P0141/P0144 problem solved...

[Jackson42]

We've owned our '03 325iT sport wagon for just under two years and for as long as we have owned it, it has on occasion thrown a P0141 or P0144 (lean bank 1/bank2) code, or occasionally both, and I've never been able to nail them down. Even with no stored codes, these two would frequently be pending. Finally the car started to stumble or have a bit of a flat spot, and it continued to deteriorate, but still gave no code other than these two. So I started chasing down vacuum leaks. It had a couple - a crack in the cam cover and a bad O-ring on one of the ports of the balance manifold, but nothing bad enough to account for the driveability problems. Checked the fuel pressure; it was fine. Replaced the MAF; this seemed to help quite a bit but still it had the occasional stumble or hiccup, and the light would come on with P0141/P0144, although not as frequently.

Yesterday I had a really hard time to get it to start while warm, and it wasn't making enough power to even move the car, so after I had it towed home, I went back to basics and slapped the fuel pressure gauge on it. Zero, zip, zilch, nada. The fuel pump had packed it in.

I slapped in a new pump and the car is behaving itself perfectly. No codes either stored, or pending; perfect performance under all conditions.

I guess I had fooled myself into not suspecting the fuel pump sooner, but every time I put a gauge on it, the pressure was within specification. I got almost 500,000 miles on the fuel pump in my E30, so why would I suspect this pump after a measly 160,000? I cut open the pump this morning and found that the commutator had a groove in it several millimeters deep and the brushes had worn down to about nothing, so I have concrete proof that I've finally fixed the problem.

So here's the message: a lean condition could be either too much air or not enough fuel. If my experience helps just one person avoid having to go through all the grief that I have had with this car, it will have been worth it.

[rbelton]

Solid advice, thanks for posting. Testing fuel pressure is not too hard, certainly easier than smoke testing for air leaks for the average DIY'er. Not everyone has access to a proper smoke machine, but fuel pressure can be tested easily with an inexpensive purchase or rental.