hi guys, not here much because the car in question is my wifes and i'm not allowed to modify it, but, apparently i'm allowed to fix it so ..... need some help.

car is a '01 740i

problem, has been throwing a P0171 & P0174 [scantool] code. code is system too lean on each bank. code is intermittant, clears itself an reappears.

things that may be effecting the appearance/disappearance : seems to set more when hot outside and a/c is used. seems to go away when a cycle of tank injector cleaner is used, but not only when used.

got a air pump system code recently and found that the air pump valve vacuum line was cracked, replaced, valve seems to operate correctly as does the pump, that code cleared itself. thought maybe the vacuum leak was causing the lean code as it is both banks.

tried the old spray brake cleaner with one hand and hold the fire extinguisher in the other, couldn't get the engine to change speed and all obvious vaccuum lines seem to be sound.

wondering if anyone had this issue and what ended up being the cause.

other than vacuum i'm guessing fuel delivery, possibly fuel pump pressure or fuel filter ? .of course after reading this site and seeing the cause and effect of german engineering ............ it might be the cupholder sensor ;]

anyway, i need to get this thing smogged and my troubleshooting ability is about tapped as far as this space shuttle is concerned. any help in which direction to go or what to start replacing first is appreciated.

next stop is the dealer or the bmw mechanic . hate to go there if i can just replace the offending part.

ps. just found out that the seat and steering wheel are randomly moving while the vehicle is being driven, it did this once before but stopped for about 4 mos [thought maybe it fixed itself]. anyway, this is obviously not safe, any ideas on what to replace there ? no fault code for that, might be an accident report soon if i don't fix it.

How many miles on the car?

Intake leaks, contaminated MAF, or aged pre-cat O2 sensors are common causes of those codes. It sounds like there aren't any obvious leaks so I'd suspect the O2 sensors next. Useful life of the pre-cat sensors is not more than 100k and they are usually bad enough to justify replacement by 80k.

A hidden form of an intake leak that can be diagnosed by a crankcase pressure check is a failure of the CCV.

thanks for the reply.

sorry 65k miles, should have mentioned that.

is ccv crank case ventilation ? or the normal ,pcv, positive crank case ventilation .

if so where would i find that ? these heads are not your standard v-8 , 6 or i-4 configuration. yeah i know i need to get a manual if i plan on keeping this thing running.

i pulled and cleaned the maf [with maf cleaner] when this started quite awhile back, seemed to have no effect on the frequency of the on/ off cycle of the light.

o2 sensors was one of my guesses, i've had them go bad on other vehicles. generally i would get a fault code on one bank first. in this case i've had both banks from the start, that's why i figured an intake leak.

wondering if the million dollar bmw scanner will give more specific info ?

guess i'll change out the o2 sensors and see if that does the trick

thanks again, any other ideas welcome

e

The CCV is just a more sophisticated PCV. On the M62 engine it is located at the rear of the engine pretty much under the intake manifold.

At that mileage the O2 sensors are possible but unlikely, especially since both codes appeared at the same time. Now that I know the mileage I'm thinking intake leak, CCV,or MAF.

update;

changed out the o2 sensors [precat] ..... that didn't work.

picked up a fuel filter while i was at it, putting that on in a few minutes. [figured i'd do maintenance related things to see if i get lucky]

was thinking maybe the filter was clogged enough to restrict flow, or possibly the fuel pump is on it's way out [though it's running fine]

any idea what the pressure should be at the fuel rail ?

so the ccv is under the intake, any way to check it without pulling the manifold ?

the maf, shouldn't the maf throw a maf related code ? can it be tested ? or is it r&r and hope you didn't just throw away hundreds of dollars ?

do you know of a better way to check for intake leaks ?

we used to use starting fluid when i was younger, dumber. and invinceable, used brake cleaner thinking it should have a similar effect.

i'm running out of time to get it smogged, if i don't get it in the next couple days i guess i'm at the mercy of a "genuine bmw mechanic"

replaced the fuel filter, pulled the maf and cleaned it, drove it about 20 miles, runs great, light is still on, same code. tried my method of vacuum leak testing again, a little more thoroughly and still got nothing.

guess i let the wife put some miles on it and see if i accomplished anything other than a fairly complete tuneup ;]

any help with checking the maf, ccv and a better way of checking for intake leaks is welcome.

For intake leaks visual inspection of all hoses and/or spraying carb cleaner or starting fluid on suspect areas is all you can do outside of a smoke test of the intake system.

Checking the crankcase pressure is the diagnostic for a CCV.

The only practical test for an MAF is to swap it out with a known good unit. While a complete failure of the MAF will result in a fault code, one that isn't correctly measuring airflow won't cause a code. That said, if the airflow measurement is off by a good bit live data from the DME will show the error.

After replacing the O2 sensors you need to clear the fault codes, reset the adaptation values and see if the code returns.

i was hoping if the problem was corrected the code would clear itself, was hesitant to clear it after sensor change as my cheap little actron seems to clear all the evap data for smog. i know that will reset to ready after so many miles so i guess i'll give it a shot.

i've only been spraying the front and top of the motor and as deep under the intake as possible. any vacuum lines anywhere else to check ?

don't really know anyone else with this car so "borrowing" one doesn't seem like an option and i doubt the dealer would take it back once it's out of their site. but that seems like the next step ..... hey it's only money right ;]

thanks for sharing the knowledge, i'll let you know what happens

e

another update;

i reset the mil with my handheld, it cleared all the data so i've been trying to put miles on it to get it to show ready. wife hasn't needed the car so i've been driving it around reading the scan. so far it's cleared 5 of 8 needed for smog ready status.

it's hot here right now and i've noticed that when i have the air on i get the p0171 &p0174 codes pending, i turn it off and drive 5 miles or so and they go away.

so i guess my solution at this point is to drive it far enough without the air on to clear the smog.

question is: what on this car does the computer use to compensate for the additional load of the a/c that might be causing this to happen ? or, are we back to the maf just isn't doing it's job correctly ?

seems that if there was an intake leak the code would not be dependent on the ac being on so it seems like a sensor or maybe relay ? issue.

does that help anyone help me ?

thanks, e

Having the A/C on increases the load at idle, which would make the affect of an intake leak or failed CCV worse. I suppose a contaminated MAF could have the same affect, but its affect should be worse off idle and it shouldn't matter whether the A/c was on or not.

well i've got 175 miles on it since i reset, 6 tests show ready 2 incomplete [catalyst and o2 htr {heater ?} ] not sure what clears these last 2, time, mileage, cycles ?

no recurring lean codes driving with a/c off, i've driven it across the range from idle to wot cars drives perfectly , idles smooth, no hesitation, power is linear with no hiccups.

just need these last 2 codes to clear so it passes smog, then i guess it's off to have a vacuum test of some sort because i really can't find any.

figured i'd end this thread with what ended up happening.

i had reset the pcm/ecu and had been driving the car with the air off too get the computer to show systems ready [for smog check] , i got a couple hundred on it but got sick of driving for the sake of clearing codes. told my wife to just drive it for work and i'd deal with the codes if they reset.

well she drove it with the air on, air off, didn't throw any codes pending or ses light. took about 300 miles to ready the system with the 02 heater being the last to show clear.

so it was either ; the o2 sensors and they needed the computer to be reset to rationalize the data properly. the fuel filter [didn't drive it enough before i cleared the system to know], the maf [i cleaned it again, same story, didn't drive it enough].

i know this doesn't help much but that's what happened.

if the code comes back, the first suspect will be the maf as it was only cleaned and not replaced.