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Old 03-14-2019, 01:56 PM
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M54 running lean question

Hey guys,
I recently talked my GF into buying a 2006 X3 3.0i. Unfortunately I couldn't get any service history but the car is in really nice shape, bought it in phoenix.
First day she drove it on the freeway up hill it was hesitating a bit and finally threw a SES. I just picked up a foxwell 520 and it read "o2 sensor precat bank one".
I ordered 2 new bosch o2 sensors ($105 a piece) and just got them last night.
In the meantime I cleared the code and driving it around town she got another SES. I figured it would be the same but this time 2882 and 2883. Which is "mixture prep bank 1 and 2"
She also has been getting the "check gas cap" from time to time. I'm wondering if it might be the fuel pump.
Any one have any experience with this? I'm thinking just install the new o2 sensors and go from there. Thanks
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Old 03-14-2019, 02:10 PM
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Gas cap looks to be in excellent condition.
Just a gentle suction noted with oil cap removed.
Intake boot looks to be in very good condition with no cracking.
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Old 03-14-2019, 02:16 PM
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The mixture is set based on feedback from the O2s so get those in, clear codes, find reset adaptations in the third main menu I forget the name.

Watch the fuel trim values live once you get the o2s installed.

Try some up hill WOT (wide open throttle) runs see if you get hesitation.

If so than for sure check fuel pressure under load. (usually a little tricky to do but if the pump is weak, usually some quick punches of the throttle in neutral will show drop in fuel pressure)

The computer knows how many milliseconds of fuel to add based on the metered amount of air so when you get lean operation, usually it's a vacuum leak down stream from the MAF sensor but with no leaks it's a good chance the fuel pump is worn out and can't supply full pressure at high demand.
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Old 03-14-2019, 02:26 PM
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i just removed the air filter to check it and its brand new looking bmw filter. Interestingly it looks like whoever installed it didn't get the upstream intake connection back in correctly because its all bent and doesn't want to go back in to the airbox.
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Old 03-14-2019, 02:26 PM
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unfortunately the 3.0 have high rate of failures in all the intake hoses and throttle body mini hoses as the 15 year mark. You can have the vehicle "smoked tested" which is a fancy word for pressurizing the intake and engine block and looking for escaping smoke. Most are the oil separator vacuum (CVCC) lines, cam cover gaskets (This engine is pressurized when running), etc.

DISA valve is another source of concern on this application. See DISA Death rattle

On the gas cap, the issue will it hold a vacuum when applied. Testing the cap with a pump is the method as the seal is internal. Cheap part. The code only knows that when the gas vapor pump runs the line does not hold a predetermined vac level. Is it a line to the tank? The fuel vapor canister and or lines? testing we will go.....

On the O2 sensors, they read a value between two points (Lean - rich) and count the rich/lean cycles. If there "extra" oxygen source upstream (intake side), the engine will run lean always and trip a O2 sensor code. As posted reading the mixture values (fuel trim) will show constant effort of the engine management system to en richen without success. You can read the cross counts live on the Foxwell unit.
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Last edited by StephenVA; 03-14-2019 at 02:51 PM.
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Old 03-14-2019, 02:27 PM
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Quote:
Originally Posted by andrewwynn View Post
The mixture is set based on feedback from the O2s so get those in, clear codes, find reset adaptations in the third main menu I forget the name.

Watch the fuel trim values live once you get the o2s installed.

Try some up hill WOT (wide open throttle) runs see if you get hesitation.

If so than for sure check fuel pressure under load. (usually a little tricky to do but if the pump is weak, usually some quick punches of the throttle in neutral will show drop in fuel pressure)

The computer knows how many milliseconds of fuel to add based on the metered amount of air so when you get lean operation, usually it's a vacuum leak down stream from the MAF sensor but with no leaks it's a good chance the fuel pump is worn out and can't supply full pressure at high demand.
Thanks for this! I will check it
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Old 03-14-2019, 02:29 PM
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What he said about the intake boot. Had to replace both mine and wife's at about 3500/4000 hours. Feel the smaller part of the hose in the wrinkles of the coureggated part. Mine had three large tears. (Was able to use tape to seal while part was coming)
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Old 03-14-2019, 02:44 PM
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BTW it has 152k miles
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Old 03-14-2019, 02:45 PM
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I need to do a vacuum reading to get a baseline so I can post what is a good reading on a 3.0 engine. To help determine what is a poor reading. All of these intake rubber parts are all failing now.

A common Vacuum gauge will show engine intake side, leaks as well as exhaust restriction issues. A combustion engine is nothing more than a air pump in - compress - exhaust. If there are leaks on the vacuum side (Intake low at idle and under load) Exhaust side show up under 2,000-3,000 RPM. A closed/crushed exhaust pipe/converter collapsed display normal vac at idle but drops off like a ROCK under load and RPM increases. Foxwell code reader will show misfires jumping all around cyl 3,4,5 under a snap acceleration test.
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2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green
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Old 03-14-2019, 02:57 PM
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I'm wondering if I should start with replacing the o2 sensors or try more diagnostic work to see if its a vacuum leak. What do you think?
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