Engine/Transmission (1994 - 1998) TPS saga continues

[JamesPhillips]

Okay. I bought the wiring kit from Shendren and rewired the TPS. This worked for a few weeks. Now it has started the same problem again. Around 40 - 50 mph, the transmission starts hunting between 3rd and overdrive. Do I replace the TPS now?



James Phillips

96 2500 2wd ext. cab longbed automatic

 

[DMC]

Try pulling up on the brake pedal. If this helps let me know.



Don

 

[mstimac]

Have you actually taken apart the TPS and cleaned the wiper arms? I did it to mine darn near 70,000 miles ago and have not had a problem since. Once you take it apart you'll see why it gets noise it the circuit.

 

[LHartman]

What mstimac said. Mine was hunting like that last week. I took the TPS off and hosed it out with Electrical Parts Cleaner. It was pretty gummed up. Works like a champ now.

 

[mstimac]

Actually I took it one step further and did the same as Jim S shows in his thread. Here's some pictures from the past.



https://www.turbodieselregister.com/forums/showthread.php?threadid=37289&highlight=tps+cleaning

 

[JKouzez]

i just did the little switch trick very easy makes the truck a little quicker too.

 

[cskdoug]

Mine was doing something like that. I found the spring on the drivers side of the trans linkage was broke. I installed a new one and it fixed it.

 

[rx7pat]

tps

Mstimac thank you for posting the pictures of your fix did mine today the difference is unbelievable

 

[Dfuruness]

I just replaced it and no problems. That was 5 years ago.

 

[mstimac]

rx7pat,

Your welcome, but I can't take credit for the fix. Jim S. actually posted the pictures, I just did it the same way he did then dug up the old post for eveyone else. Glad it worked for you!

 

[Howard Durand]

James Phillips,



Since you have eliminated the electrical noise problem with the by-pass wiring kit, have you checked the voltages at the TPS?

The signal voltage with the trottle closed should read 1. 0 volts

plus or minus . 2 volts and smoothly increase to between 3. 5 and 4. 5 volts at wide open throttle.



Also, have you checked the transmission throttle linkage adjustments?

If your truck has had the throttle cable replacement done under the recall, lord only knows where the dealer set it.

If you have a manual, it should show how to set it correctly.

Make sure the throttle return springs are all connected and in good shape.



Make sure the contacts are clean where the engine speed sensor plugs into the wiring harness.



As DMC said, check the brake light switch.

A new TPS is expensive, so clean it if you can. Replacement should be the last thing you try.

 

[sadams]

Yesterday I had the wire harness replaced with Shendren's rewire set (which is very handy & nice) and hoped today, on its first trial through the canyon at 35-40 mph I would not have the slipping in & out from the TC, however, there it was again. Very discouraging. Thanks for this tread as now I can try a few more things and see if that works. No one has ever talked about "adjusting the bands" on the transmission. I'm assuming that means when I had it served they couldn't have screwed that up, right?

 

[Joe G.]

I've always felt that the business with pulling wires out of the old harness and installing a new wiring harness are just bandaids for the real problem which is a dirty TPS. So far, just giving mine a shot of contact cleaner everytime I change oil has worked. If that fails, then I will use the Jim S. method to clean it.

 

[BigPapa]

What Dfuruness said. I replaced my TPS 95K miles ago and haven't had another problem since.

 

[Howard Durand]

Noise can be generated by devices in the electrical system and coupled to adjacent wiring in a wiring harness.

Since the TPS circuit is one that is most sensitive to voltage fluctuations, it does make sense to isolate the TPS wiring.

What probably makes more sense is to find the source of the noise and fix that.

My 94 has never given me any trouble other than a few times that it did drop out of OD for no apparent reason. That happened when it was new but hasn't occurred in the past few years.

In the 94 models and possibly the 95's the 5 volt source for the TPS is fed with a dedicated wire directly from the PCM but in the later models, that same wire carries the 5 volt feed for the Engine Speed Sensor as well which, in my opinion, increases the possibility of noise coupling to the TPS.

Probably the best way to test the TPS would be to connect a scope so the signal could be watched while the truck is in operation. I don't have a scope and probably couldn't figure out how to hook it up anyway but I'll bet there are people who can.

Considering the cost of a new TPS, it would make sense to try everything else first.

Another thing to consider is that ground wires can be a problem too if they are not solidly connected.

The grounds for all of the engine sensors are connected together at a bolt in the head at the front of the engine on the driver's side. Make sure there is no corrosion and that the bolt is tight.

 

[sadams]

Well, I think the TPS problem is fixed now. Last night we took the TPS off and just used the contact spray on it and put it back on. (Did not take it apart), today was my first run and where it was slipping in and out at 35-45 mph on the hills, there was no slipping at all for the first time since summer. Feels great, hope it stays this way. Thanks for all the suggestions and help.

 

[Howard Durand]

Outstanding!!!

 

[sadams]

Thanks for the voltage info Howard. After we cleaned the TPS, my boyfriend put the truck on the computer and checked the voltage also to make sure the TPS was not bad and it did exactly like you said, showed 1. 0 at idle and increased with opening of the throttle to 3. 5 to 4 and showed normal working. I guess these TPS devices can be saved with cleaning! Mine is the orig. 1996 one but only 85K on truck.