FM2 w/ Link - cuts out under boost, then remains in "limp" mode until rebooted - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-25-2008, 08:13 PM   #1
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Default FM2 w/ Link - cuts out under boost, then remains in "limp" mode until rebooted

Hitting a strange problem with my '99 (full details in signature link). Often, when accelerating under boost, the ECU will cut off: acceleration comes to a sudden stop, the sound system cuts out for ~1 second, and the computer seems to be put into a "limp home" mode. From then onward, I can't exceed 0 boost/vacuum or the fuel will cut out as if I'd hit the redline. Makes for interesting driving, constantly having to watch the boost gauge until I find a place to reboot the car.

Triggering this condition seems to be more a matter of "shocking" the system than raw boost. I can usually get all the way to peak boost (12psi) and keep it there as long as I don't mash the pedal en route. OTOH, it's easily triggered by making hard shifts that land @ WOT. I've even had it caused by a deep pothole in a parking lot at 5mph.

Anyone heard of something like this? Known fix?
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Old 03-25-2008, 09:18 PM   #2
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Sounds like a bad ground.
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Old 03-25-2008, 09:27 PM   #3
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Thanks RotorNut. Where should I look for a ground fault - inside the ECU, under the hood somewhere, ...?
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Old 03-25-2008, 10:40 PM   #4
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Well, the only reason I said that is because you mention the sound system cutting off for a split second and because jarring the car will cause your problem. I'd say check the connections at the battery first (the battery typically does not power the car after startup, but if you have a weak alternator, it could be). Basically, check your common grounds and power sources first and go from there.
If anyone else has an idea, I'm sure they will post up as well.
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Old 03-26-2008, 12:31 PM   #5
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Agreed, I'd be looking for loose wires. I've seen a situation where a slightly-too-short ground wire would disconnect under big engine movements, cutting power to the ECU. The "limp-home" behavior is weird, there isn't one built into the ECU as far as I know. As RotorNut said, the sound system problem certainly indicates a problem outside the ECU, as the Link has nothing to do with that.

The best way to find wiring problems like this would be to do a wiggle test. With the engine idling, wiggle wires until you duplicate the problem.
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Old 03-26-2008, 12:37 PM   #6
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It's on a '99 i'm guessing he is running the Link in parallel with the OEM ECU..

OEM ECU should have a limp mode, No?
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Old 03-26-2008, 01:20 PM   #7
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D'oh, missed that. My bad. It'll have a Link piggyback.

As far as I know, the OEM ECU does not have a boost-related fuel cut under any conditions.
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Old 03-26-2008, 02:22 PM   #8
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Could the reboot be screwing up the reading on the MAP and causing it to got pig rich? Is there a Wideband?
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Old 03-28-2008, 06:39 PM   #9
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Done some more testing. It now happens every time I reach WOT (whether suddenly or not) in 2nd, and almost always in 3rd. Never happens in 4th or 5th even if I stomp on it and zoom all the way to 100mph+.

I also had someone follow me yesterday night. After I accelerated to the "reboot" point, they said my car started putting out black smoke. I assume that's unburnt fuel, so yeah it's probably running super rich
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Old 03-28-2008, 07:10 PM   #10
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Quote:
Originally Posted by Richard Berg View Post
Done some more testing. It now happens every time I reach WOT (whether suddenly or not) in 2nd, and almost always in 3rd. Never happens in 4th or 5th even if I stomp on it and zoom all the way to 100mph+.

I also had someone follow me yesterday night. After I accelerated to the "reboot" point, they said my car started putting out black smoke. I assume that's unburnt fuel, so yeah it's probably running super rich
Get that thing on a load dyno and trouble shoot it before you eff something up..
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Old 04-07-2008, 06:33 PM   #11
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Answer: the battery was very slightly loose, enough that hard acceleration would allow the + terminal to touch the metal plate running across it.
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Old 04-08-2008, 02:32 PM   #12
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How did you finally find that?
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Old 04-08-2008, 09:11 PM   #13
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I'm thinking, and this is just a guess, that he checked the connections and wires as he was advised to do.
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Old 04-08-2008, 10:31 PM   #14
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It's a good thing you're so brilliant but that had already been done. Wanted to know how it finally became so obvious. Don't answer if you have nothing constructive to say.
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Old 04-08-2008, 11:52 PM   #15
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Actually, if you bothered to read the whole thread and pay attention, you would see the OP never said he checked the connections, only drove it to recreate the symptoms. Please try again.
Oh, and you'll quickly learn that anyone on this forum who wants to answer, will answer.
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Old 04-09-2008, 12:19 AM   #16
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Quote:
Originally Posted by PUNKSTALENA View Post
It's a good thing you're so brilliant but that had already been done. Wanted to know how it finally became so obvious. Don't answer if you have nothing constructive to say.
I love it when a noob shows up and starts telling folks how things work around here.

Answer me this King Douche Bag of The Day. Exactly what was constructive or even relevant to the topic in your post quoted above?
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Old 04-09-2008, 08:24 AM   #17
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Amazing - you ask a simple question and you get not 1 but 2 nasty answers. Nice forum. Thanks for the info.
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Old 04-09-2008, 02:39 PM   #18
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Quote:
Originally Posted by PUNKSTALENA View Post
Amazing - you ask a simple question and you get not 1 but 2 nasty answers. Nice forum. Thanks for the info.
Poor little baby life must be really tough on you. Go have yourself a little cry i'm sure it will make you feel better.















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Old 04-09-2008, 03:14 PM   #19
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Wow - I'm just a young woman trying to find out information so I could learn some things on my own. Didn't realize this was not that kind of site. Thanks anyway. Think it's time to sell my Miata
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Old 04-09-2008, 03:21 PM   #20
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Quote:
Originally Posted by PUNKSTALENA View Post
Wow - I'm just a young woman trying to find out information so I could learn some things on my own. Didn't realize this was not that kind of site. Thanks anyway. Think it's time to sell my Miata
Yep I agree sell the miata and start taking the bus if you are really this sensitive then stay off the internet and the roads.

You were the first one to go off on someone in this thread and I don't think you even realize it.
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