Shorted TPS and CLT fried my MegaSquirt?

[FORCED-INDUCTN]

Hello!

I've fried something but I'm not sure exactly what. I purchased a Nippon Denso 76 pin kit for my 1990 (NA6) MX-5 Miata per this guide's recommendation:

https://www.diyautotune.com/support/tec ... zda-miata/

I then assembled the ECU, following this guide and any tips/hints from the Miata guide:

https://www.diyautotune.com/support/tec ... -assembly/

I didn't have time/space to test and flash ECU until today. I pulled the coil-pack connector and plugged the MS into the factory wiring harness. When I turned the key I got a nice "sizzle" and some smoke come out of the MS case. I turned the key off right away and opened the case to investigate what I'd fried. I was expecting to see at least one blackened/burnt component but the "only" damage I can see are two burn makes on the PCBs, one on the adapter card and the other on the main board, the Micro Squirt daughter card looks fine. Here are the two images of the damage (damage is highlighted with red squares):

Adapter card:
http://twh.invadethenight.net/adapt.jpeg

Main board:
http://twh.invadethenight.net/main.jpeg

I inspected the board and noticed I had trimmed every single lead coming out of the bottom except for the TPS lead which was touching the CLT lead, oops!!! That's what get for checking everything over in a poorly lit room. I assume I'll have to replace something, or at worst the hole kit. I'm just curious if there is anything I can do to salvage what I have. I would also like to better understand what happened. Is it indeed likely that the shorted CLT and TPS pins fried the board?

Thanks in advance!

--Forced

[Matt Cramer]

Does this car have a real TPS, or just a throttle position switch? If it has the switch, make sure you haven't wired VREF to it.

[FORCED-INDUCTN]

Hey Matt, thanks for the quick reply!!

No this car (first gen Miata) does not have a variable TPS, it is the switch kind. I verified I did not jump VREF to pin 1N, my VREF and 1N pins are open. Here is a picture just as confirmation:

http://twh.invadethenight.net/wire.jpg

Forgive the flash, that is the only way I could get any clarity. Also I promise my soldering doesn't look so bad in normal lighting ;)

Are there any voltage test points I can use to verify the health of various portions of the board?

**EDIT**

I've done some more research and looked over my board as much as I can. I think I have a better idea of what might have happened. I foolishly neglected to remove the “ST SIG” fuel pump fuse per 1990-93 Miata DIYPNP guide I linked earlier. Forgetting to remove the "ST SIG" fuse seems to be a common mistake among Miata owners installing Megasquirts. I've found a few posts on other forums (ex: https://www.miataturbo.net/megasquirt-1 ... elp-84872/). Although this issue doesn't seem to critically damage the MS which is odd because mine seems to have burned a few traces. Tomorrow I will pull the "ST SIG" fuse and try to power up and flash the MS. Will post back with results!

Thanks!

--Forced

[prof315]

Not pulling the ST SIG fuse DOES cause enough damage to keep the car from starting in general. You'll certainly have blown the high side driver circuit that runs the fuel pump and quite possibly some other stuff.