TPS junk? Carb guys can ignore this!

[zachmac]

I wasn't sure if this should go in electrical or engine so I posted it here.

I am cleaning / refurbishing my FI system on my 1980 Spider. I THOUGHT I had a decent running car but if you look at my earlier post on the injectors, I hve already found out one was basically an open leak constantly dumping fuel in one cylinder. Now I also suspect I have failed TPS switch.

If I understand correctly the TPS is basically a variable resistor (potentiometer) that takes a 5v signal from the ECU and depending on position sends somewhere between full voltage to very low voltage back to the ECU to indicate throttle position. I think it should be 0 ohms at closed throttle (sending 5 volts back) and minimal volts (high resistance) at WOT. This tells the ECU to lengthen the pulses as you open the trhottle and shorten them / shut off the injectors at closed throttle, correct?

The one off of my "running well" car is basically an open so it hasn't been passing any signal back. I believe this means the ECU has been sending maximum duration pulses to all of my injectors all of the time. Seems like maybe I was running a bit rich?

BEFORE I order a new TPS, can anyone confirm what I have stated here and that an infinite ohm reading between TPS pins 18 and 2 regardless of TPS position does indeed indicate that is is now a paperweight?

BTW, yes I have Bradleys excellent write up on the system, I just want to make sure I am understanding it correctly.

[Snoopy]

The Spider TPS is only a switch no two switches:
One switch idle position and one switch full throttle...

[zachmac]

Based on this I should see open between 3 and 18 and shorted between 2 and 18 at one extreme of travel and the opposite at the other extreme of travel. Correct. So, if I only see infinite resitance between 2 and 18 regardless of the position I still have a bad switch.

[zachmac]

Snoopy,

Thank you for saving me some $s. After further testing my switch does indeed work exactly as the diagram you provided shows.