Welcome to the North American Subaru Impreza Owners Club Tuesday March 19, 2024
Home Forums Images WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC Technical > Engine Management & Tuning > Open Source Reflashes

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.







* As an Amazon Associate I earn from qualifying purchases. 
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 08-26-2013, 09:40 AM   #1
whitewater_ncsc
Scooby Newbie
 
Member#: 366521
Join Date: Aug 2013
Default Help me diagnose a fuel trim issue

Hi everyone,

So I have a bone stock 2010 STI (engine wise anyway) and I have been chasing a fuel trim issue where my learned C and D value becomes really high but other trims are fine.

When my learning D value is pegged like this, the car misfires and feels sluggish at high RPM high load like 4th gear 5k rpm +.

Resetting the ECU and the trims will make the car feel great again with no real learned knock but eventually the trims build back up.

What I have done so far :


1) Monitored it over different fuel tank to rule out fuel, at some point I though it was it but it comes back
2) Swapped my MAF with a friend to see if it was an issue with the MAF but no it still did it.


My next steps :

1) Pressure testing my intake, I don't know what kind of leak would give me the trims that I am seeing. Usually, from what I am seeing, A/B trims are the one that get pegged but that's not the case here
2) Swap my front O2. I am really debating doing this before the leak test because it seems easier to replace but I feel bad about just throwing part at the car
3) I have all the HW to go stage 2 but I have been waiting to fix this before doing it. I could slap eveything on as I also got a wideband and this would probably help me diagnose an O2 sensor failure.


Has anyone had a leak that caused just cruise trim to build up but not idle ? I would assume that since my car doesn't knock, my leak is post turbo ? I still build up boost to target so the leak is likely small ?

I attached a learning view and log, any feedback would be appreciated. I depleted all local knowledge (tuner, best dealership etc). Nobody can help me.

Thanks in advance




https://docs.google.com/spreadsheet/...0E&usp=sharing
* Registered users of the site do not see these ads.
whitewater_ncsc is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 08-26-2013, 09:47 AM   #2
dux10
Scooby Specialist
 
Member#: 235338
Join Date: Jan 2010
Chapter/Region: South East
Location: Georgia
Vehicle:
2002 Faggin Wagon
srp

Default

It is possible to have a small leak that's not really a leak at idle, but with more vacuum place on it, it can become a leak. There's a difference between a boost leak, and post maf leak. A post maf leak can be anywhere after the MAF sensor and could potentially cause these problems. A boost leak is also a post maf leak, but its beyond the turbo. If it leaks between the maf sensor and the turbo, its not a boost leak.

With all of that said, it could be your O2 sensor/s. The rear O2 sensor plays a role in overall fueling correction on the newer cars so keep that in mind.

Steve @ Pullz-On Tuning
dux10 is offline   Reply With Quote
Old 08-26-2013, 11:48 AM   #3
nmlittlebigman
Scooby Specialist
 
Member#: 321409
Join Date: May 2012
Chapter/Region: SWIC
Location: Arrey, NM
Vehicle:
2003 Big Effing Van
7.3L powerstroke diesel

Default

Are you on a stock tune?
Are you running stock intake?
Do you have an o.e.m. maf sensor installed? (some aftermarkets have been known to cause issues). Also check the o-ring for cracks or tears.

With that extreme fuel trim you will probably hear any leaks post maf (if present) when you do your Boost leak test.

Once you leak test and find/fix any leaks install your wideband to rule in/out front O2 sensor.
nmlittlebigman is offline   Reply With Quote
Old 08-26-2013, 12:57 PM   #4
whitewater_ncsc
Scooby Newbie
 
Member#: 366521
Join Date: Aug 2013
Default

Thanks for the prompt reply guys,

As far as the car is concerned :

stock intake, stock maf, stock tune and plugs are maybe 8000km old

So it look like my next step is a leak test. I'd love to hear someone who had similar trim and traced it to a distinct root cause either leak or sensor.

I am still a bit puzzled as to why a vacuum leak would not increase idle trim. My understanding is that the manifold runs higher vacuum at idle than cruise so a leak should impact idle more ? Obviously my understanding must be somewhat flawed, if someone could help correct it that would be awesome too

Thanks
whitewater_ncsc is offline   Reply With Quote
Old 08-26-2013, 01:48 PM   #5
dux10
Scooby Specialist
 
Member#: 235338
Join Date: Jan 2010
Chapter/Region: South East
Location: Georgia
Vehicle:
2002 Faggin Wagon
srp

Default

Quote:
Originally Posted by whitewater_ncsc View Post
Thanks for the prompt reply guys,

As far as the car is concerned :

stock intake, stock maf, stock tune and plugs are maybe 8000km old

So it look like my next step is a leak test. I'd love to hear someone who had similar trim and traced it to a distinct root cause either leak or sensor.

I am still a bit puzzled as to why a vacuum leak would not increase idle trim. My understanding is that the manifold runs higher vacuum at idle than cruise so a leak should impact idle more ? Obviously my understanding must be somewhat flawed, if someone could help correct it that would be awesome too

Thanks
vacuum in the intake manifold yes, but airflow through the turbo inlet (between MAF and turbo) increases. This would be where your leak would be.

Steve @ Pullz- On Tuning
dux10 is offline   Reply With Quote
Old 08-26-2013, 05:45 PM   #6
whitewater_ncsc
Scooby Newbie
 
Member#: 366521
Join Date: Aug 2013
Default

Yup okay makes sense, I was thinking about it this afternoon as well.

Fair to say that the leak could be anywhere from the turbo inlet piping all the way to the throttle body (post turbo, intercooler etc) ?

Thanks
whitewater_ncsc is offline   Reply With Quote
Old 08-27-2013, 12:42 PM   #7
joshuajayg
Scooby Newbie
 
Member#: 323310
Join Date: Jun 2012
Chapter/Region: SWIC
Location: The desert
Vehicle:
2002 WRX Wagon
Silver

Default

I believe he is saying your leak will likely be between the MAF and the turbo. Post turbo leaks under even slight boost will cause your A/F learning to be in the negatives due to less air making it into the combination chambers than the MAF had measured. But before the turbo the air is always under vacuum when you are under load.

Joshua
joshuajayg is offline   Reply With Quote
Old 08-27-2013, 02:05 PM   #8
whitewater_ncsc
Scooby Newbie
 
Member#: 366521
Join Date: Aug 2013
Default

Thanks,

Good point now I assumed that you would never really be learning in boost since you are mostly in OL. Hence why I didn't rule out a post turbo leak.

Does the ECU stay in CL long enough under boost to learn ? If it is so, cool it narrows thing down
whitewater_ncsc is offline   Reply With Quote
Old 08-27-2013, 02:13 PM   #9
joshuajayg
Scooby Newbie
 
Member#: 323310
Join Date: Jun 2012
Chapter/Region: SWIC
Location: The desert
Vehicle:
2002 WRX Wagon
Silver

Default

Quote:
Originally Posted by whitewater_ncsc View Post
Thanks,

Good point now I assumed that you would never really be learning in boost since you are mostly in OL. Hence why I didn't rule out a post turbo leak.

Does the ECU stay in CL long enough under boost to learn ? If it is so, cool it narrows thing down

Mmm, good point, I don't know. I'm not that educated on our fueling habits yet.

Joshua
joshuajayg is offline   Reply With Quote
Old 08-29-2013, 11:25 AM   #10
dux10
Scooby Specialist
 
Member#: 235338
Join Date: Jan 2010
Chapter/Region: South East
Location: Georgia
Vehicle:
2002 Faggin Wagon
srp

Default

The stock tune will keep you in CL well into boost (up to 4000rpm). This is the entire reason why its so dangerous to have one of these cars untuned...

Steve @ pullz-On Tuning
dux10 is offline   Reply With Quote
Old 08-29-2013, 11:37 AM   #11
joshuajayg
Scooby Newbie
 
Member#: 323310
Join Date: Jun 2012
Chapter/Region: SWIC
Location: The desert
Vehicle:
2002 WRX Wagon
Silver

Default

Quote:
Originally Posted by dux10 View Post
The stock tune will keep you in CL well into boost (up to 4000rpm). This is the entire reason why its so dangerous to have one of these cars untuned...

Steve @ pullz-On Tuning
Darned emission nazis.
joshuajayg is offline   Reply With Quote
Old 12-05-2018, 09:42 PM   #12
Subaru2019wrx
Scooby Newbie
 
Member#: 494781
Join Date: Dec 2018
Default little help

sorry i am newb at this forum. not sure how to check for things here.

But i ask it here and see how it goes.
I thought or think i have a boost leak. i been taking dealer and they just check oil and the clamps are on tight. and just shoooo me away.
Finally i told them i would pay for a AFR test.

First off they only did idle AFR which does nothing for me for checking for leak. which i will go tomorrow and have them do.

But my numbers right now for idle are
STFT is. -.08
LTFT is. -7
mass air flow is 2.8
with the formula for calculating AFR it about 15.1

Even just looking at the LTFT that is really low for idle. That almost confirms that i have a boost leak i feel like. but they said anything under 10 is OK. well mines is like 3 away from that. And that "10" percent i feel like is average after idle.

My question is just looking at the numbers is -7 for idle too low. Which make my car run lean.

reason i thought i had boost leak is it feels like it dosent pull like it use to. It back fires at high rpm. and some time take little more gas when clutching in first gear.

if anyone can help me on this. thanks
Subaru2019wrx is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -4. The time now is 02:32 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2024 Axivo Inc.
Copyright ©1999 - 2019, North American Subaru Impreza Owners Club, Inc.

As an Amazon Associate I earn from qualifying purchases.

When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission
Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.