DIYPNP causes extreme rich condition
 

Hey guys
I have a 95 base with the 94 motor from my last miata currently in it.

The 94 car was running successfully on the DIYPNP (batch injection) earlier this year. I wrecked that car. Right before I was going to pull the motor I plugged in the DIYPNP once again to test something and it was hard to start and sounded 'subaru-ish'. Wideband was pegged full rich and there was literally raw fuel shooting out of the exhaust. I tried reverting to an old tune, leaning out the map map. recalibrating all sensors, req fuel, etc to no avail.

Strange part was when i plugged the stock ECU back in it was only marginally better. The car still wouldn't run leaner than 10:1. I decided to pull the motor to prevent damage and see if it would be alright once i swapped it into my other miata.

It has been running great on stock ECU for a few months. Finally went to try the MS tonight and the same rich condition returned. This time when i went back to test it on the stock ECU it started of extremely rich but returned to normal after about a minute (presumably just burning off all the extra from running with the MS) unlike the last time this happened.

Been looking over the board and just noticed this. Are these drivers on the microsquirt board replaceable?

Forgive me for no datalog but I can post one at request. scared of washing the walls and ruining ring seal by running it anymore is all. Should've logged it before :vash:


https://cimg6.ibsrv.net/gimg/www.mia...b32c6e3826.jpg

Should just be a transistor/mosfet. Google the number printed on it. If you're careful you can swap it with a good pair of tweezers and a heat gun.

slick. Will try and swap it out tonight! Believe I have an extra from the sequential injection circuit parts i never used.

Attempted to remove the transistor and I managed this :)https://cimg1.ibsrv.net/gimg/www.mia...54cd1820a7.jpg

Is it feasible to try and mount a replacement transistor elsewhere and run (small) wires from it to the board where needed? Is this board full on KO'd?

Also is there a way to test these VND transistors with a DVOM? Not sure the condition of the spares i have/

Meh, looks fixable. If you're not comfortable with SMD soldering, find a buddy who is. That should be feasible with good soldering iron. I fixed something similar on my RusEFI.

Yeah that's not being careful. You snapped the leg clean off. Were you using a heat gun?

A soldering iron has no place in SMD soldering. You can't properly heat all 3 points. Carefully apply heat with heatgun until solder is liquid. Lift off the board. If there is any resistance at all the solder hasn't melted yet.

the trace started coming off, it's okay.

you need to heat up the rear tab now and release it from the copper trace.



@spartan, these FETs are still child's play for a soldering iron.

Certainly doable with a soldering iron, but an infinity times easier with a heat gun. OP pulled a trace up and ripped a leg off the old one. Me thinks using a soldering iron to install the new one without overheating to the point of damage may be a struggle.


To OP, there isn't an easy test for transistors with a standard DMM. I believe the large solder pad under the transistor also functions as a heat sink so air wiring one won't work well. Just make sure you heat it up more so you fully melt the solder before attempting removal again. If you don't tear the trace you're still totally fine.

Couldn't find a small heat gun locally so I rolled the dice and replaced the transistor today with an iron (much more cautiously this time).
https://cimg7.ibsrv.net/gimg/www.mia...3803bccab1.jpgWent for test drive and it ran right again. Right up until my heater house blew open :D

Never knew these SMD solder heat gun things existed. Pretty cool.

Thanks guys.

Well done sir.

I have the same SMD heat gun, but it's not at all necessary for this stuff. A 2 speed heat gun like set on low works incredibly well for this sort of thing.