2004 E46 with Check Engine Light - Running Lean

[Andrew D]

2004 BMW E46 Ci with 100,050 miles.

This crazy car keeps giving me the check engine light and tells me it's running lean. I believe the codes are 071x, but I'll correct after checking it again. I've replaced some lines between the air filter and the fuel injector and cannot find anything else. Each time I check under the hood, tighten the clamps, check hoses, find nothing amiss, and cancel the codes. Now a few days later the check engine light is again lit.

The air filter is fresh. Could it be a partially clogged fuel filter restricting flow? Could it be the sensor needs replaced? Is it the sensor in the line just behind the air filter assembly? Thanks for any help you can provide.

[Griffin562]

Could be that your fuel filter's clogged or a sensor's gone kaput. Given the mileage and what you've already checked, looking at both could be your next step. Get a pro to take a look if that doesn't sort it out.

[Sapote]

I've replaced some lines between the air filter and the fuel injector and cannot find anything else.

There are no lines (what kind of lines?) between filter and injectors. Do a smoke test to find the leaking hoses or whatever, not leaking lines.

[Andrew D]

Thanks for the replies thus far. The codes it gives me are:
1/3 P0174 System Too Lean Bank 2
2/3 P0171 System Too Lean Bank 1
3/3 P0174 System Too Lean Bank 2

I am not sure how a smoke machine might work in this case. Will I really be able to see the smoke being drawn into a small crack or crevice? Not disagreeing, just discussing how this might work. There really isn't anyone around here to take it to, unless I go to Greenville, SC or Augusta, GA. I'm about halfway between the two cities. I feel like the BMW dealer will charge way too much.

When I said lines, I should have said hose or ductwork. I had replaced, because I found a crack, the hose that extends out the back of the air filter. Is the sensor of concern right behind the air filter box or further down the line? It all seems to be in good condition and clamps are tight.

BMW Under Hood.jpg

[Sapote]

I am not sure how a smoke machine might work in this case. Will I really be able to see the smoke being drawn into a small crack or crevice? Not disagreeing, just discussing how this might work.

Search youtube to learn how to do a smoke check -- pumping smoke into the intake manifold and into the valve cover (open the oil filler cap for smoke to fill in, then close the cap and continue to pump smoke until seeing the smoke leaking out.

You should use OBDFusion app on phone and OBD reader dongle to create a log file with long tern and short term fuel trim to verify the air leak causing the lean codes.

[E39 Newbie]

You have an obvious vacuum leak. You must employ a smoke machine if you want to get a good test. They are not terribly expensive on Amazon. There are all kinds of places you can get a vacuum leak besides the intake book. VC gasket, VC cover bolt grommets, DISA valve, ICV valve, just to name a few.

[Andrew D]

I've now watched a few videos of using the smoke machine and understand how that would work. I saw another video of a guy squirting carb cleaner around the engine plumbing and such until the engine revved up. I might first give that a try.

I'm having two problems with this car, the other is discussed here.
https://www.bimmerforums.com/forum/s...4#post30926904

[Andrew D]

In January, when I was working on this, I removed the hose that is the fuel vent and plugged the fitting. The check engine light has not returned. So, I suspect this vent line may be damaged or disconnected on the other end. It's difficult to trace beyond where it goes over the transmission area.
During my checking on this I couldn't pull a vacuum on this line, it was free flowing, which would have contributed to the check engine light alerts.
BMW Engine Line.jpg

BMW Engine 2.jpg

[E39 Newbie]

It goes to the fuel pressure regulator, IIRC.

[Andrew D]

Thus far the check engine light alert has not returned. It seems it was the now disconnected hose allowing too much draw, maybe the hose is cracked or disconnected from the other end. I'm going to get that checked out whenever I can get the car to the Greenville SC dealer.

Thank you for your help.

[Andrew D]

The other end of the hose, in my picture from post #8 above, was disconnected from the fuel filter under the car. This allowed air free flow and triggered on the check engine light codes. The short piece of flexible hose connecting it to the fuel filter had dry rotted and fallen apart.

So, running a smoke test wouldn't have found this unless I had checked under the car and under the fuel filter cover. Just a FYI in case someone else is experiencing the same symptoms. Thank you all for your help.