This is topic WTF with TPS? in forum Tech Talk at Northern California Ford Owners  .


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Posted by BCINGUU (Member # 2397) on :
 
Any sensor / PCM gurus out there?

I tracked down a problem with my TPS that was causing numerous idle, economy, and drivability problems. The TPS voltage was essentially not changing at all during driving. I replaced the TPS sensor but that did not help.

Turns out the reference and sensor return voltages were both 5V. On the wiring diagram, the TPS, EVP, and MAP sensors all have the same reference voltage connection (5V) and all sensors on the car have the same return wire (should be 0V).

Both the reference and return wires end up back at the ECU (pins 47 and 24 or something like that).

Just to see what would happen, I grounded the return wire. Probably not supposed to do that but what the hey. By doing so, I brought the return voltage down to 0 like it's supposed to be and the TPS started working correctly. Now the TPS output is between .94 and 4.5 or so volts and the car is running much better. So I left it grounded and drove it in to work today.

However, this is a band aid. What's really wrong with my car?
 
Posted by BCINGUU (Member # 2397) on :
 
Oh no! Double post!

[ July 19, 2005, 03:55 PM: Message edited by: BCINGUU ]
 
Posted by BCINGUU (Member # 2397) on :
 
Any help? I can't believe I have you all stumped! ;-)
 
Posted by 92coupe (Member # 1957) on :
 
i can have a better answer for you later on but off the top of my head:

sounds like your pcm has a bad ground and/or those 2 pins broke loss and dont have a connection to ground.

if you have a friend that upgraded there pcm try out the stock 1 to see if it works correctly.

and grounding those 2 seperately is not "bad" the manufacturer puts most sensors ground through the pcm so they all share a common ground. also to protect against bad grounds. hope a helped a little.

Justin
 
Posted by BCINGUU (Member # 2397) on :
 
Thanks for the reply, that does validate my action and I feel a little less guilty about it! ;-) The car is running great now and I have'nt had a problem since I did this.
 
Posted by Cobra5.0Jeep (Member # 1482) on :
 
how did you check the volts on the TPS? and how was the car running that you knew something was wrong with it?
 
Posted by BCINGUU (Member # 2397) on :
 
Measured TPS between black and green wires off the TPS. You can jam a test lead into the back of the harness connector from a DVM.

Some of my Symptoms:

1. Idle would drop below set point upon release of accelerator - driving down the road, come to a light, let off the gas, car almost stalls.
2. Rough idle and hunting
3. Could not adjust idle screw to let idle go below 800 without the car dying
4. EEC was using the altitude spark table, not the sealevel one
5. Major hesitation on Heavy acceleration
 




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