99 Miata MS3Pro blowing fuse
 

I installed a flyin Miata turbo kit on my car a couple weeks and had it running on a MS3Pro from DIY but now I am having an issue where I keep blowing the F1 fuse on the MegaSquirt. I had the car running on the base map and the only change I made was the injector size to 550. I let the car sit for a week and went out to start it last weekend and the car will crank but not start. I made no changes to the car from when it was running the weekend before. I checked everything and nothing was loose or out of place. I installed the stock ecu as I thought there might have been a problem with the MegaSquirt and the car fired and ran right away. I messaged DIY and they said the fuse on the board might be bad so I checked and the F1 was indeed blown. Order new ones and changed my ground on my wideband from the throttle body to the ecu to see if that was causing my issue. Tried to start the car on the MegaSquirt and blew another fuse. Pulled the MegaSquirt and installed the stock ecu and it started again. I don’t understand how the car would run on the stock ecu but not the MegaSquirt if they share the same ground points. The only electrical items I changed for the turbo kit were the GM Iat and the wideband. Has anyone run into this issue or have any ideas as to what to check? I have checked factory ground points and they are all intact. The car sat in my garage and was not driven during the week between not working. I have put 0 miles on this setup and was letting it sit until my Dyno tune appointment.

Just a wild guess, but maybe a short on the 5V feed for the sensors like TPS?

Checked the voltage at the tps with the throttle closed I was getting about .46 volts and fully open it was going up to around 3.8 so I think that is fine. Checked the resistance on the IAT and it was around 10 ohms which I believe is within range from what I found online. I noticed a humming noise when the key was in the on position and it sounded like it was coming from around the injectors. Is that typical with the deautchworks 550’s or could those possibly be the cause? When I pull the injector fuse the noise goes away so I know it something to do with the injection system. The only issue the car had before I installed the MegaSquirt was a P0421 code for the cat. I installed a full 3” fm exhaust with the high flo cat and disconnected the O2 sensors so I don’t think that could be the issue.

When you replace the fuse, does it blow immediately or does the car start and the fuse blows after it starts? Does it happen every time you start it?

I'm dealing with a similar problem. I've got an MS3Pro and occasionally, right after the engine starts (1-2 seconds), the ECU blows the fuse.

It blows immediately when the ignition is turned to on. I don’t even get a chance to connect to tuner studio or crank the starter. Very frustrating after having the car running perfectly fine and then come back to it a week later and have this mystery issue.

I sent the MS3Pro back to DIY for inspection and they found that at the D15 and D16 traces were blown and then the D6 diode was also blown. I know nothing about electrical components which is why I bought this completed unit from DIY. Matt thought the ECU could have seen a sustained high voltage spike of at least 22 volts that caused these things to go bad. I didn’t smell any smoke or anything weird from the ECU other than blowing the internal fuses constantly. I didn’t notice any voltage issues when I had the MegaSquirt hooked up to TunerStudio but I am hesitant to start the car on the MegaSquirt in fear of blowing something up again but not sure how to diagnose it without trying it out. Before I put the turbo on the car it seemed to run fine other than a battery drain that I have not been able to track down. Due to the battery drain I did have to jump the car with a jump box to get it to start with the MegaSquirt. Would that somehow cause an over voltage that would damage the ecu? Am I able to run the car on the stock ecu at idle and lower rpm to diagnose the alternator and electrical system with the DW 550 injectors or will this cause damage?

The stock ECU can really only idle 305cc injectors, just barely. I would swap in the stock injectors as well if you plan on trying to diagnose this with the megasquirt not installed.

Since the injectors were the only thing changed, it is likely those are the culprit. Are the ones you purchased high or low impedance? I'm an idiot so I'm just guessing, but from reading the turbo faqs the miata uses high impedance, low impedance require a resistor and filing of some tabs.

I installed the FM2 kit from Flyin Miata with the DeatschWerks 550cc high impedance injectors. I bought the MS3Pro from DIY which has been helping me try and figure the issue out based on the damage done to my ecu. I checked voltage at the alternator last night and it was only producing 12.2 volts at 3k rpms. I replaced it a couple years ago with a cheap reman from advance so I have a feeling the voltage regulator might be the culprit. I am going to pull the alternator and get it tested somewhere. Also going to check all grounds again just to make sure I am not missing anything. I read something last night about the iat controlling voltage which could have possibly caused the spike. I installed a gm iat from DIY, is there something i can check on that?

I've not heard of a GM IAT sensor ever failing so that's probably unlikely

I don't understand how an IAT sensor can cause a voltage spike.

Jump starting absolutely can cause one.