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[TWO21]

This is my third BMW. I First owned a 1994 325is, then 2000 328i and now just recently purchased a 2006 X3. Has 65k miles on it and I've already started doing a couple things: new plugs, new belts, OEM alarm, window tint, added aux input, about to do the halogen to xenon conversion (will try to post DIY).

Ran into an issue I've noticed, car seems to surge when in 3rd, 4th or 5th and only above 3k rpms. This only takes place while the engine is hot (running temp), cold start and warming up it accelerates fine. Due to the mileage, I decided it won't hurt to do transmission fluid & filter and transfer case fluid but didn't fix it (shifts better!). Next up was fuel pump and filter, didn't fix the issue. Figured it needed a new filter because the car was only driven 7k or less miles per year and did the pump since I was already in there for the filter. So in an attempt to not throw any more money at it, took it to the dealer who did a free diagnostic on it (bad idea, I know). First they told me it was a tire issue and it's the transfer case binding from different diameter tires. I argued with that and so they started digging a little deeper. Next diagnosis was fuel pump, they're seeing a pressure bleed off after the car is off. Told them it was replaced along with the fuel filter but they won't seem to budge saying that it needs to be replaced. What else could it be? Can my new pump really be bad?

[Onizukachan]

I'm sorry I have no real feedback other than the obvious, it's after to computer goes to closed loop. So it has to be electronic/sensor, not hardware related.

[TWO21]

Originally Posted by Onizukachan

I'm sorry I have no real feedback other than the obvious, it's after to computer goes to closed loop. So it has to be electronic/sensor, not hardware related.

Thanks for the reply! I've been thinking it could be a software issue but still trying to rule out a couple other things.

[TWO21]

Dealer replaced my fuel pump and tested the system. Continued troubleshooting things until they found the pre-cat O2 sensor was bad, it was sending corrupt signals to the computer. Would the bad O2 sensor make the computer talk to the fuel pump differently? I don't think they needed to replace the fuel pump if the issue turned out to be the O2 sensor.

[TWO21]

So after 3 weeks of the dealer having my vehicle, they finally resolved the issue...corrupt values stored in the computer. I know the car will learn and adapt to how you drive and I'm assuming this is what values were corrupt. They tried the fuel pump, oxygen sensor pre-cat, left the battery unplugged overnight to reset, checked coils and plugs, several other things and reset those stored values. I got out of there only paying for 1.5 hrs for the original diagnostic fee.