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Old 05-26-2016, 02:34 PM   #1
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Default Spec Miata ECU Failure

I hope this is the right section for this. A question for you guys running stock ECUs and tracking them.

I am potentially going to buy a spec miata with trailer and use it for a HPDE car and possibly work my way up into more wheel to wheel racing. Before I have been able to go down and see it, the owner (he bought it last fall, didn't get to drive it, needs to sell now) took it for a test drive and the car stalled and won't start. He assumed bad gas, but then diagnosed it as a failed ECU and says "spec miatas do that all the time". I have never heard of a miata ecu failing? Is this a common issue track miatas see? Possibly due to the constant jarring and higher heat applications? I just need to know if this guy is trying to pull a fast one or not as I've never seen a failed ECU. Any help is appreciated.
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Old 05-26-2016, 02:36 PM   #2
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Never seen a failed ECU either.
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Old 05-26-2016, 02:42 PM   #3
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No personal experiences, but I remember hearing some rumblings over at m.net about dying capacitors in the older ECUs. No Spec Miata related, just due to age. Not widespread though.

I'd guess he's pulling your leg, but if you had access to a spare ECU would be easy enough to test.
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Old 05-26-2016, 02:45 PM   #4
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I haven't seen the car yet, but he should be calling me tomorrow or this weekend to let me know if the new swapped ecu fires the car up. My concern is some other underlying issue. Sure an ecu can fail, but i can't imagine its a common phenomenon. Thanks for the reply.
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Old 05-26-2016, 06:34 PM   #5
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plug in another ecu. does it run? yes - bad ecu. no? - not bad ecu.
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Old 05-26-2016, 07:01 PM   #6
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I've seen a 99 ecu that fried itself before. It isn't common, but does happen sometimes.
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Old 05-26-2016, 07:16 PM   #7
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Originally Posted by lightw8 View Post
plug in another ecu. does it run? yes - bad ecu. no? - not bad ecu.
Agreed. But I would be weary of the electrical demons that caused the ECU to get fried.
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Old 05-26-2016, 07:48 PM   #8
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Agreed. But I would be weary of the electrical demons that caused the ECU to get fried.
The failed ECU is a symptom, but what is the problem that caused the failure?

Having cooked an ECU once, the diagnosis was uncertain and the resulting rewire was the only was to be certain that it wouldn't happen again. This experience would make me look elsewhere if it happened to car I was looking at buying.
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Old 05-26-2016, 11:33 PM   #9
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I had a '99 ECU fail about 6 months after it was altered by DP Tune. The stock ECU I bought from a '99 part-out is still working after 3 years of tracking.

Find someone parting out a Miata of the same year and get the ECU, CAM sensor, & Crank sensor. Or get new sensors at your local auto parts store. Or check with a used Miata parts seller like Parts Group or Treasure Coast.
It is more likely that the CAM or Crank sensor went out, they can have heat related failures. See MazdaRacers.com and search for CAM and Crank sensor and CAS. There is a Spec Miata specialist in Wisconsin, Dave Wheeler Advanced Autosports. I have no concept of how far from Milwaukee.
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Old 05-27-2016, 08:21 AM   #10
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Great ideas guys. While I'm not happy to hear some of you had failures, it at least makes me slightly more comfortable that it could have happened and he isn't covered up some other failure he needed time to fix. I have not gotten down to see the car yet, nor has he told me the full diagnosis. I should know a bit more this weekend as to what is going on. EricJ: Ill see if I can track down Dave and see if he has any advice or information he can share, thanks for the tip.
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Old 06-05-2016, 07:00 PM   #11
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Quote:
Originally Posted by Swanpuppy View Post
Before I have been able to go down and see it, the owner (he bought it last fall, didn't get to drive it, needs to sell now) took it for a test drive and the car stalled and won't start. He assumed bad gas, but then diagnosed it as a failed ECU and says "spec miatas do that all the time". I have never heard of a miata ecu failing? Is this a common issue track miatas see? Possibly due to the constant jarring and higher heat applications? I just need to know if this guy is trying to pull a fast one or not as I've never seen a failed ECU. Any help is appreciated.
This is extremely common on Spec Miata cars. The CAM sensor and/or wiring is often at fault. We sell a lot of the pigtail or kit to SM customers.

Here is the Miata specific page:
Ballenger Motorsports - High Performance Electronics

Here is the Miata CAM sensor kit (terms & seals loose for you to crimp) & pigtail (crimped with wire leads) respectively:
Home Shop Connectors / Harnesses Yazaki 3 way Miata CAM Sensor Connector Pigtail
Home Shop Connectors / Harnesses Yazaki 3 way Miata CAM Sensor Connector Kit

Take a new sensor & wiring with you to pick the car up and it should fire.
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Old 06-06-2016, 09:15 AM   #12
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Awesome, thank you for the info, Ill see how everything pans out.
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Old 06-06-2016, 08:57 PM   #13
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Cam sensor failure is pretty common, to the point where I and many racers I know carry a spare.

That won't help if it is indeed an ECU failure though. As the vendor said it was ECU, that diagnosis should be checked out (starting by asking how he arrived at it) before looking at the relays and sensors that can stop an engine.

Tactically, do you want to buy a cheap non-runner you may be able to get going quickly/cheaply, or pay more for the running car? If the latter, wait for him to ring with the good news.
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