Troubling STFT after ACE Header install

[Jpf86]

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!

[x808drifter]

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

[Jpf86]

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.

[Dzmitry]

Originally Posted by Jpf86

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!

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

[Jpf86]

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!

[steve99]

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

[Dzmitry]

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?

[Jpf86]

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.

[Dzmitry]

Originally Posted by Jpf86

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.

[cjd]

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.