TPS

[V_Kint]

I'm working on an old 1994 Silverado 5.7 TBI. I had an check engine light (code 21) that pointed to a bad TPS. Supposedly a good TPS should show less than .74 volts at idle (no pedal) and gradually rise to 5 volts at full throttle. I've now installed two different replacement parts that show good at idle and only 2.5 volts at full throttle. Am I measuring something wrong or missing something?

 

[skylark]

Are you getting a correct 5-volt reference from the computer?

 

[skylark]

I don't remember the pin out off the top of my head but one of the wires is the 5-volt reference from the computer. The other two are a ground and the one that sends voltage back to the computer to determine throttle position. If your ground is crud or your 5 volt reference is screwed up then you will get a bad signal back to the computer.

 

[98 Nitro]

What TPS did you buy? The cheap house brands do not work correctly.

 

[V_Kint]

Are you getting a correct 5-volt reference from the computer?

What TPS did you buy? The cheap house brands do not work correctly.

I am getting a good 5v reference signal. At idle the TPS signal is where it should be. Working the throttle linkage the return signal climbs smoothly up to 2.5v at full throttle, exactly half of what it should be. I'm not getting a CEL. It was a cheap brand from a local parts store, so that might be the issue. I guess I need to pick up an OEM unit for comparison.