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Fuel Trim levels off..

carlos181

Passed Driver's Ed
Location
New Jersey
2017 Golf R Manual purchased off the lot brand new at the time. Currently stage 2 as of around early December 2019. Initially went with APR but switched over to 93 EQT Base tune. My mods are as follows:
APR Downpipe, AWE Switchpath exhaust, Cobb SR Intake, Wagner Intercooler, Southbend Clutch Stage 2, 034 Dogbone mount insert. 32k miles currently. Never used any other octane fuel (only 93) and have only went to reputable gas stations. Turbo was never touched and is stock.

I decided to go the custom route with EQT. My first log I sent he noticed the rear O2 sensor reading was throwing off the AFR so he had my disconnect/reconnect, reflash, and send out another log. He then discovered the HPFP was on the weak side and wanted to stay within its limits but that he recommended upgrading so I went with Autotech high pressure fuel pump and waiting to get that installed. When I sent out the next log with the first revision, he noticed my fuel trim levels to be very odd. I did a quick check around the intake and noticed the vacuum line was tucked away and was not connected to the intake. Must of been from when the car was at the shop and was running like that for at least 3k miles. I connected it and resent a log but was still off 13% according to Ed.

I was hoping someone knows or has experienced this and can help me out. Ed said to check for any leaks and if not have the O2 sensor and/or MAF sensor replaced. I really hate to prolong this so I was thinking of just replacing the sensors but then again I don't want to fix something that isn't broken. The HPFP will be upgraded soon so I will have the shop look into it more.
 

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
Most likely seems like bad O2 sensor, but yeah I hate spending money and taking shots in the dark. Only time I've seen my LTFT move significantly was with ethanol blended fuels. I assume you mean MAP sensor in your original post, you can confirm it's reading right by looking at air pressure with key on engine off.
 
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carlos181

Passed Driver's Ed
Location
New Jersey
Most likely seems like bad O2 sensor, but yeah I spending money and taking shots in the dark. Only time I've seen my LTFT move significantly was with ethanol blended fuels. I assume you mean MAP sensor in your original post, you can confirm it's reading right by looking at air pressure with key on engine off.
Was thinking the O2 but wouldn't it have thrown a CEL or some type of code or not necessarily?
 

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
Yeah, if it stopped working completely there's a few different codes it could throw and would be obvious fix. If it just slowly over time became inaccurate it might not. But I've never really seen that be an issue with OEM sensors....but you don't want to make too many assumptions right now in the troubleshooting stage.
 

carlos181

Passed Driver's Ed
Location
New Jersey
Noted, I appreciate it. I'll get the HPFP installed and double check for leaks I might've missed, send a log and go from there. This blows cause I've been going through the process since early December and haven't made any progress. I trust Ed in getting the car tuned exactly right and has been helpful/patient with me. I guess i'll just post the end results and what the culprit ended up being, hopefully soon.
 

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
Exhaust leak maybe? Primary o2 is pre turbo and you haven't messed with that so not likely but.... That could throw off sensor reading too. If just give it a thorough look over if you can't figure out an obvious solution right away. Or I guess in your case you're already having the shop do that.
 

carlos181

Passed Driver's Ed
Location
New Jersey
I'm leaning towards a leak somewhere and I think I overlooked it so while it's in the shop they can check better than I can. I have the most recent log but I have no clue as to what to look for and what may appear to be off. Looking at LTFT % it shows 3 during my 3rd gear pull.
 

carlos181

Passed Driver's Ed
Location
New Jersey
HPFP installed. No vacuum leak was found. Ran another log for Ed just waiting on a response, hopefully a good one ? . If not, next course of action is to possibly change the O2 and/or MAP.
 

ZuMBLe

Autocross Champion
Location
NY
Car(s)
Alltrack 6MT
Exhaust leak maybe? Primary o2 is pre turbo and you haven't messed with that so not likely but.... That could throw off sensor reading too. If just give it a thorough look over if you can't figure out an obvious solution right away. Or I guess in your case you're already having the shop do that.

I would think the chance an exhaust leak is the culprit is unlikely. When cruising, the whole system is pressurized pretty good. Even if you had weirdness at idle because of turbulence, it would straighten itself out again once you cruise for a while.

OP,

Is that +13% or -13%? I would reset the ECU, turn the car on and let it idle for 5 minutes. Check the trims then.
 

carlos181

Passed Driver's Ed
Location
New Jersey
Quick little update..

Since installing the HPFP, I installed EQT’s discharge pipe and TMD package. Drove the car completely empty and added 93 octane from a different reputable gas station. Sent a log to ED and he stated it looked solid. Just waiting on a revision.
 
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