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This is a discussion on Bank 1 Lean ...help within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Originally Posted by mycologist Yes, my understanding is that excessive unmetered air is getting in, so it is burning lean, ...

  1. #16
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    Quote Originally Posted by mycologist View Post
    Yes, my understanding is that excessive unmetered air is getting in, so it is burning lean, so the O2 sensor in the front is detecting that and the ECU is therefore unhappy. If it were metered air, there would be no issue as fueling would compensate.

    I have a similar problem with my 2004 Wrx. It seems to be firing on only 2 cylinders on the passenger side and I'm getting nothing from the drivers side. I purchased it from the auction and it came with no ecu nor air intake box. I put a used ecu from ebay in the vehicle and an AEM air intake. The car has a full NUR SPEC exhaust and AEM air intake and that's about it.

    I had the heads done over by a machine shop as I got the car with a busted timing belt and so this resulted in bent valves. I changed all engine seals, valves, head gaskets, spark plugs, timing belt. crank sensor, map sensor, cam sensor (all brand new parts). The car is dumping a lot of fuel in the oil and so I haven't been driving it, the plugs are filled with gas as well. I also discovered a vacuum leak as the previous owner had a boost gauge, took it out and left a line hanging, I fixed that issue and everything seems to be grounded correctly. What should I do I am sooo fedup and nobody can seem to figure out what the problem is. I did a diagnostic, at first it told me i needed to change cam sensor, crank sensor and map sensor. I changed all of them, now I get a code P0171B-(bank 1 system too lean) and also P0341(camshaft position sensor "A" Circuit Range Performance B1) PLEEAASEE PEOPLE I NEED YOUR HELP BADLY I"M ABOUT TO TOSS THIS CAR. I just really want this problem resolved.

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  3. #17
    Moderator Donkey's Avatar
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    You need to recheck the cam timing.
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    Quote Originally Posted by Donkey View Post
    You need to recheck the cam timing.
    Hey Donkey thanks for your input. I took your advice, went to the mechanic today to look over the timing and it appeared to be fine. Any other ideas?

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    Maybe there is something actually wrong with the camshaft position sensor wiring or the magnets in the cam sprocket.
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    Quote Originally Posted by Donkey View Post
    Maybe there is something actually wrong with the camshaft position sensor wiring or the magnets in the cam sprocket.
    Thankyou Sir. Ok cool I'm going to go check the wiring and see if anything is damaged. I'll keep you posted.

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    OP back again here with an update. I cleaned the MAF, checked the air filter (it looked almost new... the original owner did a full check up at the subaru dealer before I bought it... fluids, plugs, apparently the air filter... the MAF wasn't even very dirty), sprayed around for leaks with carb cleaner, reset the ECU and the light came back on ~50 miles later.
    So, I took it to my mechanic and had him look it over. He did the same things I did, and couldn't fine anything wrong, so he did a smoke test... no leaks. The fuel system also seems to be fine. He called me up while he was driving the car around and said, "This thing drives great, I love this car! ...I can't find anything wrong with it."
    He mentioned it is possible, however unlikely, that the O2 sensor could just be getting lazy. He also said he heard the noise I mentioned coming from the turbo under load, but said it is not a leak and it is probably coming from the turbo itself... a fair assumption considering the car has 125k on it, it could probably use a new turbo. Anyhow, he said it's not burning a drop of oil and there doesn't seem to be anything major wrong, just drive it.

    The light hasn't come back on yet, but I am 99.9% sure it will since he didn't do anything different than I did.
    ...I didn't check that the air filter was set properly or whatever, because I wasn't quite sure what you guys were talking about. Could someone elaborate?
    Past that, I am pretty much out of ideas, other than the possible O2 sensor. ...is there a fuel filter on this car I need to clean or replace? (my other car doesn't have a fuel filter, so fair question!) I've also run a couple bottles of injector cleaner through the system.

    Thanks guys!

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    I've noticed another symptom that may help also. When cruising (not accelerating) every once in a while the car will shudder just a hair. ...as if you barely tapped the brakes, or perhaps just let off the gas a bit.

    I've done my best to research this, it looks like it could be the fuel pump possibly? Any other ideas?

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    Ya, I've read through that a few times, it was one of the best threads I found. Nothing quite seems to match my symptoms, though. I think I'm going to try the fuel filter next. I feel like the car would be running much worse if it were the actual fuel pump.

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    Changed fuel filter and messed with the air box. The tabs definitely were not in properly, one of them is broken a little. ...I put it in properly, and it doesn't seem like it would be in any tighter if that one wasn't broken but who knows.
    Anyhow, initial impression is that it did not do anything to help, even after resetting the ECU. It is a very subtle jerk when cruising, so subtle that I haven't really noticed it in the ~10k miles that I've owned it (though I can remember kind of taking note of it before). It only becomes more noticeable at high speeds >80mph in cruise control with the tach above 3k RPM. It just like the car has a hiccup.
    It doesn't really bother me, I just would like to know what it is to make sure it's nothing pressing.
    Any ideas that might tie these 2 together? ...again, bone stock, only code is po171, cleaned MAF, new air filter, no vacuum leaks, new fuel filter, car runs perfect other than the aforementioned and the idle is perfect.

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    I had this same exact issue with my 04 WRX. I could not figure it out for the longest time. I then changed the filter on my intake and removed the MAF and cleaned it using a can of MAF sensor cleaner. I did this months ago and I have not had any issues since! It also seemed to improve my throttle response and the car idles better now as well.
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    Ya, I will say that my car is running 100% smoother since I have put all this love into it, but the original issue is still not resolved. I have read in a few places that with a bad O2 sensor, highway cruising is what seems to pop the CEL back on. ...we have that in common, and I am beginning to suspect that may be the problem. ...is it possible that the O2 sensor is bad and reading leaner than it should (throwing the code) and causing too much fuel to be dumped in, causing an occasional 'hiccup' at cruising speeds?

  14. #28
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    If -- but only if -- you have exhausted all the other possibilities (leaks, MAF, FPR, intake, and so on) then sure, you may in fact have a bona fide sensor problem. I'd check the wiring first, look for fraying, something intermittent maybe, and then I'd finally suspect the sensor itself.
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