Throttle position sensor

[Kyzrsoze]

I'm working on an old 1994 Silverado with OBD1. 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?

 

[8675309]

some tps sensors are adjustable. are you holding the butterfly
valve wide open by hand or by pedal? cable could be stretched

 

[Greybeard]

Looking at the pix I don't think the engine should be running. Turn key on and check. It could just be feedback from the computer or tps. Check idle to full open, if not reached full voltage on wot adjust cable, they do stretch or something under pedal.

 

[Kyzrsoze]

Looking at the pix I don't think the engine should be running. Turn key on and check. It could just be feedback from the computer or tps. Check idle to full open, if not reached full voltage on wot adjust cable, they do stretch or something under pedal.

Good thought. I am actually testing it power on, engine off. I tried it first by working the the throttle by hand and rotating it to full stop (wot).
I then tried removing the sensor from the throttle body and rotating the sensor mechanism to full stop (wot). I'm getting the same result at around 2.5 volts.

 

[Kyzrsoze]

some tps sensors are adjustable. are you holding the butterfly
valve wide open by hand or by pedal? cable could be stretched

Good thought. I don't know if this one is adjustable, but the travel matches the travel of the throttle. Yep, I am moving the butterfly by hand.

 

[8675309]

Good thought. I don't know if this one is adjustable, but the travel matches the travel of the throttle. Yep, I am moving the butterfly by hand.

if it looks like the one pictured with oblong holes it is adjustable
some were some werent and you can buy universal fit ones that are
ac delco or better

besides that the only other thing i can think of is when checking
voltage you may want to back probe the ground at the pigtail

it wouldnt hurt to clean up the ground cables

thats a nice truck you got btw

 

[Greybeard]

I am pretty sure (not positive) that you should have 5 volts at wot. I would start checking the grounds and like suggested clean them up a little and see if that helps.

On the other side, I have changed out 5 fuel pump relays until I received a good one. Also 3 o2 sensors until a good one was found. I know it's cost more but if all else fails try a OEM tps. Computers are funny when you start talking micro voltage.

 

[Kyzrsoze]

if it looks like the one pictured with oblong holes it is adjustable
some were some werent and you can buy universal fit ones that are
ac delco or better

besides that the only other thing i can think of is when checking
voltage you may want to back probe the ground at the pigtail

it wouldnt hurt to clean up the ground cables

View attachment 1311089
thats a nice truck you got btw

I was trying to figure out how it would be adjustable, and seeing the pic it makes sense. Mine isnt, but it's full range of motion matches the the throttle body, and if I test t by moving the TPS manually I get the same result.

I'd have to say that the truck is more original than nice, but I'm working on it.
I love the simplicity of it compared to newer stuff.

 

[Kyzrsoze]

I am pretty sure (not positive) that you should have 5 volts at wot. I would start checking the grounds and like suggested clean them up a little and see if that helps.

On the other side, I have changed out 5 fuel pump relays until I received a good one. Also 3 o2 sensors until a good one was found. I know it's cost more but if all else fails try a OEM tps. Computers are funny when you start talking micro voltage.

It should definitely be 5 volts and the reference signal from the PCM is 5 volts. It's not giving me CEL. I agree on parts quality, and I hate the possibility that I may need to go through several to get it right.

 

[Greybeard]

Just a thought, when you replace it I know it won't line up perfectly, you need to rotate it sometimes up to 20/25 degrees. If that happens you would read low. Try removing it and install the opposite direction (up vs down or down vs up) to rotate it into place. I had that problem with different rvdt that wouldn't calibrate.