Excessive fuel use, fuel smell after journey, no fault codes, -ve trims

[Mark Appleton]

My 2001 325i uses more fuel than indicated by the trip computer and smells of fuel after a journey, but presents no fault codes, though the long-term trim is negative on both banks (straight-6 engine). There are never fuel puddles or drips under the car. Also, I can hear the fuel pump squealing when I get to 2500 rpm, or so.

I looked underneath at the fuel filter and noted a broken vacuum elbow to the fuel pressure regulator built into the filter – could the pump be over-pressuring as a result? The filter itself is very old (30,000+ miles), but I don’t know how long the vacuum elbow has been broken. I am replacing the filter/reg later today.

In case this does not fix the issue, should I check for leaking injectors/seals?

Cheers,

M.

• This topic was modified 2 years, 12 months ago by Mark Appleton.

Topic

[Casey C]

The first part made me think o2 sensor, purely based on reading about symptoms of a bad o2 sensor if it’s running rich. Of course, I’m basically a novice so keep that in mind. Also don’t know much about BMW, but on a Honda when I replaced the upstream o2 sensor (no code) it seemed to improve the fuel economy (which had been pretty poor for a while). Hopefully it’s the vac elbow / fuel filter issue only.

[Mark Appleton]

I replaced the filter and elbow and the car no longer smells of fuel after a journey, but the trims have skewed toward positive. I’m told that this is to be expected while the ECU adjusts to the new setup.

I found a full set of pre and post-cat sensors for £35, so I might just change them all – the car has done 82,000 miles, and while 100,000 is the common interval, I’ve already got the tool.

[Author]

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