ECU Adjustment

[B Frye]

Okay ... I've searched through the archives to find anything related to this but didn't have any sucsess.

The idle mixture adjustment potentiometer on the ECU (76 2 L) has no effect regardless of how far it's turned CW or CCW.

The engine is is good shape. No vacumm leaks.

I find it hard to believe that the pot has somehow gone bad. Has the ECU got a problem; or am I missing something related to external sensors?

[bowlsby]

The ECU potentiometer only works at idle, or more exactly, when the idle contacts in the TPS are closed. When the TPS idle contacts open upon opening the throttle, the ECU enrichment circuits take over.

Are you sure your TPS is properly adjusted?

[pbanders]

Like Jeff said, the TPS needs to be adjusted properly so that the idle switch is on when the throttle is closed. If the pot has no effect, then it could be the pot is defective. I've got an ECU in my collection with a dead idle pot, it happens to be an 052, the one used on the '76's.

[B Frye]

Anyway to jumper the wires at the TPS to ensure the ECU is seeing an idle condition? I'm thinking this would verify the potentiometer is bad.

[Dave at Pelican Parts]

Yup, you can jumper those wires. I forget offhand which two they are, though...

--DD

[pbanders]

Originally posted by B Frye
Anyway to jumper the wires at the TPS to ensure the ECU is seeing an idle condition? I'm thinking this would verify the potentiometer is bad.

You could. Instead, I'd suggest testing your TPS with the throttle closed to see if the switch is on, and if not, adjusting it. Here's the tech article:

http://www.pelicanparts.com/techarticles/914_cooley/914_cooley_throttle_switch.htm

If you want to jumper it, it's pin 17 to ground (pin 12).