Need help with low rpm stumble on FIC - Miata Turbo Forum - Boost cars, acquire cats.

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Old 02-05-2011, 05:38 PM   #1
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Default Need help with low rpm stumble on FIC

Could use some advice please because this stumble is making me nuts.
I have an rhb5 BEGI/cartech s3 system in my 91 1.6. The kit came with a vortech RRFPR which I installed with a 225 walbro.This turned out to be inadequate at around 6psi once I got the car on the dyno with a tailpipe sniffer. To avoid the lean condition I added an AEM FIC and was able to get as rich as I wanted throughout the rpm range by controlling the pulse width. Everything is tuned pretty conservatively and peaks out around 166hp.
I am very happy with the setup and have ben able street to tune everything but one really annoying quirk out of it.
When I'm at low rpm with moderate load at two spots (about 2800 and 3600) and I put my foot down to go into boost, the car stumbles and bucks like crazy. It almost feels like bad ignition wires which caused me to change them out. There is also nothing crazy going on in the ignition map in case you are wondering. Whats really weird is that it happens at various RPM and load cells each time.
I have tried richening and leaning to no avail and I can't make it go away. It is getting increasingly hard to drive around it.
Has anyone got any experience with this problem or any suggestions?
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Old 02-05-2011, 07:30 PM   #2
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What I would do is setup the f/ic to replace the your mass air flow.
http://forum.aempower.com/forum/index.php?topic=23732.0
That way the f/ic is using the map sensor built into it for controlling all parts of fuel delivery.

That's my suggestion anyways.
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Old 02-05-2011, 08:39 PM   #3
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Is that what you think is causing the stutter? The stutter happens out of boost with only the AFM providing info to the stock ecu. When boost kicks in and the FIC is "adding" fuel, everything runs smoothly.
Oh, one more thing, I'm using 1.8 injectors in the 1.6 motor.
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Old 02-06-2011, 12:13 AM   #4
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Are you substituting a signal for o2 to the stock ecu? That way it's not fighting your FIC as far as fueling goes. Search for olderguy o2 clamp. If you don't have a wbo2 sensor you really should get one. Find out what your AFRs are doing when the bucking happens.
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Old 02-16-2011, 12:40 PM   #5
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Turns out the problem was the FMU. Once it was off and retuned with a set of rx8 injectors., the car started running completely smoothly.
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Old 02-17-2011, 07:24 PM   #6
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I think I'm running a little rich. I'm backfiring a little under vacuum and the car reeks of gas. My idle is also a little rough now.
At this point I have the exhaust bunged for a wideband, but no permanent one in place to tune with.
What is the cheapest way to do this? Do those of you who run an FIC leave a permanent one in place and datalog?
I dont really care for a permanent gauge in the car, but will do this if it's cheaper than getting one to plug into the FIC.
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