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Discussion Starter · #1 ·
Ok, I just installed an SAFC2 and a wideband o2 sensor in my 1995 gst, and I'm running into a problem. When I started the car up, it reads 18:1 or so at idle, and will read anywhere from 17:1 to 19:1 up to 5k, where I stopped revving it. I started tuning the car at low throttle, and ended up with settings of +20,+14,+13,+8,+3 at 1000 2000 3000 3500 4500 to achieve a 14.7-14.9 A/F on the wideband.

The problem is that for every hour or so of driving the car, it will run really rich for about 15 minutes of the hour. As in, I'll be sitting at idle, 14.9:1, then all of a sudden it drops to 12:1 or so at idle, and runs at around 11.5/12:1 under load. When I zero the SAFC out while its running like this, the ECU has no problem getting it back into the 14.7-14.9:1 range. It will start running very lean again after a short time (5 minutes tops it seems)

So it seems to me like something is malfunctioning MOST of the time, causing the car to run stupid lean, so I have to compensate with the SAFC, but then when it "fixes itself" it runs rich because I had to add so much fuel down low.

I'm going to try a boost leak test shortly, but I doubt I have a part-time boost leak so we'll see. Any ideas what could be causing this?

Useful info/mods

AFC settings 30% low throttle 70% high throttle, karman, up-right arrow
Stock MAFS
Hard upper/lower IC pipes stock SMIC
14b turbo @ 10psi
stock 450cc
PLX m300 wideband in rear o2 sensor bung, 1v signal to ECU
Coolant temps 220ish (kinda high I know, 180* tstat and water wetter going in tomorrow)
CEL code P0127 - intake air temp to high (I dunno...logger shows 15-20* above ambient)

Thanks for any help!
 

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Isn't your o2 sensor for your wideband supposed to be about 36" down from your turbo? Idt that it would cause this, but yea..maybe. I'm not sure on the exact rear o2 sensor location, but I don't think it's supposed to be used for a wideband. Someone who knows better come correct me please...
 

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hawaiifiveoh said:
Isn't your o2 sensor for your wideband supposed to be about 36" down from your turbo? Idt that it would cause this, but yea..maybe. I'm not sure on the exact rear o2 sensor location, but I don't think it's supposed to be used for a wideband. Someone who knows better come correct me please...
the rear o2 is suppose to go after the cat. the wideband should be 24 to 36 inches away from the turbo, and should not be placed below 2 oclock or 10 oclock if you were to look at the exhaust pipe, cut in half, like a clock. That may be a bit tough to comprehend, but it should make sense....
 

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basically you don't want the probe to be covered in condensation or anything that could interfere with it....
 

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Rear 02 is fine for the wideband. No issues there.
 

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Discussion Starter · #8 ·
Ah, yeah it's not a stock exhaust. There is no cat and the sensor is mounted right after the downpipe flex section about 3, maybe 2 and a half feet out from the turbo. It reads correctly when the car is running its best, so I doubt that is the problem. When it reads 15.5 and up it starts popping and breaking up, below 11 it basically makes no power under boost so I think the sensor is fine.
 

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Discussion Starter · #9 ·
So does any one have any input? I would post a log, but I have evoscan, which is garbage for the EPROM ecu and logs one thing at a time.
 
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