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2011 328i Changed fuel pump now have Fuel Trim Faults P0170 & P0174

Discussion in 'E90/E91/E92/E93 (2006-2011)' started by joseph_tutko, Jul 27, 2016.

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    joseph_tutko

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    My 2011 328xi stalled and would not restart. I determined that there was no fuel pressure even though the fuel pump had adequate voltage available.

    I bought and installed an aftermarket replacement fuel pump. After installing the pump I noticed a fuel line had come loose from the in tank pressure regulator. This was the actual failure mode. I replaced the factory installed spring clamp with a screw clamp and buttoned things up. The car immediately started but had a very rough idle for a few minutes. After several restarts the rough idle resolved itself (the engine control system likely balanced the signal to each individual injector). However, the "Service Engine Soon" lamp then came on. This was odd since all service was current. No red service due appeared when I checked engine status. I tried resetting the service intervals but this did not clear the "Service Engine Soon" light. I then used my OBDII scan tool and found faults P0170 and P0174 active and pending for "Fuel Trim Malfunction Bank 1 and Bank 2 respectively. I checked for intake air leaks after the MAF and found none - and didn't expect that I would as the car ran great prior to the in-tank pressure regulator hose blowing off.

    I next rechecked fuel rail pressure and fount it steady at 65 psi. A few online forums said the pressure should be 72.5 psi. Before changing/reinstalling the old fuel pump I thought I would solicit some thoughts from my fellow 3 Series members. Let me know if y!ou encountered or know of this problem
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    charlson89

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    Have you checked your crankcase pressure to make sure it is not to high causing the lean faults? Also do you have N52 engine or N51 sulev?
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    joseph_tutko

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    Thanks for your reply. As to your questions....
    1. I have not checked for high crankcase pressure. Is there a procedure for doing this?
    2. My engine is an N51 sulev
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    charlson89

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    To check crankcase pressure with the engine running remove the oil cap and you should feel slight suction. If the cap is hard to remove and there is a loud suction noise then the separator had failed and will need to be replaced. Since your vehicle is a N51 I would open up the tank again and make sure none of the fuel lines have a minor leak I have seen this before.
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    joseph_tutko

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    Tested crankcase pressure following your instructions. Cap was easy to remove and I felt a slight suction. I inspected the breather hoses for cracks and all looked good. I also opened up the fuel tank (again) and rechecked all of the fuel lines that I could see. All were intact and connected.

    Recall, the rough running all started after I had a no start condition, Prior to the no-start condition the car ran great.

    Being a former mechanic/automotive controls engineer/do-it-yourself guy, I embarked on fixing this myself. Should be easy, right? During my investigation, I found that there was no fuel rail pressure but there was voltage to the fuel pump. Aha! A bad pump. Prior to finding the loose fuel line, I checked fuses and also disconnected the battery ground cable (which I read zeros out any stored parameters).

    I opened the tank where I noticed that the hose to the fuel pressure sensor had come off. I reinstalled the hose along with a new hose clamp. Since I had purchased a replacement fuel pump ahead of time, I installed this as I read that there were some instances of fuel pumps failing. The car immediately started but had a noticeable rough idle that went away when the engine warmed up after 3 - 5 minutes of running.

    When I re-opened the tank to inspect the fuel lines, I also reinstalled the original fuel pump thinking the replacement pump may some how be causing the problem. No change.

    The check engine mil lamp is off, but my scan too shows the following faults pending...
    Misfire - P0300 (multiple cylinders), P0301, P0302, P0303, P0304, P0305, P0306 (Cylinders 1 thru 6)
    Mixture Lean - banks 1 and 2 P0171, P0174A

    Again, thanks in advance for any next step thoughts you may have.
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    charlson89

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    Thanks for the update. How did you check for intake leaks smoke or brake clean? I agree it is unlikely this is the problem of a intake leak since it ran good before the pump issue. BMW does have bulletin about replacing the clip for the pump fuel line did you replace this during the repair? I'm wondering if your having a volume issue for the fuel like it a fuel line cracked and is leaking some of the fuel out back into the tank. If you run the vehicle with the tank open and watch for any bubbles from a leaking line/ cracked line (I've seen this once before)
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    joseph_tutko

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    Since my last post, I rechecked fuel pressure and found that it is only 20 psi! This would explain the poor running after start-up until the ECU compensated.

    I ran the fuel level down to 1/4 prior and reopened the tank. All hoses were connected (even the one that came off last time) and looked in good shape. I ran the engine and there were no signs of any leaks as far as I could tell (hoses snake everywhere many of which I cannot see). Needing to do something, I ordered up a new fuel pump. It will be here tomorrow.

    I will post how installing a new fuel pump turns out. In the meantime, if you could think of anything else, please post here. My biggest fear is that I read some online posts where older 328s had to replace the entire fuel tank for similar issues. I hope that's not the case here.
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    joseph_tutko

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    Changed the fuel pump and inspected all lines that I can see for leaks. Also ran the engine with the tank open and did not observe and bubbles or leaks. Fuel pressure was 22 psi - still very low. Unexpectedly, the car started and stalled a few times and ran rough until the ECM compensated. MIL lamp not on but P0171 and P0174 were pending. Online searches uncovered instances of the in tank fuel pressure regulator malfunctioning. Could not locate any service parts other than some references to having to replace the entire fuel tank when this happens.

    Do you know if the fuel pressure regulator is serviceable? Any other thoughts?
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    charlson89

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    I don't believe the regulator is serviceable on a sulev. Have you checked to make sure the module called EKPS is giving enough amps and volts to the pump? Thats about the only other thing I can think of causing the pump to not create enough pressure.
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    dvenneman

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    My sympathies. Hope you are finding a way to enjoy this one!

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