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Old 04-22-2021, 12:15 AM   #29
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Join Date: Aug 2014
Location: Boulder CO

Originally Posted by Fa182 View Post
Just came here to say I have no idea what you guys are talking about, but it's awesome seeing what you are doing.
Thanks, just call us "geeks at play" ;)

If you're interested, here's the high level view. The LH Jetronic system splits the engine control between the EZK box (ignition) and the ECU box (fueling). The EZK box monitors the engine rotation, using the CPS sensor, and controls when to trigger the spark. The ECU box monitors the incoming airflow, using the MAF sensor, and controls the injectors to provide correct fueling.

For better engine control, the EZK and ECU boxes communicate with each other. The EZK box sends the current RPM, and knock detection, to the ECU. In the other direction, the ECU sends the current engine load to the EZK. If you're familiar with old school distributors, the engine load is the electronic version of the vacuum advance can. At light load (higher vacuum), timing needs to be advanced for best power. This thread is about the [painfully] exact details of how the ECU determines the engine load, and communicates that information to the EZK using the Tq load wire.


... now back to our regularly scheduled topic...

I was going to post some Tq measurements from a '954 ECU, but my buggy Hantek scope crashed Windows 10 before I saved. #*!%@! piece of junk. I'll redo the measurements and post them tomorrow.

The ATmega processors include "pin change interrupts" that trigger when any out of a group of pins changes. This allows more than the simple arduino INT1 INT2 processing. The interrupt routine needs to keep track of the previous pin states and compare them to the current pin states to determine which pin, or pins, changed and triggered the interrupt. There's a good, but long, description of this here:

I forget what I'm using on the benchtop setup, but I think some of the measurements are using the pin change interrupt.
D - Your plots are interesting, and show that Tq behaves a bit differently on a real car, instead of my steady-state benchtop measurements. Once the real monitor/logger are running, this should be easy to investigate.
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