Slowmiatadude

Okay to sum up the story. I built a diypnp 2 extra 1.5b revision board for my 1995 miata. It was running great and I had tuned the idle in the shop. My afr guage wasnt reading when plugged into the output and input port on the megasquirt I believe it's called the db15. Might be wrong. I'm a complete beginner at electronics and this was my first project with circuitry. I decided to test the outputs I had wired into the megasquirt which were a 12v out ground and the afr guage in. I thought I had them mixed up so I took a voltmeter and tested the 12v out pin by grounding the ground electrode to the car and touching the 12v out from the computer. ZAP smoke came out of the ecu. I tried starting the car but it ran around 8 to 9 afr. I had it previously running around 14.3 or so. So I hopped on tuner studio to confirm nothing had changed and reburned my tune to the megasquirt. Same thing. I then started subtracting fuel from my ve table until the numbers were at 1. It ran around 11.6 afr and when on 0 you guessed it. It doesnt run. I took the ecu out of the case and took the top card off to inspect for burn marks. the ECU looks perfect. I plugged it back in and tested the injectors and coils on the test mode it all checked out and was operational. I even took a timing light and put it on all the separate wires to make sure it was firing on all 4. So did I just pay 500 hundred bucks to here a car idle for 3 days or is there a way to check and diagnose the circuitry on my own.

L4nthonyl

iTrader: (1)

Since its a DIYPNP it's gonna be tough for someone to give you online support without more data. It seems like you shorted something. I would start by taking out the ecu to see if you burnt any traces.

Martin Y

Literally smoke, or is that a bit of poetic licence? I mean, I've accidentally touched 2 pins with a voltmeter probe often enough, and you get a spark and jerk your hand away, but you don't often see smoke. That the car still runs is a positive sign. Is it possible that it's the AFR gauge rather than the MS which is damaged? I'm not clear on whether the gauge is actually connected to the MS at the moment. Are the AFR readings you mentioned all from the external gauge rather than Tunerstudio?

Slowmiatadude

well the guage was not hooked up becuase It doesnt work with it plugged in. It did produce smoke. I did take the board back off and inspect it for burn Mark's and other shorts in the circuit. It looks perfectly fine top to bottom. My afr guage was not in the circuit so I dont believe it was the afr guage. With the tune it was previously idling and running fine with it ran super rich. Should I try to reflash the firmware. I checked the calculated fuel to see if it had changed my injector size but it's still set to 265. any suggestions on what it couldve burned

Slowmiatadude

I have taken the board off and inspected all the connections and see if any burn Mark's were present. There is no signs of shorts or burns. I would like to know what sort of information someone would need to know to help. It's a diypnp 2 extra kit that I bought off diyauto tune. It's a 1.5b board that's built for a stock 1995 1.8. no sequention injection or anything like that. There is nothing added to the board at the moment.

I forgot to mention that my ve table on the idle section is not set to 1 and it still runs very rich.

Martin Y

I guess it depends on how exactly something shorted out. I mean, if you had the meter set to read current by mistake you might have just drawn lots of current from the 12V supply, so in that case I'd trace that PCB track back to see if you can find any problems but more likely you accidentally touched 2 pins together in the 15 pin plug. So what's connected to the pins next to the 12V you were trying to test?

I happen to have a v1.1 board right here, but I'm not sure how much help that'll be as the PCB was relaid between versions.

<edit to add> I might very carefully try to measure 12V on that pin again. Making sure the probe doesn't touch anything else, including the shell of the plug.

Slowmiatadude

the only thing else in the db15 in the afr guage in and a ground. Both of them are in line but the ground is next door neighbor. So I'm sure I shorted the ground and 12v out. So it wont hurt anything if I test from testing the 12v out by grounding the electrode to the car and the touching the 12v out. I'm very skeptical about trying this again. If it reads 12v where should I go from there. It goes to the 12v output right beside the db15

heres a picture for reference. The first pin is going to the 12v 2nd to ground and 3rd to the o2 input.
edit--- I did have the voltmeter set to current. Once again I'm a complete beginner at messing with sensitive electronics. So I have abuslutly no "common sense" when it comes to something like this. I'm still having a hard time wrapping my little electronic virgin mind around this stuff.

Martin Y

Okay, that would explain why it shorted out - instead of having the meter set to read how many volts there were between the 12V pin and ground, it tried to measure how much current could flow if it shorted those two points together. (Most meters make us replug the test leads to switch between volts and current, in part to prevent us doing this, but we've all still done it.)

So long as the MS is still producing 12V at that pin it's not very likely that the MS was damaged badly enough to burn a track out. But if 12V isn't still getting to that output pin, then somewhere between the place 12V enters the board and that 10-pin header where you picked up the 12V, there's a burnt out track. A repair would probably be as simple as finding a terminal where the 12V is still good and making a wire link from there to the 10-pin header, thereby bridging the break, wherever it is.

Slowmiatadude

​I will test the 12v out when I get home. So it's as simple as taking the 12v out off and running a wire from the hole to another "good" 12v put port. that doesnt sound to bad. I really appreciate the help. I'll get back to yall if it doesnt pan out.
edit-- big news I only get 7 volts out of the 12v circuit. There is a 5v output right beside it and it's getting 5volts. Could it still be a damaged "runner" in the board or is it a component limiting or pulling voltage. Would it be safe to jump 12v to the 12v pin and just see what happens. all this stuff is right beside the high side drivers which control in injectors right?

Slowmiatadude

I fixed it. It runs great thank yall so much. wouldnt have been able to do it without your input.

Martin Y

Excellent news. Congratulations.