Troubling STFT after ACE Header install
 

Hello everyone,

I'm posting because I'm currently having some trouble with my fuel trims after a recent ACE A350 header install and STG 2 tune by Delicious Tuning. Any help/recommendations or lessons learned would be greatly appreciated.

I recently installed my ACE A350 header/op as well as a drop in K&N air filter. After a few tune revisions from Delicious Tuning, the car feels amazing and seems like it's driving fine, but my data logs say otherwise. Cruising and Idle seem fine, but when I apply throttle, the STFT likes to jump to ~-20-30%. This specifically only happens under throttle, and then the STFTs return to normal. The LTFTs look great, and I think my AFR looks good but I'm new to tuning and reviewing data logs, so maybe I'm mistaken. Has anyone had a similar experience? All bolts on the header seem to be torqued down properly and to the correct torque, MAF looks clean and I don't see any visible exhaust or intake leaks, but it's possible that there's a leak small enough for me to not notice without a smoke test. I've also checked the bolts and ground on the fuel control module and it checks out.
https://datazap.me/u/jf86/ace-a350-s...0&data=3-21-22
Thank you!

Please tell me you have talked with Delicious about this before coming here and asking.

I have, thanks. They recommended checking my fuel control module for proper ground and ensuring that there aren’t any missing bolts. I checked and everything there looks fine.

I also flashed the ECU back to stock and the same problem exists, leading me to believe it’s a mechanical issue and not related to the tune.

I should also note that I’m getting a lean code P0171 due to the instantaneous jumps in STFT.

How old is the car? Is this the only mod on it?

The car is only 6 months old so I suspect if there’s a mechanical problem, it occurred during the install. The header/op and drop in air filter are the only mods. I suspected it was an exhaust leak but double checked the torque on the bolts after a few days of driving/logging and they looked good. I was accidentally a little rough on the O2 sensor cables when removing the stock header (the cable was snagged in the engine bay and I didn’t realize) but there’s no visible damage so I don’t want to replace the sensors if my problem isn’t characteristic of a bad sensor/cable.

I haven’t seen any posts from anyone else that shows healthy fuel trims except for STFT under throttle so I’m at a loss. My best guess is that it’s a small leak somewhere that is so small it only leaks under throttle, but I’m hoping someone else has experienced something similar before I start blindly replacing parts. My next step will probably be having a mechanic leak test the intake/exhaust, then replacing O2 sensors if I don’t receive recommendations to try something else first.

Thanks!

Pretty normal for stft to move round a lot on large sharp throttle movenents that normal

Well there you go, looks like @steve99 has a point. I mean everything else in your log looks perfect, so it makes sense that nothing should be wrong. Are you engaging the throttle fairly quickly as Steve describes?

Thanks for your reply! I agree that it’s normal for STFT to move around quite a bit under throttle, but it deviates so much that it triggers P0171 and puts traction control on until I clear the code. I’d say that’s definitely not normal, but if it’s not unhealthy then maybe I’ll just have to live with clearing codes every time I drive. It does only happen when I very quickly engage the throttle.

Ah yes, the code... definitely odd. I would blame the tune for missing some small detail, but I would have they have gone over that by now. Maybe shoot for one more revision out of them and see if it solves the issue? I had a weird problem myself for a while that triggered P0171 along with a couple other C-codes (very similar setup to yours). For me, the solution was the tuner updating RaceROM on his end, as mine was up to date. Otherwise we spent a bunch of time trying to find the problem, but couldn't. No codes any longer, so I would bet it's just something funky with the tune. The 2017+ cars have some hiccups from what I've read with the more updated software and tunes.

Make sure all the studs are in place still at the header to OP flange. I did the same- checked torque after a few days, all good. Some unknown time later I lost at least one. Might have been two, or maybe the second was later... Don't even recall.