Car backfilres/dies when driving
 

I've got an issue and I'd sure appreciate some help. I've got a '95 running an FM turbo kit, Rev-built MS3, Innovate O2 sensor, Deatchwerks fuel pump, and ID 1000 injectors. The car was running fine until a few days ago as I was returning from a multi-day 500 trip. I'd done about 100 miles on that last day and the engine started acting up as I approached home.

The problem started with the engine stalling at idle. It restarted easily but then the engine died a few minutes later while I was driving..I couldn't get it restarted as the engine cranked but wouldn't fire. I figured I'd blown a main relay so I swapped in a new one and got on my way. I thought that was the end of it until yesterday.

I drove the car again and had the same stalling & no restart issue with the addition of a couple backfires out the tailpipe. This happened after driving about 10 minutes. I replaced the relay again, figuring my new relay was bad, and got going again,

Turns out that's not the case. I was driving today and still had the same problem. I'd swap in one of the relays from yesterday each time the car died and wouldn't restart. The engine started up right away, telling me the relays didn't actually fail. By the end of my drive, the car would run for 3-4 minutes before dying.

I can't think of anything that changed and would cause this behavior. I installed the ID injectors today, so that's a change. Even so, that can't be the cause since this problem happened before today.

Any ideas? I've attached the tune and a log file to help. Is it possible the fuel pump is drawing too much power and causing the relays to overheat?

Thanks in advance for your help...

From the log it looks like the MS is doing everything it can to try to keep the engine running. PWM Idle Duty goes up (& MAP goes up), spark advance increases, Injector PW goes up slightly.. but RPM continues to go down.

Could be a dying fuel pump, but I'd expect your AFR to go lean before stalling - they stay pretty consistent.

Potentially coils overheating?

Thanks very much for the insight. I was guessing the fuel pump was drawing excess electricity, which could overheat the relay and cause it to fail. It seemed like that could explain why another cooler relay would run the engine for a while.

But let's run with your idea for a moment. I've got a Fab9 CoP setup, and although it's been good for a while, I had trouble with the coil driver module early on. gnition Connector 4 Position (PNP-CON-4PIN) Could these behaviors be explained by a failing coil driver module? Perhaps it's overheating the relay and swapping in a somewhat cooler one allows the car to run for a while?

A bit of an update: Today I checked and tightened all the wire connections to the ignition system and lowered the dwell from 3.2ms to 2.5 based upon information I found here. Then I went for a 45 minute drive that would have resulted in numerous stalls yesterday. I'm happy to share that the car did great and I'm hopeful the problem is solved.

Many thanks to Onyxyth for his help understanding my log and suggesting the problem.

Very cool! Glad to hear its running. Hopefully it stays consistent!

I'd like to reopen this thread because the problem reappeared. It's much better than a couple months ago but I'll be driving along and the engine will just die. It seems worse when I drive the engine at high RPMs for a while but that's not always the case. The Fab9 ignition module feels cool when the engine dies so I no longer think that's the issue.

I've always noticed that the main relay is quite hot and swapping in another cooler one lets me drive right off. This wouldn't be such a big deal but it's irritating/dangerous when it happens on the highway or a busy street.

Has anybody run into overheating main relays? Any idea what could be causing it?

Miata main relays are junk

https://www.miataturbo.net/general-m...failure-91002/

Thanks for the link to that thread since I missed it during my search. I've probably blown 20-30 during the 20 years I've had the car. I like the idea to directly wire the fuel pump to the battery via another relay in order to take that load off the main relay. I'll work on figuring that out. Good excuse to learn exactly how a relay works.