Got a 99 GT with a aftermarket plenum and a bbk 75mm TB. i messed with the throttle stop screw to get the bind out when i first installed it. the TPS that came with the TB went bad, so i contacted bbk to make sure stock TPS would work for a replacement. Of corse it did, but ever seince i've had odd issues with throttle smoothness, fuel mileage, and (from how it smells) improper fuel delivery (rich and lean) before and at WOT. I got the volt meter out and started checkin stuff and here's what i got; Closed: Ref= 4.2 volts Sig=4.2 volts. As i open it: Sig drops down to .20 volts instead of goin up. So my question is, is it the TPS bad or PCM messed up. I don't usually get stuck, but im highly confused and could use some guidance. Thanks in advance!
TPS problem.....really confused
- Thread starter Frankenstang838
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trinity_gt
10 Year Member
Wierd. Are you measuring this relative to, say, the battery -ve terminal (e.g. the cylinder head as a ground)?
It sounds like the V+ and GND wiring is backwards on the plug leading to the sensor. Has the wiring ever been touched?
It sounds like the V+ and GND wiring is backwards on the plug leading to the sensor. Has the wiring ever been touched?
I screwed up. They changed the wire colors from 96 to 99 and i was measuring everything backwards. I went and looked at my schematics rite after i posted this and seen the wire color differences to the TPS. I had to slightly modify the TPS (i found my spare so i didn't mind) to make it adjustable. its sitting right at .52V at idle, but when i kick the throttle all the way open, my TPS only reads 4.60V instead of the around 5V its supposed to. I played around with it and could get the WOT up to about 4.8V, but when i did that, it put my closed volts at 1.2 which is too high. So i put it back to where i had it first and i got smoother accel, and no rich or lean smell at WOT. A buddy told me that the 4.6L cars were non adjustable cause the EEC 5 can take up the slack that the EEC 4 can't. Any truth to that? And is my computer reading WOT even tho my TPS volts at WOT is 4.6?
trinity_gt
10 Year Member
4.6V at WOT is fine. The computer will learn parameters such as closed/idle and WOT voltages over time.
wmburns
SN Certified Technician
The 96+ model years LEARN a new TPS closed throttle value at engine start time. The absolute value of the TPS doesn't matter.
What DOES matter is that each time the throttle closes, the TPS produces the SAME value. If not, the PCM will not know when the throttle is closed and a high idle is the usual result.
If working the throttle open and closed does not produce the same TPS value, the very first thing should be to check the setting of the idle set screw. This is important! Has it been set according to the manf recommendations?
Next look first for any loose or binding in the throttle linkage. Clean the electrical connector to the TPS.
If still a problem, the TPS may be bad.
Any value over 4 volts will let the PCM know the throttle is at WOT. Again the absolute value is not all that important.
What DOES matter is that each time the throttle closes, the TPS produces the SAME value. If not, the PCM will not know when the throttle is closed and a high idle is the usual result.
If working the throttle open and closed does not produce the same TPS value, the very first thing should be to check the setting of the idle set screw. This is important! Has it been set according to the manf recommendations?
Next look first for any loose or binding in the throttle linkage. Clean the electrical connector to the TPS.
If still a problem, the TPS may be bad.
Any value over 4 volts will let the PCM know the throttle is at WOT. Again the absolute value is not all that important.
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