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Have to shift manually shift Renix tranny -> Bad TCU ?

blondejoncherokee

NAXJA Member
NAXJA Member
Location
sacramento
1989 XJ with AW4 .

basically in D it starts in 3rd. same in 3. in 1-2 it starts in 2. My little tranny switch thing still lets me force it into 2nd gear. Trying to get 3 and D to work in all gears again.


I swapped and calibrated the TPS - same as I have been doing for years, I usually have to do this twice a year or more so I know how to set and calibrate it. It usually fixes any tranny related issues.

I checked both tranny fuses- the one at the box and the one inline near the TCU - are there any others?

I cleaned the bulk head connectors near the oil dipstick.

I cleaned my grounds for fun and also drained and filled what was in the pan. The fluid was a little dark but I change the fluid out of the pan(not a full flush) 3X a year.



Any ideas? I am thinking of swapping TCUs at this point? Or would a solenoid do this?
 
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Check the solenoid resistances at the tcu. If one is open, it will show. Refer to the diagram for your year for pinouts. I can see an open solenoid throwing it into limp home.

Hth.
 
Did you volt test at the main TCU connector? If a fusible link went out you'd likely have more problems than just the TCU, but the splice could be bad. The yellow wire from the ignition switch and the red wire from the fusible link are the important ones.

I've had the pins back out of the TCU connector on numerous XJ's. Hold the connector and gently pull on the wires individually.

Ohm test the TCU ground.
 
Did you volt test at the main TCU connector? If a fusible link went out you'd likely have more problems than just the TCU, but the splice could be bad. The yellow wire from the ignition switch and the red wire from the fusible link are the important ones.

I've had the pins back out of the TCU connector on numerous XJ's. Hold the connector and gently pull on the wires individually.

Ohm test the TCU ground.

where would this fusible links for the TCU be located?
 
where would this fusible links for the TCU be located?

The fusible link is hooked to the starter relay. I'm pretty sure the same fusible link is for the fuel relay also, so if the motor is running it is likely to be good. But there may be a problem between the fusible link and the TCU. Something to look at before you swap parts.

A quick test is to volt test the red wire at the TCU connector. A significant voltage loss can indicate what Cruiser noted, some sort of resistance in the circuit.

You not only need volts, you need amperes. Low voltage (pressure) readings indicate a resistance or a significant drain (partial short someplace), which lowers current flow (amperage).
 
My bets would be on either the TCU or the NSS.

I would also remove your switch setup and see if all is fine. IIRC, to hold it in first gear, it actually removes the power from the TCU. A busted wire would render the TCU non functional.
 
TCU fuse location. Also keep in mind the TCU grounds at the engine dipstick tube stud.

TCU%20fuse_zpsstra8x6z.jpg
 
yeah I checked that fuse first. I will check the tranny wiring and swap the TCU out and get under there with the volt meter.
 
If you take the knee panel off of the dash it gets a lot easier to do your troubleshooting.
 
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