MSefi.com read only forum (Jan.15,2018)

IMHO, not a good idea to simply swap components at random.

Thanks trakkies. That's the conclusion I came to and not having the electronics knowledge or proper tools, I decided that it was best to just have a pro fix it so I sent it in yesterday.

Well, gave up trying to fix it myself. Thanks to everyone that had ideas - really appreciate the support of the community.

Sometimes you just have to bite the bullet and turn it over to the pros.

I'll post the diagnosis when it gets back.

More data -

I just switched the jumpers on the board to go VR rather than coil negative terminal for tech input. This should, as I understand it, use a completely different set of components to handle the tach input circuit.

If the problem goes away, it's pretty conclusive that it's in the opto ...

R12 checks out at 390 ohm

Would it be worth it at this point to just replace the opto input chip U3 to rule that out? Any other components as part of that circuit that should also be swapped out?

Thanks

Thanks for the suggestions, downwardspiral.

Here are the results:

Battery voltage was found on S12, S12C, D3, U5 and D9. (Q9 and Q12 were not installed since I'm using high impedance injectors)

5 volts was found on S5, 5v proto holes, D9, U5, D19 and CPU 1,20,31.

D19 is cold

So it doesn't ...

Here is a quick follow-up video to show the problem I'm experiencing with my Megasquirt. It's easier to show than to explain.

Any suggestions on what to check?

I've been working through the details on my Megasquirt installation (MS-II, ver 3 board) on an air-cooled VW engine. On background, the conversion is using Mexican intake with a Ford Escort throttle body, GM sensors, coil negative post for tach input. Megasquirt build went well and everything tested ...