MS Disconnected as soon as engine starts

[Blazer79]

I have Megasquirt 2 v3.0 mainboard
Firmware V2.90500
Bought assembled from DIYAutoTune
I also have the USB to Serial adapter bought from them.

Engine is a Chevy 350 TPI with a HEI distributor with module removed, just the VR signal going directly into MS, then into an Summit Racing MSD clone.

On Megastim everything works smoothly. I've had it running for hours with an AC adapter. Today I took the MS again for a test start. As soon as I crank the car appears to start then dies. Coincidentally MS disconnects from my laptop at that very same time. If I wait about 10-15sec before cranking again, Tunerstudio sometimes reconnects, other times I need to unplug the USB cable to the serial adapter and reconnect it. I'm running Ubuntu 14.04 and the USB adapter is recognized properly and works perfectly. I did try in Windows, and the result was the same, except windows sometimes gave a Blue Screen of Death when MS disconnected.

At first I thought I had a loose wire somewhere. I went through the wire harness carefully. All connections are welded. I have a common ground on my intake manifold. The only extra ground is from the firewall to the coil ground. I thought the MS itself was dead as long as I lost communications, but it isn't. If I crank again even while my laptop is disconnected, the car will restart, but die again. The most I've been able to keep the car running is maybe 2 seconds. But that's probably because I haven't been able to tune it. I have a clear cap on the HEI distributor (very cool and useful). When the car dies, I can see there's spark even after the engine dies and there's sometimes a little kickback on the crank.

Any help greatly appreciated.

[Blazer79]

Here's a 12 sec video of what happens when I crank it.

https://www.youtube.com/watch?v=9sscACCEwB4

Thanks again!

[trakkies]

I'd do a log of an attempted start. That should show any 'spikes' etc that are upsetting things.

[Matt Cramer]

Are you using non-resistor spark plugs by any chance? They put out enough noise to knock the communications offline.