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2014 2.5
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Discussion Starter #1
Hello all,

I have been stalking this site for a couple years now and never had a problem finding a solution...until now. Scrolling through hundreds of posts and I can't figure out why I am getting a P0171 code and such high LTFT. I do have a CAI installed and thought there might be a vacuum leak causing the CEL but after hooking up a smoke machine there was no leak, the LTFT goes down to about 18% when going above idle. The vehicle has is a 2014 2.5L with 151k, spark plugs were changed at 100K, 02 sensors haven't been touched and I have historically ran cheap gas with techron every few thousand miles along with cleaning the MAF sensor. My next thoughts are fuel pump, fuel filter or injectors, possible misfire. I do need to replace the valve cover gasket due to an oil leak form cylinder two, would this cause a fouled plug that could trigger the CEL? I've attached the sensor numbers from my app at 1500 rpm, thanks for any and all help.
482326
482327
 

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2006 Subaru SUS
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Did all this start after the cold air was installed?
I bet if it was returned to stock you'd see good results.
 

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2010 Outback 3.6R 2014 Legacy 2.5i 2003 Legacy L special edition (retired to backup)
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937 Posts
I ended up replacing my intake gaskets to solve that issue on my 2014 Legacy with 50K miles on it. problem has not returned since.
 

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2014 2.5
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Discussion Starter #4 (Edited)
Did all this start after the cold air was installed?
I bet if it was returned to stock you'd see good results.
About 2k miles after the install. Unfortunately the stock intake got thrown out by mistake, so before I drop $$ on a stock I want to check other options.

I ended up replacing my intake gaskets to solve that issue on my 2014 Legacy with 50K miles on it. problem has not returned since.
Did you replace the throttle body gasket? Replacing them this weekend
 

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2014 2.5
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Discussion Starter #5
Replaced all the gaskets on the manifold, installed the stock intake. Took this snapshot going down the road at 45mph, numbers were still the same at idle as the earlier post, any ideas?
482652
 

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2001 VDC/SC One of a Kind
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So the best thing to do for posting data is to run a log. If your app will record and save it in a spreadsheet format or graph, that would help. I'd need to see a couple minutes of each: idle, cruising at 55-60 mph and the a mid throttle acceleration from 40-60 or so. Blue Driver will record data and you're able to save and send it via email, text, etc. You'd post it here as a pic if it's a graph. Best to post a csv somewhere off site and link it here for us to download and look over.

The most common of this type of issue absent a vacuum leak is an old AF sensor. If you look at you first pair of pics where you have the RPM up close to 1500 and no load, the AF is reporting lean while the ECM is adding fuel over it's fuel map. How old is the AF sensor?

Then there's the battery and grounding. If the battery is weak or the grounding corroded or loose, you get all kinds of various issues. Poor grounding will affect feedback from sensors. Poor ampere flow will slow things down like a low battery on you phone or laptop.

LOG: RPM, TPS, ECT, AF VOLTAGE, AF CORRECTION, AF LEARNING, REAR O2, KNOCK CORRECTION, INJ PULSE, MAF, MAP, IAT ans ENG LOAD.

If your app won't log these, look in to ROM Raider. RomRaider - Open Source ECU Tools | RomRaider / RomRaider You will need a Vag-COM KKL 409.1 cable to use to interface ROM Raider with the car.

The CAI should not have caused this if it was connected tight. I will add that unless you had the air intake for the CAI outside the engine bay you actually had an HAI, hot air intake. Engine bay temps get above 120F even in cold weather.

This being an FB engine, does it have sufficient oil in it? The AVLS needs a good oil level to function and the AVLS effects breathing.

I've not run in to failed injectors on an FB engine since it's introduction and I've seen them with mileage up to 190k in various cars including the BRZ and it's twins. Fuel filter, could be an issue if you've been running cheap gas.

This engine also runs better on high octane. I don't care what the OM says. It's more responsive and less knock which results in less fuel and timing correction.
 

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2014 2.5
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Discussion Starter #7
Thanks for the quick response, i'm using car scanner pro but it doesn't have alot of those logs in it. I also have blue driver but need a new obdii because my current one does not connect. The AF sensor is the original, the battery is about a year old and the terminals look fine and are tight, no corrosion and engine oil is good. There is a valve cover leak that I will be taking care of this week along with new plugs. Once I buy/borrow another scanner I'll run those logs
 

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2010 Outback 3.6R 2014 Legacy 2.5i 2003 Legacy L special edition (retired to backup)
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About 2k miles after the install. Unfortunately the stock intake got thrown out by mistake, so before I drop $$ on a stock I want to check other options.


Did you replace the throttle body gasket? Replacing them this weekend
no as I smoked the car and found the leak, verified with small squirts of brake cleaner with engine running afterwards.
 

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Discussion Starter #10
no as I smoked the car and found the leak, verified with small squirts of brake cleaner with engine running afterwards.
ok. I hooked up a smoke machine but there were no leaks, i'm still replacing it just to be sure. Couldn't hurt
 

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2014 2.5
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Discussion Starter #11
Only took 13 days for shipping but got the af sensor installed, still same values. Checked voltage on the male end, clockwise starting at the top right 5.1v, 0.0v, 25.8v, 4.2v, i've done alot of research but can't find out what the voltages should be, I feel like one should be just 12v. Does LTFT take a certain mileage or time until it reads correctly or is instantaneous? Havent gotten the CEL in over 1000 miles so the next question is, should I even be worried about this?
 

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'10 3.6R Outback Limited, 2zr swapped Toyota Yaris track toy, '12 Mazda3 skyactive
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LTFT will take a short while to change (I dont remember the exact time off hand)

However your STFT should be almost opposite to your LTFT if you fixed the issue. For example if you have a vacuum leak and your LTFT is 25%, then when it is fixed your STFT should read -25% or close to. Eventually your LTFT will come down closer to zero and your STFT will level off.

Any mechanics out there feel free to correct me but this is how I've always understood it
 

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2001 VDC/SC One of a Kind
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The long term trim is based on the overall learning curve the ECM makes to keep the engine running proper and is calculated on a time and average.

The short term trim is the immediate changes made to keep the fuel at Lambda in closed loop fueling.

Anytime you make a repair that is an affect to fueling and engine management, when it concerns codes set on the ECM or otherwise you clear the codes and drive it normally, monitoring for changes in performance or possibility for codes.

When you reset the codes, fuel trim is generally reset. If there are no codes set in short time, the ECM will continue to learn how to manage the engine and most times that means STFT will look normal while LTFT may be in double digits. As time passes with miles driven, as long as STFT stays normal then the LTFT will stabilize and come closer to zero.

There are a lot of factors involved. Mainly the VE of the engine, type of fuel, condition of the combustion chamber, spark plugs, grounding efficiency and your foot.
 

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Discussion Starter #14
Great. My STFT is almost zero and will go negative at times but it is very consistent with my '15 legacy that has 30k on it and both STFT and LTFT are less than 5%. I have been running 93 for the last 1500 miles, new plugs, and replaced all the gaskets. I figured it was an average over time but wanted to make sure. I am going to continue to monitor both trims and hopefully they come down in the next thousand miles. If not i'll be spending the $$ on the bluedriver obdii and logging what was suggested earlier in the post
 

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2014 2.5
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Discussion Starter #15
CEL with the same code has came back a couple times and LTFT is constant. New plugs, manifold and throttle body gaskets, oil level is good, and new a/f sensor. Where to next? I used my friends snapon solus scanner and logged everything from the earlier post, still trying to get it on the computer ($%$% mac, probably need a pc). Is there anything else to check? I have been trying to figure out how to check the fuel pressure since its maybe a weak pump.
 

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2001 VDC/SC One of a Kind
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STFT will fluctuate. Normal is +/- 7% or lower depending on weather and altitude.

LTFT should be the same.

Lambda of 1 is 14.7:1. Lower is rich, higher is lean. The ECM regulates the catalytic converter by constantly changing rich to lean. WOT puts the car in OL fueling and you will run rich, as much as Lambda .800. Off throttle and cruising the fuel is cut and the lambda will be up to 1.4xx.

During WOT the STFT and LTFT will be 0.00 on your scanner because OL fueling doesn't have a learning curve It has its own fuel map based on direct sensor feedback and engine load calculations.

If fuel trims are high on the positive side then there is either unmetered air getting in, there's an exhaust leak, or the fuel supply has issues. If it's high on the negative side you have a combustion problem and too much unburned fuel is exiting the engine.

Combustion efficiency also relies on a good operating temperature. Your engine should be running between 80-90C. Too low and the ECM may run rich to heat the engine. Too high and you risk detonation and an overheated cat.

All this relies on proper operation of the sensors on the engine. AF, TPS, ECT, MAP, MAF (for those with one), IAT, Knock and O2. The speed of the car and transmission gear/TCC application also determine fueling.
Everything on the car needs good electrical flow. When problems come up, first place to go is the battery and cabling to make sure they are good.
 

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2014 2.5
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Discussion Starter #18
STFT is less than 7% and will normally be around +/- 1% throughout most phases of driving, the LTFT stays at 15%-20% positive during idle, acceleration from 40-60mph and steady cruise at 55mph. MAF sensor was swapped with my 15 legacy and numbers haven't changed, AF was just changed, 02 rear voltage was ~0.8v and had a sine wave on the graph (still working to upload from cardocs suggestions). The ECT goes from mid 80s-the highest of 92C but averages <90C. As far as electrical flow the battery is a duralast gold that is 10 months old. Terminals and connections have no sign of corrosion is there another way to check electric flow or is it just check resistance with the eng off? I will note that I did add a light bar to the car, could this have a weird draw that is messing up the flow?
 

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2001 VDC/SC One of a Kind
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DuraLast???? I cal it DuraCrap. That could be part of your problem, or you got lucky and have a battery that'll keep working cells.

Ampere output measurements at the battery post with the engine off. It should be supplying the CCA it's rated or higher. Conductance through the grounding should be less that .2 ohms. Same with the positive cable and alternator cable.

Have you checked for vacuum leaks?
 
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