Megasquirt repair

[STOICH]

STOP.

The cap blowing may have done other damage, did you try the ECU on a stim first?

Before assuming the wiring harness has bad karma, troubleshoot something.
There are very few harness problems that can cause damage.
12v shorted to 5v is one of them, shorted to gnd or power sensor lines are largely the other scenario.

Its far more likely capacitor guts shorting something out in the ECU--tantalum caps go off like firecrackers, and almost all the bits are conductive metal fragments, explosion was contained in the ECU case, so was all the trash.

Completely agreed, and thank you for what I consider to be great advice. To answer your question: I plugged the ecu back on to the car with a 3amp test fuse which blew immediately after powering up the car. Going upstream however I have found the entire harness has issues. More info to add is probably justified. Not only the entire car, chassis, harness, fuel rail, the whole thing is garage built by myself and has been deep-desert "re-engineered" more times than I can count. If it were a factory harness I would be in much more agreement with you, but in this case, I'm blaming myself for a short in the chassis which probably used not only the ecu but other items as a fuse when things went south. To be to the point, nothing in the harness is working correctly compared to before this. I intend to bench test the ecu, but I very much intend to build an improved harness before it sees the trailer again. I did eyeball the board pretty closely, I did see a burn scar on the upper cover, but no other scorching was visible to my eye, not to say it isn't there. I have spent the last few nights looking at the harness itself instead of the Megasquirt manual, would anybody mind sharing with me the actual function of C16 please? I'll wind up in the manual anyhow I'm sure, but I'm focusing on the car at this point. {edit} I believe that the fuse that powers the ecu was actually blown by a relay that shares the same power downstream and probably not the ecu itself, I just tried the 3 amp to test my "mettle" and learned I had more to look for

[Piledriver]

C16 is the raw 12v input power filter.
It feeds everything, particularly the 5v regulator that runs the cpu and all the sensors.

My concern with the blown tantalum cap is the fine conductive crap is spews potentially shorting other things out--the scorch marks don't actually hurt anything, but the the metal guts certainly can.

If your other troubleshooting shows that the harness really is beyond repair, I suggest simply buying a new cable from diyautotune unless you make cables all the time.
That way all the wires are color coded and labeled every 12".

They'll even populate the spares for a few $ more.

[Clonebug]

I'll put in a vote for Mario's wiring.

You can get all the wires with the correct plug on the end and just order it extra long so you can fit it and then cut off the excess.

Every one of his wires are twisted pair or triple and sheathed with a nice expanding cover plus its heat shrinked on the plug end.

[STOICH]

I'll put in a vote for Mario's wiring.

You can get all the wires with the correct plug on the end and just order it extra long so you can fit it and then cut off the excess.

Every one of his wires are twisted pair or triple and sheathed with a nice expanding cover plus its heat shrinked on the plug end.

Looks like he does nice work! I have money for Mario- I have tried to get a hold of him a few times to no luck. I will say it is most likely due to my wiring not looking like that, that got me in to the mess in the first place.

[STOICH]

Thank you all for your help. I Have found my culprit, and am now back up and running.

[Clonebug]

Thank you all for your help. I Have found my culprit, and am now back up and running.

Well??? What was it???
Inquiring minds want to know......

[STOICH]

Thank you all for your help. I Have found my culprit, and am now back up and running.

Well??? What was it???
Inquiring minds want to know......

It looks like a well hidden yet melted zip tie allowed a well hidden throttle body wire to integrate the turbo into the wire harness. This throttle body wire would not have been there from the factory, as I was using it for powering Nitrous solenoids/TPS however I was not aware it was related to the same power source as the Megasquirt. (Guess I forgot) The Nitrous relay wiring had a bad connector and had allowed the power wire to fall right in between two cylinders on the manifold making it almost impossible to see. Stupid mistake, which unfortunately is what I was pretty sure I was looking for The help regarding C16 lead me down a different portion of the harness and is how I found it so the help really is appreciated. I think I would like to try to build a Megasquirt itself someday, I bought this one assembled so I'm pretty unfamiliar with its internal workings.

[Piledriver]

Cool, delighted shes running again.

MegaSquirt//msextra vs. complexity:
The actual electronics involved other than the cpu are almost embarrassingly simple, with essentially no input or output protection aside from fuses and a few zener diodes, its essentially ~as simple as it could have been designed and still work.

Working your way through the schematic with a local electronics wiz (they may be ~12 years old) should be possible.

The real magic is all in the firmware and tuning software.