88 AW4 questions

88 cherokee, aw4 trans, ~ 360k on the ticker, aftermarket tach.

Just checked the TPS readings today, cuz my trans is taking way too long to downshift. You almost have to have it to the floor to get it to kick down. MPG is also way down, and I wasn't sure if it was trans related or not. I can't see going from 30" to 31" cutting mpg down by 40% on the highway, but rpm hasn't really changed for the same speed (< 100 rpm), so I am thinking something ain't working right Kickdown cable is adjusted properly / by procedure

TCU side of the TPS
A - D - 4.5 v
B - D - 3.6-3.7
d - neg post - nothing

ECU side
A - B - 4.9 v
B - C - .8 v
c - neg post - 2.4 ohms

I think I need to adjust it so the TCU side B-D is 3.7 solid, but the lack of a ground on the TCU side has me thinking I need a new TPS.

I also got some weird readings a couple of times, like the A-D & B-D readings were swapped. This was after I tried adjusting the TPS.

Would replacing the C-101 connector help with any fo thsi, maybe help obtain a better ground ?

C101 should always be cleaned out til shiny and all crud removed. Spray out with a good electronics cleaner. Add dielectric grease and bolt back together.

There is a simple test for the ground circuit which affects not only the TPS but the IAT, MAP, and CTS.

PM me your email address and I'll send you the instructions for the TPS that also include a 20 second test of the sensor grounds.

For some odd reason (IIRC) the TCU side of the TPS has different ground line than the ECU side. I had similar problems, but mine was a bad TCU ground, bad TPS ground on the TCU side and a bad TPS. Try running a new ground wire from the TCU side of the TPS to the battery. Also check the TCU ground wire on the TCU!!!!

And the write up Cruiser54 has should be followed as well.

EcoMike....one of your old posts is what got me to checking the grounds.

What I couldn't figure, is the black wire (D) coming out of the TPS for the TCU, and the black wire coming out of the TPS for the ECU are not connected (or at least aren't on mine).

That's why I was wondering if my TPS is bad or not. It's at most 2 yrs old


Cruiser54.......IM sent....Thanks !

TRCM said:

EcoMike....one of your old posts is what got me to checking the grounds.

What I couldn't figure, is the black wire (D) coming out of the TPS for the TCU, and the black wire coming out of the TPS for the ECU are not connected (or at least aren't on mine).

That's why I was wondering if my TPS is bad or not. It's at most 2 yrs old


Cruiser54.......IM sent....Thanks !

Click to expand...

You need to check the ground using ohms, with the TPS disconnected. That way you are testing just the wiring harness ground wire. IIRC the TCU and ECU grounds on the TPS are two separate grounds. They are probably grounded through the TCU and ECU separately. I ran a new ground on both directly to battery negative post on mine, using a splice to add the grounds, leaving the old ground wire still attached. It solved a lot of problems for me. Cruiser solved a lot problems with his recent method which is in the write up.

Ecomike said:

You need to check the ground using ohms, with the TPS disconnected. That way you are testing just the wiring harness ground wire. IIRC the TCU and ECU grounds on the TPS are two separate grounds. They are probably grounded through the TCU and ECU separately. I ran a new ground on both directly to battery negative post on mine, using a splice to add the grounds, leaving the old ground wire still attached. It solved a lot of problems for me. Cruiser solved a lot problems with his recent method which is in the write up.

Click to expand...

They are separate. Probe the brown with white tracer wire at the flat connector of the TPS with your meter set on OHMS. Place the other probe on the negative battery terminal. Get your reading. Then, wiggle the engine harness along the valve cover and over near the MAP sensor. See what the meter reads and report back.