94 Miata - no start no CEL

[brookso]

Hi all, I don't post here often, but I see some of you guys fairly regularly out at autocrosses. I'm the eternal optimist who's been running a white 94R in STR


I went to take the Miata for a drive yesterday morning. The car started as normal, ran for a split second, then died. Subsequent attempts to start result in healthy cranking but no spark. No CEL, even with GND and TEN jumpered in the diag box. I have previously verified that the CEL and diagnostics work while doing some work to diagnose an intermittent issue with warm starts and low rpm stumble.


Things I've checked per the no start guide and some other threads at miata.net:


- 10A room fuse in cabin good
- All fuses in main fuse box good
- EFI relay clicks when reinstalling with key in RUN
- removed EFI relay and jumpered front terminals, no change
- Fans and AC run in ACC
- jumpered fuel pump, can be heard running in RUN, fuel smell in trunk after running
- verified 12v to ECU pins 1A and 1B


I've previously read that my particular failure mode (fires up once, runs, dies immediately) could be explained by the engine shutting down because it can't talk to the ECU. As I understand it this would also prevent the CEL from displaying any codes in diag mode.


So maybe I'm looking at a dead ECU?


I have read that it's uncommon for these ECUs to fail, but I'm also pretty sure that the ECU in this car has been modified. From what I've gathered it spent some time in Louisiana as an STS car before it made its way to the metroplex. The limiter has been moved to 8000 rpm, and I suspect that the AFR has been changed, as I've never gotten much more than 20 mpg and the car has always felt like it runs a little rich. I'm not sure how these mods might affect the lifetime of the ECU.


Anything else I should rule out?

Brooks

[sammm]

Did you check the timing belt?

[brookso]

Did you check the timing belt?

I haven't. Of course this happened 2 hours after I dropped the girlfriend off at the airport for a week long business trip, so I haven't had another set of eyes to check under the oil cap for cam movement. I'll add that to the list, thanks.

[brookso]

Did you check the timing belt?

Ok, I've verified that the cam turns when cranking, so the timing belt should be good. Also pulled the ECU and opened up the case. No obvious scorch marks or blown caps on the board, but I don't really know exactly what I'm looking for.

If this was an issue with coils or CAS and the ECU was working, wouldn't it throw a code?