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1991 Miata Turbo

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I have a 91 Miata that a customer installed a turbo kit. It is not running. I loaded a base tune and set the sensors, the vehicle ran and I even drove it. Shut it off for a few hours then came back and it wouldn't run again.

No spark in cyl 3 and 4.

The ECU is a Speeduino.

Does anyone have experience with an issue like this?

What firmware did you load on it? On your spark settings, make sure that spark output trigger is set to GOING LOW. If you click file > vehicle projects > project properties > settings > enable hardware test > choose activated. That can help you isolate the problem.


Basetune Miata/MX5 89-95 PNP

If you still have spark on 1&4 then the two likely issues would be a faulty ignitor module or coil, or the speeduino itself is no longer outputting a signal to the ignitor. I'd suggest scoping the ECU outputs to make sure that it's actually providing a signal. If that's the case then it's the ignitor or coil that's faulty.

At one point I had the vehicle running great for about 15 min. Then cylinder 3 and 4 spark stopped working. Then the ecu stopped connecting with my laptop and now we are getting no fuel.

I'm leaning towards a fault with the ecu. I do not like saying the ecu is at fault but everything is leaning towards that as the cause.

before you get too carried away, I'd suggest going over the wiring loom for faults, with an emphasis on connections and grounds - wouldn't b e the first time a connector wasn't clicked home and slowly backed out over time, or an earth wasn't tightened and vibrated loose.

I'm going to go over them, hoping it's just that.

Further to my previous comment, if you have access to an LED test light then you can use this to prove the output from the ECU to the ignitor is there or not.