Odd Fire TBI

[Willys43]

That's how I thought they worked for allowing the signal voltage, I just didn't realize that the remainder of the ref voltage went to ground. That was an excellent description. What confuses me is that the direction of current travel seems backward.
Is the W - or +?

[delcowizzid]

may i ask why 2 ecus as far as i know there is a buick oddfire hei type reluctor dizzy availiable that could run the gm 8 pin ignition module and one ecu

[1project2many]

What confuses me is that the direction of current travel seems backward.
Is the W - or +?

Well, now, that's a fine question. The ecm measures between W and GND so the voltage it sees will never be negative. But it could look negative if you measure between 12V and W. This measurement would show higher resistance if the wiper is at the +5V side of the pot, and it would show a full 12V when the wiper goes to ground.

why 2 ecus as far as i know there is a buick oddfire hei type reluctor dizzy availiable that could run the gm 8 pin ignition module and one ecu

oddfire engine has unequal pulse times between cylinders. ECM calculates rpm based on number of cylinders and time between reference pulses. Varying time between pulses would work out to rapidly increasing and decreasing RPM.

[Willys43]

"Look negative" wow that's loaded. I thought the ECM measured between W and the 5 volt ref? If the ECM measures between W And Ground, why the ref voltage.

Delco,
If you'll look at the Willys43 introduction thread, you will see how and why we ended up with 2 ECMs
Craig

[1project2many]

If the ECM measures between W And Ground, why the ref voltage.

Measuring between REF and GND gives a "known" or reference voltage. Second measurement between W and GND gives signal voltage. Then ECM can be programmed with max and min allowed values so if signal = REF or signal = GND a code is set.

[Willys43]

OK, then is the ref signal basically for comparison purposes to allow the ECM to calculate a corrected voltage for when then system voltage varies?

[dave w]

Best method to measure voltages / current / resistances, is with a test bench setup.

dave w

[lionelhutz]

I'll write about the TPS. The TPS is basically a potentiometer. The 5V reference is used so there is a constant fixed voltage for the sensor. That way, when the TPS is at 1/4 travel the output voltage is exactly 1.25V, when the TPS is at 1/2 travel the output is exactly 2.5V and when the TPS is at 3/4 travel the output is exactly 3.75V. Well, theoretically anyways.

It's be much harder to use these sensors if the reference voltage wasn't a fixed voltage. Say you tried to just use the battery voltage. Well, that can vary 1-2V and also contains all the switching noise and alternator ripple and other stuff such as that which means you have to constantly try to filter and correct for those variations. So, regulate it down to 5V and filter it so you have a nice steady voltage for the sensor and then you can just read the sensor output and know what it means without worrying about the reference voltage fluctuating. Same reason a dedicated negative wire is run from the sensor back to the ECM. It eliminates system noise and chassis ground connection issues. You'll see that the early systems used the exhaust system for the negative of the O2 sensor and then later systems used a dedicated wire and that change would have been for the same reason.