Has ANYONE messed with the TPS???

[EagleEye]

OK, here is what I am getting at...



On my Throttle Position Sensor (TPS) I have noticed that the 0-100% range is 'dead on' BUT the two idle switches (ON idle and OFF idle) have a heck of a lot of hysteresis. In layman's terms, it takes quite a bit of throttle to get the switches to pick up during 'OFF idle' and is real noticeable when going downhill with very little throttle.



The reason why I want to adjust the switches is because they command the Torque Converter to lock or unlock. I would like it to stay locked during these downhill moments when you are giving it very little throttle.



Has ANYONE been inside??? Before I take the plunge and take out the hysteresis on my switches (readjust) I thought I would check if there are any others 1: with the same problem and 2: people anal enough to have it bother them and dig into the TPS.



I will dive into the thing because it bugs me, but checking info before 'tearing in'.



ANY input would be helpful, and as I understand it, DC doesn't even adjust the things... just replaces them.



Thanks.

 

[Diesel Freak]

is 0% to 100% equivelant to 0V to 5V?

 

[EagleEye]

Dunno...Gotta check it

The readings I'm am getting from OBD-2 and Cummins QuickCheck both have indicated 0-100% and almost exact between the two.



I haven't measured with the Fluke meter yet, didn't take the time due to the other readings. I figured I wouldn't mess with the 'Pot' end of it. The computers seem to like where the pot is set. 0-100% OBD-2 (PCM) and 0-99% CAN Bus (Cummins).

 

[SS]

I suspect that the TPS signal is linear - that is 0V = 0%, 1V = 20%,... 5V = 100%. The "hysteresis" I think you are talking about is probably done in the software. In order to allow for "fine-tuning" at idle or just off-idle, the first 25% of pedal travel may only use 5-10% of available power. This would provide for better control when backing up trailers, low-range operation, etc. Kind of like the old cam design of carburetor cable linkage. The last 25% of pedal travel may produce 50% of available power.



I'm not sure if that is how it works - just a thought before you tear a perfectly good TPS apart. Also, do a search on exhaust brakes - I think some guys have hooked up a switch to keep torque converter locked (exhaust brakes are not recommended on auto trans).

 

[EagleEye]

Here is how I understand it...

The potentiometer is fine on mine, won't mess with that.



There appears to be 2 (may only be 1) switches that are toggled when the shaft goes to 'idle' position. These leads are listed in the Dodge manual as well as the Cummins prints for Dodge as well as the standard ISB used elsewhere.



I don't believe the computer interpolates the signal from the Pot. I believe there is at least 1 microswitch in there. THAT is what i am going for. Don't need the 'mystery' switch setup because it works. Just wanted to lower the point at which the switch(S) pick up and drop out.



When I am at partial throttle, I would like my TC to stay locked just a bit longer. If I can get to the switch(s), I believe I can accomplish this.

 

[SS]

Geez! I GOTTA get a manual.



Got me if it works as you describe. If it does sense idle with a secondary switch besides the potentiometer, then it may control more than the TC (especially if it is listed for stationary/non-auto applications of ISB). From your signature it appears you already know you may affect other things if you do somehow change the secondary switch.



I should have said earlier that 25% throttle may not be equal to 25% of fuel. Of course TC COULD be set for lock/unlock at any % throttle (and other conditions) for a given speed or it COULD use a secondary switch as you say.



Good luck in your quest. If you find it I would say you truly have an EagleEye.

 

[EagleEye]

I DID IT!!!

Got it adjusted to a much tighter tolerance. My torque converter dis-engages at much less throttle than before. It will ONLY disengage when the throttle is just a hair from the idle stop.



Things weren't done the way I expected. The TPS (APPS) is a one piece unit and the cover on it has been sealed with something VERY hard like JB-Weld. I decided to abandon the idea of getting into it and decided on a different mode of adjustment.



I needed to use BOTH computers at the same time. QuickCheck and OBD-2. I wouldn't recommend trying this at home (without the computer interface), and this excursion is absolutely not for the faint-at-heart, but if you are still interested in trying, let me know. It's really not that bad, but you need some type of interface to tell you what is going on.



Warranty?!? What Warranty?!?