Quote:
Originally Posted by caffeineaholic
FYI: 1985 Caprice - 305 -- Q-jet E4ME (original) -- TPS sensor less than 1yr old and properly installed/seated
Hi all,
Yesterday I adjusted my TPS to the specified voltage at curb idle (.48V). It was off by about .30 volts and the factory manual says to correct it if it is off by +/- .05V... I did this and followed everything very carefully and used threadlocker to keep the TPS adjustment screw from moving per the instructions.
The issue is that the voltage reading will NOT stay the same. The throttle will stay at curb idle and the TPS voltage reading will go from .48 volts slowly down to .42 and eventually (several mins) .38 volts.
Even when I correct it back to .48 volts it does this again, and again...
I tried this with the engine off (IGN on) and also with the engine on-- same result either way. This removed the variable of vibration affecting the TPS reading while simultaneously adding the possibility of the battery slowly (slightly) draining and thereby affecting the 5V signal/source.
Based on the time it takes for it to go down to about .42 volts I do not think the battery slowly discharging could be the cause.
The only other variable I can fathom is heat but I don't see why this would change the voltage readout from the TPS...
Also, I'm positive that the adjustment screw is not loosening/tightening from vibration because it is difficult to move with the adjustment tool (whereas before it was very easy). The choke was fully open (full operating temp) and the idle speed solenoid disabled during all testing in order to be sure that the throttle position would not change at all.
Finally, I just thought it was worth mentioning that in another section of the FSM it says that the TPS voltage reading can vary by +/- .10 volts
Sorry for the long post, thanks for your time.
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I would say this is because the TPS is defective. what can cause this is carb cleaner. this corrodes the electrical parts. as mentioned this component has had many failures. carb cleaner is usually the cause.
as the resistor [tps] gets hotter the resistance increases this means a lower voltage. most likely 5 volts is locked at 5volts.
with all power voltage /connector removed move the tps and measure the resistance . use a non digital meter is best see if the movement causes a loss of continuity.[open circuit]
5.oL engine it should be .5volts....