TPS Adjustment
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Junior Member
Joined: Nov 1999
Posts: 67
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From: Newmarket, ON
Car: 1986 Z28
Engine: 305
Transmission: 700r4
Axle/Gears: 3.23
TPS Adjustment
When making adjustments to the TPS should I get a voltage reading with the ignition in the on position or should the engine be running?
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Joined: Jun 2001
Posts: 215
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From: Oklahoma City, OK. USA
It needs to be done with the engine off -ignition on. That is unless you don't mind reving your engine up to 5500 RPM in drive to see what the mid range & WOT volts are. 
[This message has been edited by whiteroc (edited July 06, 2001).]
[This message has been edited by whiteroc (edited July 06, 2001).]
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Joined: Jul 1999
Posts: 10,907
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From: The Bone Yard
Car: Death Mobile
Engine: 666 c.i.
I HOPE you are not trying to adjust your TPS under the false impression that you will get "more WOT" due to higher voltage. I REALLY would like to see this myth killed.
The TPS is NOT where you make these adjustments. Its in the eprom, plain and simple. The eprom sets the level that PE (the real name for WOT) kicks in. It does it anywhere from 50% - 70% TPS, depending on your RPMS. Even at 70% TPS (4800 rpm btw), this is WAY under 4.00 volts.
The only thing to concern yourself with the TPS is the minimum voltage setting .54 - .65 volts. If its is there...fine...leave it alone and forget the mechanical "Flathead Ford" tricks from the 80s when no one knew how to get inside an eprom. You can cause more problems than a "perceived problem" (not going into PE)... which seldom exists.
What is more of a concern is the amount of extra fuel and spark advance you get when you enter PE. Adjusting the TPS does NOTHING to overcome the real problem...needing more fuel and spark. Again, the eprom is your correct answer.
The TPS is NOT where you make these adjustments. Its in the eprom, plain and simple. The eprom sets the level that PE (the real name for WOT) kicks in. It does it anywhere from 50% - 70% TPS, depending on your RPMS. Even at 70% TPS (4800 rpm btw), this is WAY under 4.00 volts.
The only thing to concern yourself with the TPS is the minimum voltage setting .54 - .65 volts. If its is there...fine...leave it alone and forget the mechanical "Flathead Ford" tricks from the 80s when no one knew how to get inside an eprom. You can cause more problems than a "perceived problem" (not going into PE)... which seldom exists.
What is more of a concern is the amount of extra fuel and spark advance you get when you enter PE. Adjusting the TPS does NOTHING to overcome the real problem...needing more fuel and spark. Again, the eprom is your correct answer.
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You should check the WOT voltage too, and make sure it is in fact more than 4 volts. On both factory chips (86 and 88) I have, the PE is set at 80% not 50-70. I took it upon myself to assume the max was 5V and 80% of that is 4V. I have verified this with 2 different scanners that below 4V the cars were not going into PE mode with the voltage at WOT below 4 volts.
To check it, you want the engine OFF, key on. I use a needle and stick it into... I think its the blue wire, and the other end to ground. Check the idle voltage, WOT, and make sure inbetween the TPS voltage doesnt jump around it should be smooth and increasing as you open the throttle. Also make sure when the pedal is fully depressed in the car that the throttle is actually open all the way.
To check it, you want the engine OFF, key on. I use a needle and stick it into... I think its the blue wire, and the other end to ground. Check the idle voltage, WOT, and make sure inbetween the TPS voltage doesnt jump around it should be smooth and increasing as you open the throttle. Also make sure when the pedal is fully depressed in the car that the throttle is actually open all the way.
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