Engine/Transmission (1994 - 1998) TPS or Lock up Switch

[wrichards]

I am sure this has already been asked but I am having trouble with TPS locking and unlocking converter. I sprayed with contact cleaner and it seemed to help for a few days but is once again locking and unlocking unable to find proper speed/gear. I would like to install a lock up switch so I can decide when to lock and have read posts about a 3 position switch so it can be in normal drive mode as well in case my wife needs the truck. Can you help with instructions. Does anybody make a kit for this that includes everything??

 

[Bob Wagner]

it may just be electrical interferance, try cleaning the battery terminals and also checking the grounds.



I would also avod the mystery lock up switch it can cause transmission suicide with operator error

 

[Joe G.]

Bob is right. You can break things if you don't use a lock up switch properly. I've used one for about 140K miles and, so far, have not managed to break anything. If you would like the wiring details e-mail me.

 

[Howard Durand]

The "Mystery Switch" is not a substitute for a properly operating TPS.

Check the numerous posts concerning TPS problems. You will find that the most positive fix is to separate the TPS wiring from the rest of the wiring in the harness.

One of the members has come up with a kit that will replace the existing TPS wiring with a shielded pair. Is selling it for about $39.



As for the mystery switch, the 3 position switch gives full control of the TC. (locked, unlocked or normal)

It requires cutting the wire going from the PCM to the TC lockup solenoid and bringing the ends into the cab for attachment to the switch.

 

[Dave Remillard]

You mentined cleaning the TPS. Just wondering if you checked the voltages also? May be as simple as an adjustment. However with some of these, once this problem gets going the only fix is what shendren did. He is the one with a kit to replace the wiring to the TPS. Do a search and Scott has plenty of experience with this problem and found the cure.

 

[Gifford]

TPS

I tried the cleaning methods suggested on the forum, didnt work for me. I bought a new one from Cummins, easy to install and problem went away. (TPS)

 

[Dennis Garrett]

I don't know if my TPS is working or not, I put in the three pos. switch almost 200k ago when I first got the truck, and drive it by the switch 100% of the time. I've never given it a chance to do very much on it's own. Nobody drives it but me, and I use it so automatically, I fish around for it when I drive other vehicles! I have mine mounted about an inch below the turn signal lever. Like the other post said, CUT the wire, & run both ends to the switch, wire one to the center, the other to an end, wire the other end term to a ground someplace. On my 97, I had to also take out a transmission relay in the fuse box under the hood, and replace it with a jumper, not sure about 95's

 

[shendren]

yep, i tried everything. i didn't like having to use a lock up switch in the cab. i just think a $20,000 or more truck should not have to be tinkered with so much to get it to run right.



i just rewired the tps and everything works fine now. howard's right. the kits are $39. sold a bunch in columbus, indiana this weekend... ... ... . the local dealer is even happy!... ... .



pm me if you need one.

 

[Dave Remillard]

Scott... . Do you have any photo's of your kit installed? Just might encourage some to purchase the kit if it looks easy enough.

 

[shendren]

yes, i can take some pics. not much to see except wire loom. i'll post them... ...

 

[shendren]

can't see much... .

 

[shendren]

woops... ... ...

 

[shendren]

another

 

[shendren]

as you can see, i had a bunch of wire left over. pre-kit installation. i just zip the new loom to the firewall. the kit includes a sketch and instructions.

 

[shendren]

off the subject



but i took a photo of the fuel press connector that i used. no ferules. doesn't even think about leaking... ... ..... !!

 

[shendren]

she got in my way... ... ... my helper... .

 

[JohnE]

The regular mystery switch or TC lockup control is manually locked or PCM controlled if you follow the TST instructions.

The 3 position switch is nice if you want to keep the TC from locking by PCM command.

 

[Howard Durand]

I like the three position switch.



I use it primarily for locking the TC to permit use of the exhaust brake. I also use it to unlock when I need to get the rpm up.



To prevent OD shifting while the TC is locked up I built a circuit that disables the "Mystery Switch" for a few seconds whenever the OD switch is pressed. That allows the PCM to control the TC and OD normally. When the circuit times out, control is returned to the Mystery Switch.