90 XJ AT shifting / TPS problem

Hello Bill, I took a look at that info earlier today. His diagram of the TCU is 180 out from mine.I did check the fuse, cleaned the connector and verified 12v to the TCU. I figure since I do have decent input voltage to the TPS and the output is way off it has to be a bad TPS . The only thing between the input voltage and the output voltage is the TPS internals, unless I'm wrong which happens alot (that's why I posted)

The TPS on my XJ has 2 pigtails one sends a voltage signal to the transmission controller. The spec for the TPS output to the transmission controller is about 4v, if it's only putting out .34v wouldn't that affect the tranny? I had the same problem 4 yrs ago and a new TPS was the fix.

Thanks, JK

Your readings don't sound right to me...

With the engine off and the key on run, the AC off, you should see a

0.026 volts. When you open the throttle all the way, you should see 4.8 volts.

The TPS for the auto should have the second output which should be the inverse of the above readings as far as I know. 4.8 V at the idle position and 0.02 V full open.

You also can take an ohm meter and read it as the throttle opens. It should change smoothly. If it is jerky, the coil inside the TPS is dirty or bad.

On your 90, I think the TPS is adjustable for the bottom end or the .02 volts. There should be a capped screw like a mix screw on a carb.

I have been told you can actually clean the guts of the TPS, but haven't needed to yet.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

Your 90 I think has a RENIX system and the TPS is adjustable. Have you adjusted it? Also as I recall the readings for a auto are different but I don't remember for sure.

JoBo

Hello, yes I adjusted it, it won't adjust near far enough to get a proper reading. The readings from the AT plug are .35v at idle and .01v wide open. The readings while opening throttle are smooth. The ground reading of .8v has me thinking I should splice a ground to the circuit, this was recommended in another post. I did check chassis to block grounds and I did the old jumper cable check with no change in reading. Thanks, JK

Well I guess it's not the TPS, just put in another new one and get the same readings. Could the TCU affect the output voltage of the TPS?

I pulled the fuse from the TCU and it shifts fine manually, also took some readings at the TCU and they are way off. I guess a bad TCU? The link that Bill gave has some great info on checking the TCU but I was looking at it backwards and thought it was 180 out. The guy also says at the end that if the readings are within spec the TCU is a transmission condemed unit, I'm thinking he meant out of spec.

Or he was meaning if it checked out ok, the tranny was condemned?

Do you have a transmitter on board by any chance? I know that a transmitter can cause the TCU to have total brain farts if the wiring or antenna are anywhere near it or it's harness.

On the 90, the ground still jumps out screaming at me....

I think I would run a dedicated ground jumper to the TCU just to see what happens, same for your ground jumper idea on the TPS ground.

A lot of the computer grounds terminate on a bolt on or near the oil dipstick. There will be a bunch of small black wires bolted on there. That might be worth a clean too.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 (More Off Road album links at bottom of the view page)

It was the 2 big connectors that go to the AT, one grey and one black right by the AT fill tube. I cleaned them up with contact cleaner it now shifts perfectly. I spent two days trying to figure it out. Thanks, JK

If it gets below 3, yeah. 3.4 isn't that much off from 4. An old battery could cause that minute difference and your tranny would still work. It'd also still work right at almost 5 volts.