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?

Sounds like a bad ground.

Thanks RotorNut. Where should I look for a ground fault - inside the ECU, under the hood somewhere, ...?

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.

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.

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?

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.

Could the reboot be screwing up the reading on the MAP and causing it to got pig rich? Is there a Wideband?

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..

Answer: the battery was very slightly loose, enough that hard acceleration would allow the + terminal to touch the metal plate running across it.

How did you finally find that?

I'm thinking, and this is just a guess, that he checked the connections and wires as he was advised to do.

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.

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.

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?

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.















:fawk:

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.

Because the sarcastic answer I got was unnecessary.

Who gives a shit what someone types on an internet forum? I mean how does it really effect you? I didn't read anything sarcastic in his post. He just gave you an opinion and you went off on him is how I see it.

Quit getting your panties in a bind over nothing.

Grace and gentility never go out of style. bye

I think it's time to post nude pictures.

lol @ this thread.
I was being serious when I answered. Because you (PUNKSTALENA) didn't read the thread entirely, you came to the wrong conclusion, and now have made yourself look like an ass.
But if you're going to sell your car because someone was mean to you on an internet forum, I don't know how you'll ever deal with someone else's road rage.

Actually the repair was pretty involved; we only found the problem thanks to some luck. We did check & recheck all the wires around the coils, the ECU, the Link, and everything else in the engine compartment. We took the piggyback out of the circuit and bypassed the electronic boost solenoid. We replaced a plug that looked deteriorated. We scratched our heads at an engine code (P0103 - MAF high input) that we were all pretty sure was a red herring but wanted to be sure. We put a multimeter on several components & compared the voltage drop / lack thereof to the schematic to see which circuit(s) were losing power. This revealed some overvoltage (up to 15.4V at times) that made us wonder if the voltage regulator in the alternator was getting wonky and causing the more sensitive components (ECU, head unit) to complain.

In the end it was the last train of thought that brought us to the battery. We were trying to rig up something that would let us monitor the voltage @ the battery while the car was in motion, when we discovered that the battery wasn't quite secure. Then we noticed the black marks on the metal retaining bar that looked an awful lot like electrical bolts had arc'd thru it. Sure enough there was enough play in there that the + terminal could get within a mm or so of the bracket and spark intermittently.

Hope that settles the debate :jerkit:

Wait, so you did all that testing, but didn't check the connections at the battery first as was suggested when you asked here? Why ask a question on the forum and not follow the advice you're given?