ajspellm

I have a 99 Miata with a Flyin Miata turbo kit, deutchsworks 550cc injectors, and ms3pro from DIY. I have been working on the car the last couple months in my free time and have had it running on the ms3pro but keep running into this issue where the car will not start randomly. The last time it did this it was cranking and almost fired but then all the sudden didn’t have spark or rpm signal on the ms3pro. The ecu was connecting to my laptop and I traced it to a faulty crank sensor causing the rpm signal to not sync. Got that replaced and the car fired up. Now a week later I went out to start working on the tune and the car has no spark according to my timing light but this time I have no connection to the ecu at all with my laptop. The red light on the ecu is om so it has power. Laptop has not changed. Cable is from diy. Checked fuses and they are all good. Crank sensor is still brand new. Any ideas why I would not be getting a connection to the laptop from the ecu all the sudden and what could be causing my spark issue?

ajspellm

Looked at the car again today and decided to put the factory ECU in since the MegaSquirt was not responding to my laptop even though the red power light was on. After putting the factory ecu in the car started right up. I did not make any changes to the MS3Pro since it was running last and the car hasn’t been started in a week and had just been sitting in my garage. Is the MS3Pro bad or is there an internal fuse that could have possibly popped? Any suggestions or knowledge as to what could have possibly caused this issue?

Holdor

There are two fuses internally on the ms3 board.

ajspellm

I pulled the board out of the case and found the internal fuses. They look fine to me but I have never worked with this style of fuse before. Are these good or do they need to be replaced?

hks_kansei

Never seen weird fuses like that.
But fuses normally are just the same kind of setup in different shaped cases.

Grab a multimeter and check for continuity, far more reliable than a visual inspection.


I can't use a multimeter for ****, i've burned out two in the past, but I use them to check fuses even if they look ok to my eye.

ajspellm

Thanks for the recommendation. Grabbed my multimeter and one of the fuses tested bad. Placed an order for a couple replacements but unfortunately won’t be here before my Dyno tune appointment Wednesday. I can’t find any local stores that stock a specialty fuse like this

hks_kansei

https://au.rs-online.com/web/c/fuses...e-mount-fuses/

Do you have any electronics shops around? I dare say most would stock at least a few on the shelf. (not sure what the US ones would be, do Radioshack sell components anymore, or have they gone like most of the Aussie ones and just sell cheap Chinese appliances?)

ajspellm

Received my replacement fuses today. Replaced the fuse in spot 71 and reinstalled the MegaSquirt and the car would not start. It cranks but does not start.. Checked the fuse again and 71 blew so I obviously have some under lying issue causing the fuse to blow. I don’t understand how the car was running on the basemap from the MS3PRO and then after sitting a week it won’t start anymore and keeps blowing this fuse. I have searched and haven’t found any obvious issues that would be causing this. The only wiring things I changed with the turbo were the gm iat and the aem wideband. I wired the 5v directly to the MegaSquirt from the wide band and put the ground on the throttle body by the factory ground. Should i ground the wideband to the MegaSquirt? The GM IAT I hooked up to the factory wires. Anything else I am overlooking that could be causing this?

Holdor

From what I've read and how my braineack built ms3 is, you should pull both 5v and ground the wideband on the ms3 itself. Not sure if that would cause your issue, but something to fix. I'd also check your grounds in the car, and check your battery terminals are tight. I once had a slightly loose negative on the battery and it would cause no starts and then once started it would misfire and stall as I would drive. The ms3 could be trying to protect itself and blowing the fuse.

ajspellm

Changed the ground on my wideband to the A port on my MS3pro and now the wideband won’t count high than 4 when it turns on. It will hit 4 and then restart. I assume that would mean the ground to the MegaSquirt is bad? The MegaSquirt uses the factory ecu ground which works fine when I plug the stock ecu in. I hooked the wideband back to my ground on the throttle body and it will heat up all the way and go to the afr readout. Anyone have any other suggestions or run into the same issue?