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Old 04-20-2023, 05:12 PM   #1
dshim483
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Default Alternator affecting AFR's?

Hello everyone, For the past year and a half of 07 STi ownership I have been trying to figure out why my afr's bounce around all crazy during idle. AFR's will swing from 13 to 17 and go back and forth and never settle at a nice smooth 14.7. Ive tried everything from a parallel fuel line kit, new afr sensor, new maf etc. I eventually gave up and then decided to make a facebook post asking for help one last time before taking it to a shop.

Someone ended up recommending that I disconnect the green plug on the alternator and let it idle and see if that helps anything. I unplugged it and it idled like a brand new car, like ive never ever seen before. So, I replaced the alternator with a 110A from NAPA and i have to say it is definitely better, but not as good as it was when unplugged. So, has anyone encountered an issue like this? My theory is that a diode in the alternator went bad and started introducing AC Current into the system and messed with the ECU???

I think I will start by checking the wiring in that circuit as well as clean all grounds that I can find. Any more advice would be greatly appreciated!
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Old 04-21-2023, 07:12 AM   #2
rtv900
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it's never going to sit at 14.7 BTW
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Old 04-21-2023, 07:59 AM   #3
dshim483
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it's never going to sit at 14.7 BTW
I know, but it swings all over from 13-17 and never smooths out at AROUND 14.7
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Old 04-21-2023, 09:09 AM   #4
rtv900
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I know, but it swings all over from 13-17 and never smooths out at AROUND 14.7
it will never smooth out at 14.7
that is theoretical PERFECT stoich, no gas engine can run dead on 14.7

and they'll all swing around simply due to how it is read
it's not like reading coolant temp or something, it will never sit stable

is it actually running poorly?
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Old 04-21-2023, 09:50 AM   #5
dshim483
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Originally Posted by rtv900 View Post
it will never smooth out at 14.7
that is theoretical PERFECT stoich, no gas engine can run dead on 14.7

and they'll all swing around simply due to how it is read
it's not like reading coolant temp or something, it will never sit stable

is it actually running poorly?
Again, I know it doesnt sit at 14.7 stoich. Mine oscillates from 13 to 17 back and forth... it doesnt stay in the 14's like yours would.
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Old 04-21-2023, 01:35 PM   #6
blurred
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Quote:
Originally Posted by dshim483 View Post
Hello everyone, For the past year and a half of 07 STi ownership I have been trying to figure out why my afr's bounce around all crazy during idle. AFR's will swing from 13 to 17 and go back and forth and never settle at a nice smooth 14.7. Ive tried everything from a parallel fuel line kit, new afr sensor, new maf etc. I eventually gave up and then decided to make a facebook post asking for help one last time before taking it to a shop.

Someone ended up recommending that I disconnect the green plug on the alternator and let it idle and see if that helps anything. I unplugged it and it idled like a brand new car, like ive never ever seen before. So, I replaced the alternator with a 110A from NAPA and i have to say it is definitely better, but not as good as it was when unplugged. So, has anyone encountered an issue like this? My theory is that a diode in the alternator went bad and started introducing AC Current into the system and messed with the ECU???

I think I will start by checking the wiring in that circuit as well as clean all grounds that I can find. Any more advice would be greatly appreciated!
talk to your tuner....

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Old 04-21-2023, 03:55 PM   #7
rtv900
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talk to your tuner....

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Either that or disconnect that AF ratio gauge

still no indication there's an actual problem in how it runs, just the classic gauge reading issue
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Old 04-21-2023, 08:08 PM   #8
subaru_gc8
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what injectors are you running?
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Old 04-22-2023, 08:09 AM   #9
dshim483
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what injectors are you running?
ID1000. and trust me, afr's are all over, causing misfires from being lean. Only have issues at idle. Tuner cant figure it out. Based on logs, as soon as it is in closed loop, it starts leaning out, fuel correction maxes to plus 25% and misfires. But thereafter fuel trims trends out of range negative as if its running too rich.
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Old 04-22-2023, 11:43 AM   #10
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Originally Posted by dshim483 View Post
ID1000. and trust me, afr's are all over, causing misfires from being lean. Only have issues at idle. Tuner cant figure it out. Based on logs, as soon as it is in closed loop, it starts leaning out, fuel correction maxes to plus 25% and misfires. But thereafter fuel trims trends out of range negative as if its running too rich.
If your tuner is sitting in your car troubleshooting and can't figure it out you don't have a good tuner.... Find one that has actual mechanical knowledge. If this is an "e-tuner" that's also your problem right there ...

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Old 04-22-2023, 12:01 PM   #11
19std
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OP Do you have a log?

Are you the tuner and mechanic?
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Old 04-23-2023, 12:06 AM   #12
Alistairh
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Quote:
Originally Posted by dshim483 View Post
Someone ended up recommending that I disconnect the green plug on the alternator and let it idle and see if that helps anything. I unplugged it and it idled like a brand new car, like ive never ever seen before. My theory is that a diode in the alternator went bad and started introducing AC Current into the system and messed with the ECU???

That green plug does is the sense the system voltage. If the lead is unplugged the alternator will run at 100% output.


Have you load tested the battery? Autozone or whatever will do it for free inside the car. If the battery is more than 4 years old I'd probably replace it anyway.


Have you hooked up a mechanical fuel pressure gauge to see whats happening?


Have you logged fuel pump duty cycle after its done running at 100% and compared it to symptoms?


Full list of mods would help.
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Old 04-24-2023, 02:32 AM   #13
subaru_gc8
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Quote:
Originally Posted by dshim483 View Post
ID1000. and trust me, afr's are all over, causing misfires from being lean. Only have issues at idle. Tuner cant figure it out. Based on logs, as soon as it is in closed loop, it starts leaning out, fuel correction maxes to plus 25% and misfires. But thereafter fuel trims trends out of range negative as if its running too rich.
has it always run bad since you put the ID 1000 on?
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Old 05-20-2023, 10:06 PM   #14
spoolinsti05
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Maybe it's your gauge and or sensors or a exhaust leak... Check hose first... There is a tsb however on the output wire that feeds into the ecu from the alternator. Telling the ecu what voltage the alternator is charging the system at.. good luck! I went through this also. Ended up wiring my entire engine harness repairing high resistant ground wires... Along with finding a electrical drain on sb5 and tracing that back to the keyless entry system... LoL good effing luck broham...


Check all your ground wires. Along the radiator support... I also found bad terminal connections at the fuse junction box.. that I repaired with plyers by pinching the terminals.
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