Topic: TPS testing

[oldjeep]

ANy idea how to test the TPS on a jeep throttle body? I've finally got the AW4 wiring done for the TCU, got it going and it wouldn't shift out of first. Looked at the logic diagrams for the Trans control and decided to unplug the TPS which is one of the things that the TCU watches. All the sudden it shifts fine.

One of 2 things is wrong here - either I have a bad TPS (PCM didn't seem to care that it was unplugged) or I wired the TCU to it in-correctly.

So to start, I'd like to make sure that the TPS is good.

[oldjeep]

This is in a 94 2.5L YJ that used to have an AX5

[wrangler387]

One of the wires should have put out a linear voltage depending upon how open the throttle is... I think its like .5V to 5V???. I'll check megasquirt alittle bit later and see what the reading is. Then one is a ground and i think there is a constant source also. So i guess use your volt meter and start checking.

[oldjeep]

According to the diagrams I have the 3 connectors are Ground +5V and sensor output.  Do you happen to know if 5V is full throttle or closed throttle?

[wrangler387]

full throttle will be the higher reading... let me go bring the laptop and see what my reading is on megasquirt.

[wrangler387]

need an edit button.... Alright, i have no clue as to what the voltages are... I don't remember how i set it up, megasquirt only displays what percentage open my throttle is. But i think it is less then 5V, because i had that in my head from when i set-up my wideband o2 sensor. Basically make sure that the one wire displays different voltages as you open and close the throttle. Sorry for not being to helpfull.

[Jesse-James]

Shouldn't be hard to tell with a meter anyway, check all three and see which voltage changes to figure out which one is the output. If it's bad it usually wont be completely dead, you usually just see a dead spot as the the voltage changes with throttle position.

[oldjeep]

Doesn't appear to be anything wrong with it.   I took the one on the jeep and another one off a 4.0L throttle body and measured the resistance.


Closed Throttle Signal with - ref  was 100 Ohms on one and 400 Ohms on the other
Open Throttle Signal with - ref  was 5K Ohms on one and 5.85K Ohms on the other

Closed Throttle Signal with + ref  was 5.5K Ohms on one and 5.7K Ohms on the other
Open Throttle Signal with + ref  was 540 Ohms on one and 460 Ohms on the other

I may have the signal refrence backwards on the TCU hookup.  Need to look at the drawings some more.

[Jesse-James]

Did you measure as you moved from closed to open, or just full open/closed?

[oldjeep]

Just closed to full, wasn't really looking at the intermidiate results.  However the jeep was not shifting no matter what position the throttle was in when I had the TPS hooked up.

[Jesse-James]

Not too familiar with the tranny computer, I was just thinking it might be looking for a certain output voltage and that spot being dead on the TPS. For example if it wanted to see 3.5-4v and it was dead in that range it wouldn't matter where you had the throttle. My electrical background is industrial machines so my thinking may be a bit off here.

[oldjeep]

I think I found the problem.  The wiring diagrams that I've been using for the AW4 are from a 94 FSM.  The TCU I have is from a 1990 2.5L XJ. 

I posted on NAXJA, and someone had a 90 FSM online.  Looking at the wiring diagrams, it appears that the TPS signal on a 1990 (Renix) is backwards from the signal on a 94.  The 90 TPS has 2 connectors, one which sends 0-5 to the ECU and one that sends 5-0 to the TCU.

The way I have it wired, the TCU is expecting to see 5-0 volts and it's seeing 0-5 volts.

Easy enough to reverse it and find out I guess.

[Jesse-James]

It would be nice if it were that easy. Every difficult problem has a simple solution, it finding the simple solution that's the difficult problem.

[oldjeep]

It would be nice if it were that easy. Every difficult problem has a simple solution, it finding the simple solution that's the difficult problem.

Unfortunately it's not that easy.  Thought about it for a minute, and reversing polarity won't work.  That would give me a -5 to 0 range assuming I didn't short out the TCU.

What I realy need is the inverse of the resistance range of the TPS, which is what the renix TPS has (and it won't fit my throttle body).   I guess for now I could just leave the tps input to the TCU disconnected.  Need to dig out one of those old electronic books to figure this one out.

[Jesse-James]

Could you eliminate that connection by doing a manual controller? Cool toy.

AW Shifter