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Discussion Starter · #1 ·
2004 Outback H6 VDC. 168k miles

RH valve cover gasket started leaking very badly last week. I had access to a hoist last Sunday, so I started in. Got new OE spark plugs to go in at the same time. After a few hours, I had the problem side buttoned up, but I didn't have all day, and the LH side looked harder to do....so I'll get back to it next week.

The old plugs were correct, and looked to be in decent shape. So while it was time to replace them, I didn't expect any difference in how it ran. And indeed, the ~30 mile drive home it drove fine.

Yesterday (Monday), my wife called me saying that it seemed down on power and the CEL was on. Came up a P0171, bank 1 lean. Diagnostic from the FSM on that code is basically checking for intake/exhaust leaks, checking for a clogged injector, then fuel pressure tests.



Here's my thought process:
I'm ASSuming it's related to what I did.
I'm ASSuming it's not wiring, as I don't have any other O2 codes or a misfire.
I think if it were fuel pressure, it would cause an issue on both banks.

The only thing I can think of is the mis-matched spark plugs. But that still seems very odd.


I cleared the code, so we'll see if it (or any others) come back. I am planning to do the other side on Saturday. But in the mean-time, this is bugging me, and I thought I'd bounce it off you guys.
 

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Discussion Starter · #3 ·
I did check the gap, and they were NGK plugs identical to OE.



Partial follow-up:

That code is set from 2 consecutive drive cycles. So I worked on it on a Sunday, drove it home, and the light came on on my wife's trip to work Monday morning (second cycle). I reset it that evening, back again Tuesday afternoon. So that side was reading lean for 6 of 7 drive cycles (the light was already on for Monday afternoon). Reset Tuesday afternoon, and it didn't come back all week.

Saturday, I took the car to work and did the driver's side. I repaired this car from an accident, and actually reinforced a section of frame rail right over the driver's frame rail. This made that project an exceptional nightmare. Took me the better part of 4 hours just to get it apart. Since I only had the hoist for 2 more hours, I opted to just swap the front plug that I could easily get at from underneath, and get the car put back together. I think I can lift the engine enough to do #4 and 6 at home, I'll do that tonight or tomorrow.

I drove it home Saturday, and then we went for a bit of a drive (about 75 miles one way) on Sunday. On that trip, the CEL came on, and it was lean bank 1 AND 2. I reset them, and they have not come back (probably 5 drive cycles).
 

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OBW H6 VDC, Tribeca, XT6
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two lean conditions right after working independently on each side? weird.

swap plugs and COP and see if the "lean" condition moves or stays?

i'm sure you know this, but pulling the valve covers makes spark plugs easy to replace on those H6's.
 

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Discussion Starter · #5 ·
Yep, very strange.


Normally, yes, it is easier. But due to the accident repair on this particular car, there's even less room there. If I'd hadn't had a hard deadline looming, I would have lifted the engine and done the other 2 plugs from above with the cover off, but I had to get the car put back together and off the lift.
 

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Discussion Starter · #7 ·
Time will tell if my lean code(s) come back....


But, I replaced those last 2 spark plugs last night. Super easy from above by lifting the engine. Disconnected the pitch stopper, removed the motor mount nut and exhaust manifold nuts on that side, and a jack w/wood under the oil pan and lifted away. Then I pulled the washer tank, and easily could get to #4 and #6. Probably would have had to pull the battery for #2, but since I'd already done that one....didn't need to.


If my lean codes persist for more than a week or so, than I'll proceed down the FSM diagnostic chart.
 

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01 Outback LL Bean
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Lean code is set when the total fuel trim hits 25%. 25% is pretty significant and generally means there is some sort of issue with fuel or air metering.

You are probably up in the low 20% range and occasionally hitting 25% which trips the light. If you are over 10% most of the time there is probably a lurking issue.

You can buy a Blue KKL cable on ebay for $15 and use FreeSSM to pull the fuel trim data.
 

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Discussion Starter · #9 ·
The code is tripped with "2 consecutive driving cycles with fault". The FSM makes no mention of where the threshold is to have a fault. But yea, it's not a fluke.


I have a FreeSSM cable...somewhere. I've used the torque app with a bluetooth dongle to look at the trims a couple times (when the code was not coming up), and they were single digits.

I can't explain it, but I think it's clear that something about the valve cover gasket job was causing this, as the codes for the respective banks were immediately followed by doing that side.
 

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Discussion Starter · #10 ·
Alright, for future or current reference, or for anyone who would like to brain storm with me, time to actually try to diagnose this...

I'm at work now, and we're supposed to get snow tonight, so I'm just sorting through the details and coming up with a plan. Might not get to actually do anything for a couple days.

I have a FreeSSM cable somewhere....I'll have to really try to find it. Otherwise I have an OBD2/ELM327 bluetooth adapter. I've used Carista and Torque, I just downloaded Piston and OBD Arny in hopes for clearer live data.


P0171 comes up relatively regularly. P0174 (lean bank 2) came on a couple times right after doing that side, and once more in the last couple weeks. In the last couple weeks, I've also gotten a P2097 (Post catalyst trim too rich, interestingly I got this and a P0171 almost simultaneously), and a P0139 (O2 sensor slow response B1S2).

I have an OBX header set on this car, so I'm assuming the downstream codes are unrelated or unreliable.


Diagnostic flow from the FSM on P0171/P0174 is as follows:
1. Check for other DTCs
2. Exhaust leak
3. Intake leak
4. Fuel pressure with regulator vacuum disconnected
5. Fuel pressure with regulator connected
6. Injector clog
7. Injector resistance
8. CTS
9. MAP
10. IAT

Since I have no other symptoms (runs great, no misfire, etc.). I'm pushing the fuel tests to the very back, as I feel that they would have larger symptoms.

I've visually inspected for an intake/exhaust leak. I'll get out a can of brake clean and really check for intake.

I've watched coolant temperature on Torque and it was in line, so I'm thinking that's probably correct. Maybe I'll try to catch it cold sometime to verify.

I guess the next thing is to watch MAP and IAT values for awhile and see if anything seems out of line. Then I'll have to rent or buy a fuel pressure tester. Maybe I'll harrass our BG rep to see if he'll give me a can of 44k fuel injector cleaner....
 

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01 Outback LL Bean
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Your steps look good. I would be zeroing in on fuel pressure test.

You can get a cheap gauge from harbor frieght for $20. You need to unhook the fuel line at the filter in between the engine and splice it in. You will need an extra short piece of fuel line. 5/16" i believe. The harbor freight tool has an inline adapter.

I would also log rear 02 sensor, Engine RPM and Throttle Position Sensor and from a stop floor the car and go up into 2nd gear. In this situation, we would expect the rear 02 sensor to go rich .9V+. If it is leaning out, ie, going to zero, you have a fuel delivery issue. Dry road recommend for this test :)

Harbor Freight
https://www.harborfreight.com/fuel-injection-pump-tester-62623.html

There are similar items on Amazon for $20 to $25.
 

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Discussion Starter · #12 ·
You really think it's fuel pressure? My thought process, is with a platform with known fuel delivery issues (o-ring on the pump assembly), the symptom seems to cause more serious issues before causing a code.


Being a 2004, this has quick disconnect fuel lines, which I think requires a pretty specialized fitting to test the pressure. So I don't think that kit would be of much help (AutoZone has a much nicer version that they'll rent to you....but still no quick disconnect fittings)
 

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You really think it's fuel pressure? My thought process, is with a platform with known fuel delivery issues (o-ring on the pump assembly), the symptom seems to cause more serious issues before causing a code.


Being a 2004, this has quick disconnect fuel lines, which I think requires a pretty specialized fitting to test the pressure. So I don't think that kit would be of much help (AutoZone has a much nicer version that they'll rent to you....but still no quick disconnect fittings)
I think you have a fuel or air metering problem. Does your car have a Mass Air Flow sensor? Can you provide the Freeze Frame Data for the codes? Are Fuel trims high under load, at idle or both?

Run the test I suggested above with flooring it through first gear and tracking Rear 02 sensor, RPM and TPS. If it goes super lean you have a MAF problem or a fuel delivery problem. Best way to diagnose fuel delivery problem is a fuel pressure test.
 

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Discussion Starter · #14 ·
MAP, not MAF.

I can definitely see how a MAP or IAT malfunction could cause it to run slightly lean, but seems to me like a fuel delivery issue (restriction, notorious O-ring, etc.), it typically manifests as running issues. I do plan to test it, but just think it seems unlikely, and as such I'm planning to test the other things.


I have an OBX header, so rear O2 sensor data will probably not be reliable.

The only fuel trims that display on Torque are labeled "Short Term Fuel Trim" and "Fuel Trim Bank 1 Sensor 2", I'm not sure if that's a labeling issue, or what. I downloaded a couple other apps to try, hopefully one of them displays it more clearly. I monitored those 2 for awhile pretty soon after the code showed up, and neither got out of single digits.
 

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Really check your hoses around/to your PCV valve and make sure there are no cracks. And all your other air hoses / main intake hose for leaks. If it's not that bad of a leak it may not present itself as running roughly.
 

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. . . The only fuel trims that display on Torque are labeled "Short Term Fuel Trim" and "Fuel Trim Bank 1 Sensor 2", I'm not sure if that's a labeling issue, or what. I downloaded a couple other apps to try, hopefully one of them displays it more clearly. I monitored those 2 for awhile pretty soon after the code showed up, and neither got out of single digits.
Missing a few!

See attached. This is the list of OBD-based parameters that should be available on an OBD-based reader. Perhaps some, namely the On/Off ones, might not be, but all the fuel trims, sensor outputs, vehicle speed, coolant temp etc, should be.

As many recommend, Romraider can access the Subaru ssm data stream (different from OBD) which can provide a lot more information. Vag-com cable, laptop, and Romraider. Moreover, Romraider will record the data in a spreadsheet file that you can post here for others to review and analyze.
 

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Discussion Starter · #17 ·
Small update.

Of course, haven't had any codes come back in the last week and a half....


I drove the car quite a bit last weekend. First thing, Piston is a much better app for this kind of stuff than Torque. Torque is neat that you can customize a little dashboard with gauges and stuff, but Piston gives a much clearer list of live data. My only complaint of Piston, is that you cannot change from Metric to Imperial units on individual measurements, only for the whole list. This meant that the only way to get it to read MPH and Fahrenheit, the MAP readout was changed to PSI.

Piston also has a clear catagory for Freeze Frame data, which a P0171 should save. So the next time it happens I should be able to read what it was doing.

While I drove it, IATs were all right were I expected them to be, typically a bit warmer than the dash readout (I don't have the fender snorkus, so it's pulling some engine bay air).

MAP pressures were dead in the suggested range, both with the engine off and idling.

short and long term fuel trims stayed pretty low. Occasionally after a large change in throttle, short term would spike to 10-12% (positive after giving it throttle, negative after letting off).

I did notice, that after cruising at speed for a few minutes, the long term trims would both be under 5%, but Bank 1 would hover almost exactly 3% higher than Bank 2.
 

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Discussion Starter · #18 ·
Drove the car 3600 miles to South Carolina and back last week

I had my bluetooth dongle plugged in the whole time, and I checked for codes fairly regularly even if the light was off in hopes of catching something just pending. I did see a couple, one being the P2097, and sensor 2 slow response, but neither confirmed.


I did get the P0171 confirmed at one point, and I got the freeze frame data. Interesting that it happened at idle.
2018-04-10_09-02-38 by Numbchux, on Flickr

But yea, 34.4% short term is the problem. Interestingly, this was after driving for a couple hours, and the short term was only 2.3%, but still consistent with what I've been seeing, about 3% higher than the other side.
 

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A few things (maybe more as I think of it):

Did you get the ground straps reconnected?
The front O2 sensors' harness plug is at the front of the head, are they connected properly?
What condition is your battery? Have you checked the grounding, amperage output, conductance to the block? Do you have the meter to do this?

Idle fuel trim that high indicates that the fueling is too lean or the computer thinks it is. The front sensor feedback helps determine fuel trim. If the front sensor is sending lean values, the ECM adds fuel and the rear O2 sensor sends feedback that does not correlate with the front requirement, the ECM may set a code for a lazy rear O2. Bad grounds or weak battery will cause a slow AF or O2. (It will also cause slow or inefficient solenoid reactions in the transmission, fuel injectors as well as feedback.)

Since this is all after jacking up the engine to do seals and plugs, I am leaning towards your overlooking a small thing. Sometimes small things create large issues.
 

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Discussion Starter · #20 ·
A few things (maybe more as I think of it):

Did you get the ground straps reconnected?
The front O2 sensors' harness plug is at the front of the head, are they connected properly?
What condition is your battery? Have you checked the grounding, amperage output, conductance to the block? Do you have the meter to do this?

Idle fuel trim that high indicates that the fueling is too lean or the computer thinks it is. The front sensor feedback helps determine fuel trim. If the front sensor is sending lean values, the ECM adds fuel and the rear O2 sensor sends feedback that does not correlate with the front requirement, the ECM may set a code for a lazy rear O2. Bad grounds or weak battery will cause a slow AF or O2. (It will also cause slow or inefficient solenoid reactions in the transmission, fuel injectors as well as feedback.)

Since this is all after jacking up the engine to do seals and plugs, I am leaning towards your overlooking a small thing. Sometimes small things create large issues.
I did not disconnect any of the ground straps, I suppose I should check them to make sure everything's good, that's a good thought.

The sensor plugs was the first thing I thought of, as I did have them unplugged. But I'm confident they're clean and fully engaged.

I haven't tested the battery, but it hasn't left us stranded this winter....so I can't imagine it's weak. I have access to a very nice battery tester at work, but it's not handheld, so it's a bit of a pain to use unless I have the car in the shop for some other reason.


Maybe I'll swap the upstream sensors side to side and see if the symptoms follow....
 
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