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Thread: 2000 323i fuel trim and misfiring

  1. #1
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    2000 323i fuel trim and misfiring

    I replaced one intake boot and glued a small rip in the other but I'm still getting an intake backfire. Replaced all plugs and coils and still misfiring. What is fuel trim bank one sensor one? Codes are P0300 301 302 303 304 305, P0170 P0173 P0150 and P0118
    Last edited by adupage95; 05-15-2019 at 04:07 PM.

  2. #2
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    Welcome to the Forum!

    Please post all codes and the verbiage that come with each code, that way we know what direction to point you in.

    Also as a bonus, what tool you used to pull said codes.
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  3. #3
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    Replace the other boot too, get more info

  4. #4
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    Replace boots with new,
    follow up with a smoke test of the intake.

  5. #5
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    Apologies if I have misunderstood the question. Bank 1 sensor 1 is the pre-cat O2 sensor for cylinders 1-3. Fuel trim is the ECU adding or taking away fuel so you get the right mixture. When the ECU reaches the limit it can adjust but the O2 sensor says, for example, that the mixture is still too lean, it will throw a code and the SES light will come on. At that point, you know the ECU has thrown the towel in and it is down to you to resolve the issue.

    Having a leak in one of the boots is not good. But you have to ask why a leak in the boot would only affect cylinder 1-3. So as has been mentioned above, more information in needed.

  6. #6
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    Super common codes. Your car needs maintenance. Get an OBD reader that can log LTFT, and share, but I can guess P0171, P0175, and probably two others. LTFTs over 10%

    This means that the O2 sensors are seeing a bad fuel-air ratio after combustion and are telling the fuel system to enrich the mix. Causes:
    1. Fuel delivery - Replace filter if over 60k miles, fuel pump if 150k - you can test if you don't want to just replace the pump - look for 50psi at the fuel rail
    2. Vacuum - Probably several vacuum leaks around the manifold allowing unmetered air to enter the cylinder. The MAF measures the air entering the intake then the computer adds fuel to get the mix right. If air is entering after the MAF it is unmeasured, and the system gets confused. Smoke test, then replace all rubber bits including vacuum lines and caps behind manifold, boots, and all CCV parts if original. Remove and inspect DISA (if it is not hard to remove either replace the unit or dig out and replace the seal). Consider replacing brake booster (won't show on smoke test). Leaks will tend to have a more pronounced effect at low rpm when the air introduced through the leak is a higher percentage of overall air flow.
    3. Pre-cat O2 Sensors - If your O2 sensors are over 100k (pre-cat), replace them. You can try and assess whether they are failing, but some people say they are fine until there is a code and those people are not exactly correct. They are a major cause of lean codes.
    4. MAF Sensor - An item of furious debate. If you are over 150k, replace it with Siemens/VDO only. Don't screw around. Also check the connections thoroughly for fluid intrusion and loose pins. It is often the MAF. It can't be cleaned and doesn't throw codes when it is the source of the issue. If you don't want to buy one, go ahead and sniff around the logs, but remember it is probably the MAF.

    Of course, it could also be:
    1. Switched pre-cat wires
    2. Failing ECM

    Quote Originally Posted by whiskychaser View Post
    Apologies if I have misunderstood the question. Bank 1 sensor 1 is the pre-cat O2 sensor for cylinders 1-3. Fuel trim is the ECU adding or taking away fuel so you get the right mixture. When the ECU reaches the limit it can adjust but the O2 sensor says, for example, that the mixture is still too lean, it will throw a code and the SES light will come on. At that point, you know the ECU has thrown the towel in and it is down to you to resolve the issue.

    Having a leak in one of the boots is not good. But you have to ask why a leak in the boot would only affect cylinder 1-3. So as has been mentioned above, more information in needed.
    It happens all the time - could be that one of the pre-cat sensors is lazier than the other. I wouldn't focus on that, as this situation is very common.

    If the fuel trims are higher when the system is at low revs and correct at high revs it is likely a leak (greater air flow at high-throttle means that vacuum leak is a smaller factor proportionately)
    If the fuel trims stay high, likely a sensor or fuel delivery issue.
    Last edited by harrier; 05-14-2019 at 10:51 AM.

  7. #7
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    Quote Originally Posted by harrier View Post
    If the fuel trims are sharply negative when the system is at low revs and corrects at high revs it is likely a leak (greater air flow at high-throttle means that vacuum leak is a smaller factor proportionately)
    ^Some very good points. But is it possible that you mean if you have an air leak at idle, the STFTs are going to be positive? If they were negative, the system would be reducing the amount of fuel instead of adding to it to compensate for unmetered air. Then as you say, with the throttle open, the leak would be a much smaller proportion of the total air flow so the positive trim would reduce.

  8. #8
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    Yes, LTFT would be positive at idle for a leak. Edited the post. Thanks
    Last edited by harrier; 05-14-2019 at 10:51 AM.

  9. #9
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    Codes are P0300 301 302 303 404, P0170 P0173 P0150 and P0118

  10. #10
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    P0300 random misfires
    P0301 to P0304 misfires on cylinders 1 to 4
    P0170 fuel trim bank 1
    P0173 fuel trim bank 2
    P0150 O2 sensor circuit bank 2 sensor 1
    P0118 Not included in my list for the MS42. Maybe somebody can help with that one

    Adupage95. Your original post seems to have disappeared. But my answer at post 4 refers to bank 1 sensor 1. Has the fault moved? Without the question to refer to, it is a little difficult to give a more detailed answer

  11. #11
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    150 and 118 are new ones the original question was what is the fuel trim ones

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  13. #13
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    Quote Originally Posted by adupage95 View Post
    150 and 118 are new ones the original question was what is the fuel trim ones
    Is it possible that the last one is 1180 and not 0118? 1180 is Bank 1 Sensor 2 slow switching from rich to lean.

  14. #14
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    Dont worry about translating the codes. Focus on the list I put above. Once you figure out leaks, fuel system and sensors, the codes will go away.
    Last edited by harrier; 05-20-2019 at 10:05 AM.

  15. #15
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    No it's 118 I have an app and scanner and when I looking it up it said the lower o2 sensor basically

  16. #16
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    Still doesn’t matter. Look at my message. These codes are very common, and knowing their translation is limited value. You are running lean for diagnosable reasons: focus on fixing that, and the codes will sort out

  17. #17
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    Quote Originally Posted by adupage95 View Post
    No it's 118 I have an app and scanner and when I looking it up it said the lower o2 sensor basically
    The after cat sensors don't control the trims. They just tell the ECU how efficient the cats are. Or more accurately, how efficient they think the cats are. Based on the codes, you appear to have either low fuel pressure/flow or a vacuum leak. Make a list of the items you want to check and go through it methodically. Don't throw parts at it. That's not diagnosis - it is very expensive hit and hope

  18. #18
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    Lean fuel mixture codes indicate an in leak(s).
    Perform a pro smoke test to verify location(s).
    Let us know the results.

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