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Old 09-22-2020, 06:50 PM   #1
JoeREX
Scooby Newbie
 
Member#: 508182
Join Date: Nov 2019
Location: Austin, TX
Vehicle:
2006 WRX Wagon
Red

Default High Negative AF Learning, what have I missed?

Howdy y'all. Hope you all can help me trouble shoot this issue.

My AF learning 1 has been creeping negative over the past year and a half and I have researched the forums both here and on romraider and tried all sorts of fixes without any luck. My Learning A1 range is currently bouncing between -11 and -13.5 when I drive it. My B range is -7.03, my C range is -3.56 and my D range is 0 of course since I'm on a COBB OTS stage 2+ tune. I will try to get a datalog that I can post tonight or tomorrow too.

I'm in a 2006 wrx wagon with ~150k miles on it and my current mods are:
Grimmspeed UP, DP, and TMIC
COBB EBCS
Perrin Turbo Inlet
Secondary Air Pump Delete
Accessport

Other than the AF learning ranges, the car drives fine. No weird noises, no noticeable loss of power, no knock, no overheating, no oil consumption, no coolant consumption. Turbo seems to spool a little slow by about 300rpm and the highest boost pressure I can hit is right under 15psi.

It started creeping negative about a year and a half ago around the time I did the secondary air pump delete and has slowly but steadily reached its current values (I just checked the block off plates this weekend and they are on there good, no leaks). Once I hit about -5 I started troubleshooting and different fixes.

From what I've found, it could be a post turbo, pre throttle body leak.
It could be an exhaust leak before the front O2 sensor.
It could be worn out maf/o2 sensors.
It could be that the valves aren't seating properly.
It could be a tired FPR or fuel pump.

Things I've tried:

Smoke tested the intake and exhaust:
Found a leak in the UP and swapped in the GS UP which helped spool and peak boost and power through the whole powerband, but didn't change the AF learning.

Pressure tested the intercooler and found a small leak under boost. Swapped in the GS top mount. Helped with power, no immediate changes in AF learning (Makes sense as it only was leaking when the car was in open loop)

Found a small crack in the inlet near the mouth of the turbo so I swapped it before it became a problem. No immediate discernable changes in any of my monitors.

Bought new MAF and O2 sensors. No changes at all in AF learning.

Tested my fuel pressure: 33-34 at a warm idle, 44 with the hose from the FPR to the intake manifold off. no pressure loss over 10min with the car off. This suggests no leaky injectors and my fuel pressure was in spec, at least according to my service manual.

New spark plugs

Rechecked all my fasteners and gaskets, replaced the bpv to tmic gasket 3 times, smoked tested the car again and pressure tested the new tmic with the new silicon hoses, retorqued the block off plates and everything in the exhaust between the heads and the front O2.

Everything was solid everywhere. It has continued to creep negative at the same rate the whole time. The only thing I haven't checked yet are the valves, but I am not having any other symptoms that would suggest my valves are bad or aren't seating correctly. I am planning to take the header off and check them this weekend anyway.

I am about ready to tune it out and forget about it, but I don't want to use a tune to mask a mechanical issue. Other than my valves, what have I missed where else could I be losing all this air? This is obviously driving me crazy, so I'd appreciate some community input.
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Old 09-28-2020, 07:06 PM   #2
JoeREX
Scooby Newbie
 
Member#: 508182
Join Date: Nov 2019
Location: Austin, TX
Vehicle:
2006 WRX Wagon
Red

Default

Just wanted to give an update in case anyone else is having this issue down the road. Make sure your oil is good. Took it to the shop for an oil change and they weren't able to find anything wrong in the intake or exhaust systems. The AF learning percentages are way better though. Like only -3% in A&B after 40 miles. C was -0.78%. I looked into it and it's not terribly common, but if you are taking short trips and not getting the engine all the way warm, it is possible to get gas in your oil.

I haven't been driving much since COVID and when I do, it's short trips around town. I rarely get into boost anyway. Since I started troubleshooting, I have turned the car on and let it idle while I look for any leaks or anything out of place several times.

If you are having negative fuel trims, check the normal stuff: Intake leak between the turbo and throttle body, FPR, exhaust leaks, valves, ect. BUT also check your oil. I haven't seen that mentioned as things to check in the other threads.

How does gas get into oil? Apparently it happens frequently on most cars, but you burn it off easily. One of the six reasons I found on a website was "Gas is always running down into your oil pan on almost all car engines, more or less. When your oil temperature gets high, the gas will come out as vapor from the engine oil. If you only drive for short distances, the engine oil will not reach a high enough temperature to vaporize the gasoline and you will fill up your oil pan with gas for a while. If this happens, you should replace your engine oil and filter. If you know that you often only drive for shorter distances, it’s recommended to change the engine oil at shorter intervals than normal." - totally ripped from mechanicbase. The reasons they listed are too rich of a fuel mixture, you only drive short distances, bad piston rings, misfires, faulty injectors, and faulty carburetor or setting (does not apply to us)

How does gas in your oil affect your fuel trims? Why does it matter if there is too much gas in your oil? Basically, it decreases the viscosity of your oil. It can then squeeze around your exhaust valves and into your exhaust making your o2 sensor think it sees a rich condition. It then pulls fuel to compensate giving you a lean condition in actuality. Additionally, excess gas in your oil will reduce lubrication on things your oil touches like your bearings and other moving parts.

If you are having negative fuel trims, think about your driving habits. If you are taking lots of short trips, never really getting on it, and sitting at idle for extended periods of time, all symptoms of living in the city, then start your trouble shooting by changing your oil.
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