alexisonfire07

I have gone through the procedure outlined on 4 crawlers website.
Here are my results: (multimeter set at 20k)
VTA - E2: .82
IDL - E2: no connection at any throttle position
VTA - E2 (WOT): 5.5
VCC -E2: 7.12

These are pretty close to spec, but my question is, with there being no connection at IDL and E2, does that mean I need a new TPS?

My truck is a 87 with a 22re. The symptoms my truck is having is o2 sensor code, switch signal code (11) and poor mpg. It'll stall when coasting to a red light and the idle wanders from time to time. Lots of things, I know and probably multiple causes for these issues but anyone with experience of bad TPS let me know what you think.

Thanks!

alexisonfire07

Another thing to not is that when going into "diagnostics mode" the idle doesn't change. Makes it hard to check timing correctly. I'm thinking this is related to the TPS issues above.

combatcarl

Did you try adjusting it to achieve continuity at closed throttle? If it's your first time playing with these, they can be rotated 10-15 degrees or so (heck, I don't know, just a guess) to get the IDL-E2 to close. Not implying you don't know what you're doing. And it's easiest to adjust it removed from the truck, unless you have gumby hands and a magical screwdriver, or have replaced the screws with allens.

alexisonfire07

Yes I just did that and achieved no connectivity. Obviously that's not good. Has anyone had this issue where the connectivity is gone on IDL and E2?

I remember reading somewhere that when these fail, they become open/infinite rather than no connection.

If I need to replace, should I go OEM?

Thanks guys!

alexisonfire07

Also, should the TPS snap back into place when WOT?

here's what mine does.

https://youtu.be/RnVpZXgvGcE

RJR

"open/infinite" and "no connectivity" are pretty much synonymous when talking about resistance measurements. The ECU needs a working idle switch to properly drop into idle mode, so that is likely to be one of your problems.

Regardless of what the FSM says, the better way to test the TPS (and VAFM) is to test it while connected in place on the vehicle. Turn the ignition "ON" (but don't start the engine), set your multimeter to VOLTS, and back-probe the VTA terminal. The voltage should sweep smoothly from ~0 to ~5 volts as you advance the accelerator from idle to full throttle. Any skips, jumps, or dropouts indicate a bad TPS, usually a dirty contact strip or wiper arm.

The reason this is a better method is that it exactly duplicates what the ECU is seeing. The ECU doesn't measure TPS resistance, nor does it particularly care about it. It measures voltage as the wiper moves across the potentiometer strip from bottom to top.

scope103

Yes. The one in the video is not working correctly. You could TRY cleaning it, but in general getting anything like water or paint thinner near the TPS is a no-no. But you don't have much to lose.

IF you have the A340H automatic transmission, and even better way (IMO) to test the TPS is to let the transmission do it for you. http://web.archive.org/web/201408160...48electron.pdf (page 191) This way, you're looking at how the ECU INTERPRETS the signal; you don't really care about resistance or voltage unless the ECU is getting the right answer.

Back probing is often necessary but still difficult because the connectors are sealed. And doing anything on the 3VZE TPS is difficult because of the angle of the connector.

alexisonfire07

UPDATE:
Thank you RJR. I was confused on what infinite meant when referring to resistance. Knowing what you told me now, I adjusted the TPS so that it is close within spec.
It now will go into "timing" mode when jumped.
New problem. Ridiculously jerky when in 1st and 2nd gear while applying throttle or releasing throttle. It feels like the ECU cuts fuel suddenly and then applies it suddenly.

My last truck did this so and I know it's TPS. Ordered the Allen screws from 4crawler but for now I'm going to play with the TPS using the old fashion screws.

Does anyone know which of the 4 wires in the TPS would have anything to do with causing this jerking motion?

alexisonfire07

UPDATE #2:
I was able to adjust the TPS so that I could jump the diagnostic/timing circut making idle change AND run normally without jerking and hesitating.

That video I posted was my TPS and my current theory is that the spring that returned the TPS center thingy wasn't working. I moved it around and it seems to return back normally now. It's probably a temporary fix.

I am going to drive it for a couple days and see how my ECU reacts to this new data it's getting. Would be awesome if my O2 senor code would go away.

Thank you all for your help! If I wasn't enlightened about ohm resistance, I would have been SOL!