"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
Last edited by Willys43; 03-10-2016 at 03:15 AM. Reason: bad grammer
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.If the ECM measures between W And Ground, why the ref voltage.
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?
Best method to measure voltages / current / resistances, is with a test bench setup.
dave w
I agree Dave, test bench is built and wired, I just have to double check the wiring, and get it hooked up to a computer and I off and running. Actually it will probably be off and crashing at first, but I'll get thru it. Even wilth a test bench understanding what your seeing can be pretty confusing at times.
You did a write up on VE tables, how will I have to adjust mine, going from a 4.3 6 Cyl to a 3.2 dual ECM 6 Cyl? Set each ECM for a 1.6 3 Cyl ?
Last edited by Willys43; 03-11-2016 at 03:00 AM.
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.
Craig, Anything new with your project? Hope things are moving forward.
Hi Eds,
Things are still moving forward, I'm working on the test bench with dual computers, I've eliminated a few bugs, burned a couple of chips, and now I'm working on data logging so I can check to see if the ECMs are getting the same, correct signals from the sensors. This stuff is all new to me so it takes awhile to figure it out.
Craig
It looks like everything is working right. TPS,MAP,ETC signals look good. Both computers are outputting spark signals and injector signals. I'm unable to tell if the spark and injector signals are staggered from even to odd cylinders because they're too close together. The RPMs look right. I am able to create and flag errors by manually varying input signals. Fuel pump relay works properly. Computer seems to be adjusting the timing. Guess maybe it's time to start setting up the harness I'm gonna use.
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