1991 Loredo 138K Mi.

Thanks to all the Jeep Masters and other contributors on this forum. I'm sure that without your contributions, there's no way I'd be able to keep this sweet old Cherokee running...

Here's yet another case of TPS issues:

Several months ago, gradual onset of rough idle followed by CEL... Cleaned throttle body and sprayed seafoam through which helped for a few weeks... then rough idle came back... figured out the key-on-key-off trick... It threw the code 1-2, and 2-4, TPS. Replaced the TPS and the Jeep ran like new. I had owned it for 2 years, and until I changed the TPS it had never downshifted on acceleration. I was stoked.

Fast forward 6 months, rough idle and stalling return, however, no CEL.
Wiggle the wires going into the TPS and get a definite effect on idling.
So, I took apart the harness and found that the female ends of the 3 wires weren't fitting snug onto the corresponding male prong ends of the TPS. So I carefully swedged (a word I know from instrument repair that basically means to make a cylindrical tube narrower - like crimping, only with a lot more finesse). Started her up - totally smooth idle, and wiggling the wires produced no change.

So I thought I had done the trick to fix it.
Nope.

Test drive:
-Jeep will NOT shift out of 1st gear
-CEL is back (first time in 6 months)
-Code 2-4 is back
-rough idle is back, although not so bad, just inconsistent RPMs and kinda rough.


Next, I tried a new TPS, RockAuto's most expensive TPS. Made no difference.
Next, thinking maybe it's a bad TPS out of the box, I went to my local Parts store and tried another, their MOST expensive TPS... No dice, same issues.
Next I cleaned out the 2 Transmission harnesses with contact cleaner and air.
Nada...

What next ???
(I know what I want the advice to be, let's see...)



Thanks,
Bill

 

Engine grounds. Remove and clean.

 

Back probe the tps with a volt meter and check the voltage change as you open the throttle. Even new out of the box can be bad.
The next step after that would be to check continuity of all 3 wires from the tps to the ecu connector. Wiggle those wires around to see if the signal breaks or has a high resistance. A corroded wire can skew the voltage going through it changing the signal at the ecu.

 

Yup, did that and a bunch of other tips from Cruzer.

 

Ok, so either have 2 new TPSs that are defective out of the box, or, there's bad wire(s) anywhere in the run from the ecu...

First, the sweep test for changes in voltage...

Then continuity test all 3 wires.

Thanks, I'll post my results later today.

 

When backprobing connectors, use a small safety pin. Dont just jam the test leads in there or you can damage the connector, and possibly the wiring. Make sure the ECU connector is free of corrosion as that can give you a false reading. As will a loose wire in the connector for the TPS, or the ECU. Its not always the wiring itself, but the connection.

 

Ok, got it. I'll use safety pins and finesse as not to do any damage to wires or connections.

 

I went to back-check voltage on TPS...

Got the right numbers for pins 1 and 2, got nothing at pin 3 - ground.

Then I opened up the female plug harness by pulling back the rubber stopper at the back of the plug, and I removed the red clip at the front of the plug,

and that's where I noticed: SURPRISE... the female wire endplugs were not pushed far enough forward... all I needed to do was push all 3 of those wires forward about 1 cm. Then, push the rubber gasket/plug up tight back into the black plastic casing of the harness... and then, be sure that, when reconnecting to the TPS that the wires do NOT get pushed backwards by the pins of the TPS.

It had to be finessed back onto the pins of the TPS. Because, like I said in my original post, (I thought I was being all clever) I had SWEDGED those female wire end receptors.

So my issue went from the female wire ends being too LOOSE causing a bad connection, to too TIGHT - causing a bad connection. They had to be carefully slid back on to the pins of the TPS without letting the wires get pushed backwards inside the casing of the harness.

So now, they're Goldylocks... JUST RIGHT.

I had lost confidence, and I was frustrated. Thanks you guys for helping me.
Without this forum, I'd be effed.

I figure I got lucky this time... alls it cost me was a $29 TPS and a $35 TPS.
I have 2 extras now. If anybody needs one let me know (PM). I'll send them for the cost of postage.

Thanks again.