Grounding of TPS sensor

[Shaun41178(2)]

Maybe someone here has an answer to this. I have tried several tps sensors with my new intake setup, and both have thrown codes. I have verified according to the service manual, that my wiring is good. Grounds are good, and I am getting voltage. I have verified that my tps sensors are good by using my VOM. My safc has a TPS output reading on it, and it goes from 0% at closed throttle to about 94% at WOT with no dead spots.

However when I hook up the sensor it keeps throwing a code. It does not go away when revving it or bringing the rpms steady up over 2k rpm. My sensor looks just like this one. Obviously I had to modify my wiring harness connector but all the colors matched, and if I swap colors, I have no TPS readout, which leads me to believe I have the wiring hookups correct .



You will notice that metal plate inside the sensor. Does that metal plate actually ground on the throttle body housing? I have looked at pics of other sensors, and many are fully encased in plastic, leading me to believe that the sensor grounds only with the wiring harness. Is this one different and uses the little metal plate to ground on the tb as well?

I am guessing my bad tps is causing my motor to run stupid rich. Code 22 is what I am tripping.

[jelly2m81]

If your sure your wiring is correct then an easy way to test your theory of grounding of the sensor is to simply cut out a paper or light cardboard backing to cover the metal area of your TPS and see what happens.

[The Dark Side of Will]

Download the service manual from www.fieronews.net and look up the trouble shooting tree for Code 22 (page 6E3-A-34)

Code 22 sets when:
-Engine is running AND
-TPS signal voltage is less than .2 V for 2 seconds.

If your sensors are good, you have a wiring problem.

[fieroguru]

The TPS and Coolant Sensor share the same ground wire going to the ECM.
Lack of coolant sensor input causes a pig rich condition.

[Shaun41178(2)]

Yes it is a rich condition. And Will, yes I am using the 88 service manual. Not sure if that page you referenced is correct, but it sounds about right. I am following the flow chart and each time it tells me its the sensor. But I have gone through two sensors. Could they both be bad? I suppose. However I have hooked up my old sensor from a factory v6 tb, and I am still throwing a code for that sensor as well. So tech its 3 sensors since the flow chart says my wiring is good, and that my ecm is seeing what it is supposed to.

[The Dark Side of Will]

I am following the flow chart and each time it tells me its the sensor.

Sorry... I flaked on the sentence in your original post saying you'd verified according to the manual.

I don't have the manual in front of me and am going off the cuff... if you've already done some of these things, then don't bother doing again.

-The conditions for setting the code are what I mentioned above... I'd back probe the ECM pins to measure TPS voltage (key on, engine off) with a DVM to verify that the ECM is reading them correctly.
-Also back probe the 5V wire relative to the battery negative terminal to make sure that it's actually getting 5V.
-Finally, disconnect the negative battery terminal and measure resistance between the negative battery terminal and the ground pin at the TPS sensor.

Basically, the TPS is just a potentiometer used as a variable voltage divider. If it's working correctly, has a 5V supply and a low resistance ground, it should give good voltage.

If the ECM reads the closed throttle voltage as too low, there could be one of three things wrong:

-Mechanical adjustment of the sensor is incorrect. I'm not sure if your TB has a mechanical TPS adjustment... The photo of the sensor your posted doesn't have provision for adjustment.
-The TPS signal wire is grounded somewhere (chaffed insulation, etc.)
-The ECM is not correctly reading the voltage (need new ECM at that point)

[Shaun41178(2)]

Ok got it. Decided to stop being a fiero owner and buy a new tps. it purrs good now with no codes.

[The Dark Side of Will]

Haha... good to hear.

You threw those others away, right?

[crzyone]

Ok got it. Decided to stop being a fiero owner and buy a new tps. it purrs good now with no codes.

[AkursedX]

Ok got it. Decided to stop being a fiero owner and buy a new tps. it purrs good now with no codes.

Haha, good work!

[Shaun41178(2)]

Haha... good to hear.

You threw those others away, right?

Not yet, you want them? $25 each

Its funny to think I had 3 bad tps sensors. Oh and fyi, that little metal plate in the tps sensor isn't grounded to anything. I took a bad one apart, and it basically just acts as a dust shield.

[The Dark Side of Will]

Were they old junk on the shelf that had been hanging around a few years?

[Shaun41178(2)]

one I picked up on ebay used, one was from a 3400 tb I had from an intake I bought, and the third was from my old original fiero v6 throttle body that I had on my old turbo setup with iron heads which was working when I removed it.