Ignition control with MS2

[Tom_hd02]

Getting ready to do ignition control with MS2. Does anyone know how to identify the distributor's VR sensor polarity? Mega-squirt requires the VR (+) wire to be connected to pin 24, otherwise it will cause timing issues.

[dn010]

Assuming you're using the stock distributor and going by the wiring diagram, you'd use the wire going to the second to last pin of the Ignition ECU. This diagram was taken from the resource section and the wire is grayish, shown inside the screen cable:

EMCIgnition.jpg

[FABombjoy]

I mentioned this in a PM, but for posterity - once connected, disable the fuel pump & check timing on both 1 & 6.

The reluctor has 3 long, and 3 short teeth. If the VR wiring is backwards 50% of your engine may be timed incorrectly because the signal will be incorrect on the long teeth. BTDT.

[Tom_hd02]

After identifying the VR sensor polarity, I'm having issues with MS2 and ignition control. The engine runs very well with MS2 controlling fuel only. When I connect the distributor VR wires to the MS2 (so MS2 can control the coil), the engine runs ok but TunerStudio keeps losing sync every 20 or 30 seconds, and I had a hard time locking the timing. As an experiment, I connected the VR wires to a GM HEI 7-pin ignition module and connected the tach signal from the HEI module to the MS2, but I'm still having the same issue.
I see that diyautotune sells a VR conditioner module, but I want to hear from those of you that had issues with megasquirt and ignition control.

[dn010]

Did you try adjusting the pots to see if you can resolve the loss? (If not, see VR sensor section of your hardware manual for the procedure)

[FABombjoy]

Also a resistor was required for some PCB revisions, wasn't it? The surface-mount type 3.57? Although this seemed to affect higher RPMs more than anything.

But I agree, ensure the conditioner circuit is adjusted correctly.
If still an issue, use the sync error logger to capture an example and post it here for analysis.

[FABombjoy]

Also 20-30 seconds is a strangely long period. Could it correlate with AC compressor, fans, or something else switching on & off?

Something might be in the logs if you can post one.

[Tom_hd02]

I adjusted the conditioner pots on the MS2 (3.57 board). I also installed a 10k resistor inline with the VR + wire. No luck.
When I tried the HEI 7-pin ignition module, I connected the module in a similar fashion as the stock Bosch ignition module and ran the engine as fuel-only.
I will post a picture.

[Tom_hd02]

Hei7pinDiagram.jpg

I connected the R pin to the MS2 tach input, and ran the engine as fuel only. I left the "B" and "E" pins disconnected. "B" is the bypass pin, which allows MS2 to control timing when 5 volts are applied to the B pin. "E" pin is the dwell and timing signal coming from the MS2 (which I left disconnected for now).
hei.jpg

[FABombjoy]

Speaking from direct experience it may not be related to the VR input at all.

A data log and a high speed sync error log would be the preferred place to start, so that the sync loss can be characterized.