1.5T Need help diagnosing high negative fuel trims

[kytos]

Hi,

I have an intermiternt issue with my fuel trims. It started since september 2020, one night I noticed partial loss of power and when I looked at tunerview AFR was down to 8 and trims were at -25, parked at the nearest safe place and checked every vacuum line, everything was aparently ok. Since then trims have been hovering between -7 to -15, same issue happened again 2 times and finally today I datalogged (stock tune) since it happened yesterday again and threw a P0172 while datalogging.

Thing I've done trying to solve/diagnose this:

- Check vacuum lines (cutting flow by hand and checking stft changes)
- Check charge pipes for leaks
- changed PCV valve (another issue)
- flashed to stock tune
- moved the MAF sensor cables to see if it is a wiring issue


And I don't know what else to do. MAF readings doesn't seem bad. I'm thinking on leaking injectors but I'm not sure right now what could be causing this.

Attached are the datalogs, too rich is when the ECU threw the P0172 code and the other one is after erasing the code and restart the engine . Any guess?

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[hobby-man]

Almost certainly sounds like leaking injectors to me. Pretty common issue.

 

[CAPTS]

have you touched injector connectors area before or wiring around ecu area ?
sometimes it's just a connection issue & can be related to spark.
for this case of yours some have reported similar issue especially after engine rebuild & connections were not secured.

 

[kytos]

Thanks for the help.

Almost certainly sounds like leaking injectors to me. Pretty common issue.

As I said is one of my suspicions but I don't think this can be intermitent? This morning the trims were perfect (almost too perfect STFT near to 0 and LTFT to -3) after erasing the codes yesterday evening.

have you touched injector connectors area before or wiring around ecu area ?
sometimes it's just a connection issue & can be related to spark.
for this case of yours some have reported similar issue especially after engine rebuild & connections were not secured.

The only connector I've touched is the MAF sensor and from my understanding the datalogs seem correct. I'll check the other connectors but I think if it were spark related or injector connection problem I would have experienced missfires which I've not.

 

[CAPTS]

Thanks for the help.

As I said is one of my suspicions but I don't think this can be intermitent? This morning the trims were perfect (almost too perfect STFT near to 0 and LTFT to -3) after erasing the codes yesterday evening.


The only connector I've touched is the MAF sensor and from my understanding the datalogs seem correct. I'll check the other connectors but I think if it were spark related or injector connection problem I would have experienced missfires which I've not.

it does make the trims go nuts too not only misfires, some have also experienced same thing by modding the fuel system.

 

[kytos]

Next steps: Check injector/plugs/ecu connectors and inspect the Spark plugs. Let's see...

 

[Hondanickx]

To me sounds like spark plugs going bad.This started after your turbo swap right?Could also be injector leaking so i would look into those two options.

 

[kytos]

No, I haven't swapped the turbo. This started randomly and not after a recent mod.

 

[booost]

I'd do a complete boost leak test. Sounds to me like something may have came loose. Even if everything seems tight, you never know where a pinhole air leak could be. Just my 2 cents.

 

[kytos]

Checked the plugs and other connectors, reconnected everything again, everything seems fine. Gapped the plugs at 0.7mm, they were all at factory specs. Haven't had the event again since the first post so it's difficult to diagnose.
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