor and inspected...the wave washer was intact but I didn't ohm it so ill check that as well.

3tonexj

That's a very interesting theory....maybe I've been looking at this all wrong from the start. Ive been thinking this has been a charging issue with the transmission slippage as a secondary effect. Do you know where the sensor is located? If I have a general idea, it'll save time crawling around on the still nearly-frozen driveway!
I grabbed a sensor at AZ today but probably will not be able to look at the jeep until tomorrow morning. Hopefully its a match....

3tonexj

Thank you sir. I'm new to the forum. I usually ghost in and out, get the info I need without adding any of my own knowledge. Ill be sure to chip in from now on if I can help some other poor soul.

3tonexj

I'm gonna try that later tonight. I hadn't really considered this a primarily transmission issue until now. I checked all my fluids a month ago the day this started, but I'm going to start from scratch with the tranny.....fluid color/smell/level and go from there.

Eric Coyle

My 95 jeep zj with 5.2L automatic transmission 35 in tires slips after driving 10-15 minutes I shut off let sit for a minute and I can drive it again sometimes for 100 feet sometimes miles please help