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Old 10-29-2014, 02:16 AM   #1
Registered User
Join Date: Jan 2006
Location: Everett, WA
Posts: 46
My Ride: 2002 325Ci
System too lean...is it the fuel pump?


So, at 321K miles, I am finally experiencing a problem: after replacing the 02 sensors (which have been shot quite a while), I keep getting a P0174 code, "System Too Lean". Once the car warms up, it won't idle without me holding my foot just slightly on the gas (includes when stopping at intersections, a real bit**).

I have to be really gentle on the pedal - if I give it gas just a little too fast, it will tend to jump up to about 1300 rpm, then dip down to around 500 and almost oscillate between the two until I let go and try again smoother, or I kill it first.

So far, I've removed and cleaned the ISC valve, replaced the seal around the DISA, and closely inspected the intake boots, but found none of the cracking reported there by many. I bought new boots, but I have to be honest - after inspection the old ones look okay.

Not long ago it was running terribly, with "Cylinder 5 (or 1, 2, 3...) Misfire with Fuel Cutoff" codes, at which time I replaced the fuel filter/regulator and thought I licked the problem, as it seemed to idle fine, but then gradually, over the course of a week, this weird idle condition has developed.

Weird maybe-related story: after bringing the car to him without it being able to start, a mechanic told me the fuel pump was shot. To his surprise, I told him I'd fix it. I was going to tow it home, but tried to start it, and it ran...just fine. He had done some kind of black magic to get it functional again, apparently without replacing parts (perhaps tapping on the pump with a screwdriver?). I tested my luck and didn't have any problems until now - a full 2 years later.

I don't know if what I'm seeing now and that are related. I rented a fuel pressure test kit from the local O'Reilly's auto, which had an adapter that was questionable in size, but it did attach without leaks. Fuel pressure eventually rose to around 49 psi, but it took about 45 seconds. It dropped right after cutoff. Some people have said fuel pressure should hold after engine cutoff. So, is the fuel pump a good logical next step to replace or am I skipping something?

Thanks for any help!
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Old 10-29-2014, 04:48 AM   #2
OEM ///Member
Join Date: Nov 2009
Location: Fairfax, VA USA
Posts: 23,022
My Ride: 330CiC, M5, X5, E93
321k and a 2002, put a fuel pump in the car, they last about 5000-6000 hours, you do the math. For under $125 for a Siemens/VDO pump with sending unit from www.bmaparts.com and use SPECE30 the pump will be on your doorstep in 2 days or less using standards shipping.

Read the 2nd link below in my signature.

Now is the pump your problem and your only problem, who knows.

CCV needs to be replaced, at a minimum the CCV lower oil return line is shot. Power brake booster may be leaking vacuum. Intake boots should probably be replaced as well.

See the 1st link below in my signature.

Search YouTube for Scotty Smoke test, make sure you test both the intake air path and the crankcase as well for smoke leaks. You can do what Scotty dues or make something from other videos.
Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 10-29-2014, 12:31 PM   #3
Registered User
Join Date: Feb 2014
Location: Cascadia
Posts: 47
My Ride: 2003 325it

May be helpful to also check these areas in synopsis at post #26 ..

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Old 11-06-2014, 10:38 AM   #4
Registered User
Join Date: Jan 2006
Location: Everett, WA
Posts: 46
My Ride: 2002 325Ci
Thanks to both of you for the information! I'm off to find some parts. I'll pose back when (if) I figure it out.

deweys_bmw is offline   Reply With Quote

fuel pump, p0174, system too lean

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