BMW X5 e53 3.0i

[Xx1mbw]

Hello I have a question about misfire cylinder 4 with deviation bank 1 sensor 1 the car seems fine above idle all 02 sensors are switching.problem starts once car is idle if I disconnect the maf plug I have no engine light on and all seems ok I know the ecm needs to receive info from air entering the the engine and receive info from o2 sensors .is this issue the maf as I have fixed all intake vacuum side of things also is it safe to drive with maf unpluged as I do get engine fail safe message come on the instrument clock when I scanned the car no codes come up for maf sensor just deviation bank 1 thx in advance

[MarcoZandrini]

Unplugging the MAF causes the engine computer (DME in BMWspeak) to run a rich air/fuel mixture. I suspect your engine has vacuum leaks. Typically though, the DME will throw P0171/0174 codes when it can’t compensate for the leaks.m

Do the easy, free stuff first. I recommend swapping the spark plugs between cylinder 4 and cylinder 3, clearing the codes and seeing what happens. If it returns to cylinder 4, then swap the coils between the same two cylinders, clear the codes and see what happens. You could have an injector issue. Also, I’d have the intake manifold professionally smoke tested. Sometimes a cylinder will “react” more to a vacuum leak than other cylinders. Try www.bimrs.org to find a reputable indie shop that specializes in bimmers in your area.

How many miles on the X? Is the fuel pump original? When was the fuel filter last changed? The engine has a fuel pressure test valve on the fuel rail. It looks like a tire valve. Pressure has to be 50psi at all times and under all loads.

[e30luv318i]

If you have miss on cyl 4 you prob have a bad coil/plugs . Vac leaks throw codes for a lean mixture

[MauiM3Mania]

Moved discussion to the model specific area.

[Xx1mbw]

Hi members sorry for late response to your reply s I have been waiting for my new mass air flow sensor to arrive so this morning I put it on and with in 3 mins the engine management light on same old crap random misfires with 02 deviation bank 1 sensor 1 I have tried swapping coils plugs new gaskets all on intake and like one of you mention with maf unplugged the car runs fine with no misfire just the fail safe warning with maf not plugged in I have sprayed all round intake no engine increase

[jayeurobm]

check the pcv valve ,one question the coolant level stays the same ?

[Xx1mbw]

check the pcv valve ,one question the coolant level stays the same ?

All this been took out replaced in January as was the intake manifold gasket all pipes been changed
Fuel filter done chasing this problem in the past I have changed all 02 sensors done the rocker cover gasket last year all plug holes are clean and dry today put brand new maf in thinking this was sending wrong info to the Ecu but same result money light on on idle then misfire but I disconnected the plug on maf and no misfire on idle

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The water level warning will come on every few days but when I check it the float only down half in

[Xx1mbw]

183000 miles on clock I’ve had car 4 years and serviced it with oil change and filter twice a year

[Xx1mbw]

Done a fuel pressure test this morning with engine running pressure 54 psi turn engine off pressure drop to 48 then after 10 mins it was down to 42 psi does this sound like bad fuel pump I have no records whether this is original pump should the pressure stay at 54 psi with engine off and will this cause the money light on while idle with misfire to cylinder 4 with o2 control deviation bank 1 sensor 1 I have replaced all 6 coil packs and plugs from main bmw dealers replace all vacuum pipes and boot to throttle body new intake gasket thx

[Xx1mbw]

So today I checked the fuel injectors for leaking all good pressure test readings 54psi engine running 48psi engine off but the pressure seems do drop even more after 20 to 30 mins would the fuel pump be causing this thx

[flyfishvt]

Your running fuel pressure is good. The car is not supposed to hold pressure forever after you turn it off. Leak down is normal. There is a check for valve in the fuel pump that prevents pressure leak down but it will still leak down over time. Even if the check valve failed completely there's no way for that to cause a misfire.