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Old 08-26-2013, 09:40 AM   #1
whitewater_ncsc
Scooby Newbie
 
Member#: 366521
Join Date: Aug 2013
Default Help me diagnose a fuel trim issue

Hi everyone,

So I have a bone stock 2010 STI (engine wise anyway) and I have been chasing a fuel trim issue where my learned C and D value becomes really high but other trims are fine.

When my learning D value is pegged like this, the car misfires and feels sluggish at high RPM high load like 4th gear 5k rpm +.

Resetting the ECU and the trims will make the car feel great again with no real learned knock but eventually the trims build back up.

What I have done so far :


1) Monitored it over different fuel tank to rule out fuel, at some point I though it was it but it comes back
2) Swapped my MAF with a friend to see if it was an issue with the MAF but no it still did it.


My next steps :

1) Pressure testing my intake, I don't know what kind of leak would give me the trims that I am seeing. Usually, from what I am seeing, A/B trims are the one that get pegged but that's not the case here
2) Swap my front O2. I am really debating doing this before the leak test because it seems easier to replace but I feel bad about just throwing part at the car
3) I have all the HW to go stage 2 but I have been waiting to fix this before doing it. I could slap eveything on as I also got a wideband and this would probably help me diagnose an O2 sensor failure.


Has anyone had a leak that caused just cruise trim to build up but not idle ? I would assume that since my car doesn't knock, my leak is post turbo ? I still build up boost to target so the leak is likely small ?

I attached a learning view and log, any feedback would be appreciated. I depleted all local knowledge (tuner, best dealership etc). Nobody can help me.

Thanks in advance




https://docs.google.com/spreadsheet/...0E&usp=sharing
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