PSA: Megasquirt and Ford EDIS

[nbuscemi]

As a professional auto tech and ACVW enthusiast I’ve seen a lot strange things. Today I saw something new and I wanted to share with the group.

Back story:
1968 Type 1 sedan, 1600cc turbo with a home brewed EFI system built around a Megasquirt 2 ECU and Ford EDIS. The car seemed to lack power off boost and misfired at the upper RPM while on boost. On top of that, the car liked to stall when coming to a stop. After weeks of trial, error, and fruitless troubleshooting, yesterday I decided to verify the Ignition Timing with a strobe light. The timing was fixed at 20* of advance. No matter what I did in Tunerstudio the timing would not change. Not even increasing RPM would cause the timing to advance.

Since EDIS is able to run the coils without PCM input, I figured there was an issue with either the PIP or SAW signal. Using a DSO (these things are worth every penny!!!) I verified that the PIP was strong and making it to the MS2. The SAW on the other hand was stuck at 0V.

My first (and incorrect) assumption was that there was an issue with the PCM. Turned out that if I disconnected pin 36 of the DB37 connector that SAW signal would start.

Turns out I have a short to ground in my SAW circuit. What makes things interesting is the fact that it was the wire shielding that was causing the short. Once I disconnected the shielding ground, the short went away. For what its worth, I reused this wire from the donor Ford harness. I shouldn't be surprised that a 25 year old wire would cause a problem.

After running a new wire from MS2 to the EDIS module I finally had control of my ignition timing.

Now some of you EDIS gurus may have noticed that the fixed timing was 20* instead of the 10* that Ford specifies. I’ve temporarily corrected this with the Crank angle offset adjustment in Tunerstudio. I will eventually readjust the CKP to permanently fix.

Hope this helps someone in the future…

[panel]

Thanks for documenting this !

[nbuscemi]

Update:

Along with previous repairs mentioned above, I also modified my CKP sensor bracket to allow 10* +/- of adjustment. I know Tunerstudio allows for sensor offset adjustment but I wanted to see the 10* BTDC from the EDIS module without the SAW signal (much like pulling the SPOUT connector on the OEM Ford setup). Now my spark table matches the strobe light with a 0* offset in TS.

-Nick-