94 TPS High Voltage
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Joined: Apr 2002
Posts: 93
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From: East Stroudsburg PA
94 TPS High Voltage
My idle was periodically increasing for no reason. The condition began to occur more often - then constantly.
I found that my TPS was reading about 1.2 volts with the throttle closed - I think it should be no greater than ~.8.
When I unmounted the TPS, the indicated position went to 0%. As a quick fix, I used a dremel to make the TPS "adjustable" - and I set it to .8 volts with the throttle closed.
After a 10 minute drive, the idle was high again. I had to stop working on the car and hit the road for work until next weekend.
BTW: I tried two TPS's.
Where to begin? Could it be my computer?
Thanks in advance.
I found that my TPS was reading about 1.2 volts with the throttle closed - I think it should be no greater than ~.8.
When I unmounted the TPS, the indicated position went to 0%. As a quick fix, I used a dremel to make the TPS "adjustable" - and I set it to .8 volts with the throttle closed.
After a 10 minute drive, the idle was high again. I had to stop working on the car and hit the road for work until next weekend.
BTW: I tried two TPS's.
Where to begin? Could it be my computer?
Thanks in advance.
Thread Starter
Advanced
Joined: Apr 2002
Posts: 93
Likes: 0
From: East Stroudsburg PA
Found the solution
I spent quite a bit of time doing continuity tests in the harness and veryifying grounds. I thought it was really strange that Datamaster would show about 3 volts from the TPS with it disconnected!
I went to the shop manual and started looking at the schematics. I noticed that the TPS sends a feed to a signal modulator for the ASR. When I took a look at the modulator, I realized it was full of water!
It's dried and siliconed. Best of all, my TPS voltage is fine now
I went to the shop manual and started looking at the schematics. I noticed that the TPS sends a feed to a signal modulator for the ASR. When I took a look at the modulator, I realized it was full of water!
It's dried and siliconed. Best of all, my TPS voltage is fine now
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The reason you see a high voltage with the TPS disconnected is that the ECM (or PCM in your case) ties the TPS input to a reference voltage through a "pullup resistor" (ALL inputs are either pulled up to a reference voltage or pulled down to ground -- this is necessary because of the way that analog inputs work -- if they are not connected to something they "float" and the reading is meaningless and tends to wander around). Normally the TPS will pull that reference voltage down to its normal reading, but with it disconnected it will go to the reference voltage. That's how the ECM knows that there is a problem in the circuit and this will usually set an error code.
Racer
Joined: Dec 2005
Posts: 421
Likes: 6
From: Keller Texas
There are three wires on a 94 TPS connector. Disconnect the pigtail and check for continuity. Sounds like there is break in the blue wire.
You could try to wiggle the connector at the TPS to see if a change in idle occurs.
If you have access to a Tech II you will need to reset the reference volt from the BCM.
You could try to wiggle the connector at the TPS to see if a change in idle occurs.
If you have access to a Tech II you will need to reset the reference volt from the BCM.
Cruising
Joined: Jul 2011
Posts: 13
Likes: 0
There are three wires on a 94 TPS connector. Disconnect the pigtail and check for continuity. Sounds like there is break in the blue wire.
You could try to wiggle the connector at the TPS to see if a change in idle occurs.
If you have access to a Tech II you will need to reset the reference volt from the BCM.
You could try to wiggle the connector at the TPS to see if a change in idle occurs.
If you have access to a Tech II you will need to reset the reference volt from the BCM.
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Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The later TPS sensors are not adjustable. The PCM reads it when you turn on the key and memorizes that number and calls it "idle". This is true for all years. That's why it's important to not touch the gas pedal when you first turn on the ignition.
You can read the various voltages on the TPS with it plugged in and the ignition on. Use a large safety pin and stick the point into the back of the connector (alongside the wire). You may have to wiggle it around to get it to go in fully and make contact with the connector pin. Clip/probe the safety pin with a voltmeter and read all three wires, referenced to ground. One should read zero (ground), one will be the reference voltage from the PCM and the center wire will be the TPS voltage that the PCM is reading.
You can read the various voltages on the TPS with it plugged in and the ignition on. Use a large safety pin and stick the point into the back of the connector (alongside the wire). You may have to wiggle it around to get it to go in fully and make contact with the connector pin. Clip/probe the safety pin with a voltmeter and read all three wires, referenced to ground. One should read zero (ground), one will be the reference voltage from the PCM and the center wire will be the TPS voltage that the PCM is reading.