Fuel Trim Woes
 

I've noticed a bit of a fuel trim issue since I installed my Aeroforce gauges. My long trim is consistently between -16 and -20. My short trim is usually between +2 and -7 at idle and when driving with the engine in vacuum. Once I go into boost, my short trim spikes all the way to +24 or more. Boost builds fine and it seems to run fine.

I already boost leak tested it, found a crack in the stock intercooler...replaced it, and my fuel trims still didn't change at all.

Mods:
K&N Typhoon Intake
Catless DP
ZZP Intercooler
ZZP dyno tune

Any idea what's going on here? Another boost leak somewhere? MAF issues? BPV issues? Shitty tune? Injectors? Something else? Looking for some input before I start throwing parts at it.

Get a real logged tune. The tune you got probably didn't compensate for the added mods.

Does ZZP not do any logging when they tune the car on the dyno? They're right around the corner from me so I had them do my tuning. The intake and DP were already on there when they tuned it, so I'd hope they would compensate for that. The only mod I've done post-tune is the intercooler.

Contact zzp and let them know your findings. I'm sure (assuming the tune is the issue) they'd be willing to fix any potential issues with the tune at no charge.

Yeah I emailed them before I replaced the intercooler...they seemed to believe that an end tank was cracked (which it was) but trims haven't gotten any better since upgrading the intercooler. I'll try getting in contact with them again and see what they say.

:r:

Did you reset the PCM after fixing the boost leak?
You should just to let it start fresh.

I haven't. I kind of wanted to see what the short trims would look like without resetting. I'll try resetting the PCM after work today and see if that changes anything.

The trims are learned so you should clear them. The STFT will just correct the stored LTFT until they are happy again. Best to reset.

clear your fuel trims. (i think disconnecting the 12V, or clearing codes will clear fuel trims, and i think there's another method maybe a CPID but i dont know that one and it doesn't sound like you have CAN tools either way so that doesn't matter)

When i was messing around with air filters, i noticed long term fuel trim would settle within something like 30 to 50 miles or even faster, therefore i dont think it's the learned value that's the problem, i think you have extra leaks in the system.
back to the drawing board, find the rest of the leaks.

If there were any changes/repairs made that will affect MAF or MAP, it's always a good idea to pull ecm fuse, effectively resetting it. Monitor from there.

Reset the ECU last night. Within 30 miles of driving, the trims were right back to where they were. Sounds like I need to go hunting for more boost leaks.

Yeah check the entire system for leaks. No way a tune could be that far off.

Boost leak tested again today. Sprayed everything down with soapy water and spent a long time listening but couldn't find any leaks. Out of curiosity I reinstalled the stock airbox and reset the ecu again to see what that would do to the trims. After about 35 miles of driving the LTFT is at -8.5, so that seems to have helped some, but there's still something going on.

Looked for leaks again today...I believe I found one at the upper charge piping coupling. Does this seem like a big enough leak to cause my fuel trim issues?

They always seep air from those stock couplings but you gotta remember that heat will affect these things too. It's possible more leaks will be present at operating temp or vice versa. If you still have stock IC, take it off and pressure test it by itself. And do it underwater if possible. They are prone to developing hairline fractures

The intercooler is from ZZP and is less than a month old, so I doubt that is the issue. I found another very small leak where the brake booster hose goes into the intake manifold, but that doesn't seem to make sense given my fuel trims. After taking another test drive, LTFT is holding steady at -7.8 and STFT hovers around zero until I go into boost, at which point it spikes to +10 or more. These numbers are with the stock airbox installed.

So basically I have a negative net fuel trim when the engine is in vacuum and a net fuel trim near zero or slightly positive when in boost. It seems strange for a boost leak to cause this. Thoughts?