TPS Voltage Adjustment
By Dan Thompson
[Editorial note: Zak Nilsson wrote that he had a problem with the reading, it was negative. Switching the leads on A and B fixed his problem. We're taking the liberty to reverse the '+' and '-' so that you won't have his problem.]
Imagine that this picture is what the back of your TPS wiring harness looks like as it's plugged into the TPS:
----- | A | -------- | B | | -------- | C | -----
What you need to do is get a DVM and hook the positive lead through the back of the harness into "B" and hook the negative lead through the back of the harness into "A". It's easiest if you straighten a couple of paper clips (I used my wife's sewing needles...she nearly killed me) and shove them into the openings and hook onto 'em with alligator clips, but *DON'T* let them touch. Turn the ignition on (don't start the car) and check the voltage between "A" (-) and "B" (+). It should be between 0.45 and 0.55V. If it's not, you'll need to loosen (but not remove) the two screws or bolts that hold the TPS to the throttle body. Rotate the TPS until you get the proper voltage and tighten the screws, making sure it doesn't go out of adjustment when you tighten it down. As a final check, open the throttle all of the way. You should read around 4V. If so, great! If not, uh...my condolences.
Ford guys adjust the TPS to "fool" the computer into thinking the throttle is opened farther than it actually is. It supposedly works, but it never made much sense to me. It seems that the ECU would think that WOT is achieved at a certain voltage (like 4V on ours) and going farther than that doesn't do any good. It would also seem that if the TPS is "turned up" too high, the ECU would never see the correct voltage for closed throttle (like ~0.5V on ours) and the idle would be all screwy. But they claim it works and claim to have back-to-back 1/4 mi runs to back it up. It sounds like a good question for Jim or Clark at JWT.