[Cyberspace]

Hey guys, I bought a 2008 328i about a month and a half ago, with 95k miles. There were/are a few things that need fixed, and my current struggle is that when I add gas to the tank, it will only fill up to half a tank, and it tends to misfire and/or stall afterwards for a while. I've noticed that if I add gas, and then get on the highway and run it at 80mph for 10 minutes or so, it runs just fine afterwards. It's never misfired above 30ish mph, it runs smooth as a dime above that, it just has problems at idle/low rpms/speeds after I add gas. I've only ever used premium 93+ octane.

I had to have the fuel pump seal replaced, as it would leak a bit after I added gas. I also replaced one of the ignition coils, because it fell apart when I pulled it out. ISTA+ only gives me the error 00CF17, something about the DSC/DME-DDE not sending data to the DKG/EGS.

Does anyone have any ideas about what I can do for the misfires/stalling fuel problem?

[Phil325i]

Was the car standing for a while before you bought it? Maybe the fuel's gone stale? Are you sure it's only half filling? Could the gauge sender be faulty..?

[sabino56]

Originally Posted by Cyberspace

I had to have the fuel pump seal replaced, as it would leak a bit after I added gas.

You mean you could smell gas inside the car after refueling and tracked that down to the fuel pump seal under the rear seat?

Was the 1/2 tank problem there before the fuel pump seal was replaced?
The fuel sender is on that unit and there are a lot of tubes in area. It may be possible that the float is hung up on something if the problem started after messing with the fuel pump.

No ideas on misfire as function of refueling. I suggest you find someone to read codes to narrow that down.
Good luck!

[Cyberspace]

Originally Posted by sabino56

You mean you could smell gas inside the car after refueling and tracked that down to the fuel pump seal under the rear seat?

Was the 1/2 tank problem there before the fuel pump seal was replaced?
The fuel sender is on that unit and there are a lot of tubes in area. It may be possible that the float is hung up on something if the problem started after messing with the fuel pump.

Good luck!

After I "filled" the tank for the first time, I heard liquid hitting the ground, and looked under the car and saw the seal leaking. The gauge only ever read at most half full the entire time I've owned it(about two months now), before and after the seal being replaced. I've heard that the charcoal canister might be the culprit of the tank filling problem, so I'm gonna check it out. I have not had the courage to open the gas tank yet to check the actual level, or the float, but I'm pretty sure the shop that fixed the seal looked in the tank.

I've checked the codes, and there aren't any related to misfires. The only engine code I get is 00CF17, something about the engine not talking to the transmission. My research has lead to the fuel breather valve being the culprit of the misfires, but it doesn't make sense why it happens most after adding gas.

[Cyberspace]

Originally Posted by Phil325i

Was the car standing for a while before you bought it? Maybe the fuel's gone stale? Are you sure it's only half filling? Could the gauge sender be faulty..?

The dealer said he had been driving it personally for about 6 months before he sold it to me, and "hadn't noticed any problems"(what a load of crap). I haven't checked the gauge sender yet.

[Brian86]

I'd bet somebody has already gotten their jam-hands in there and screwed up the gasket, fuel pump, float sensors, and vent lines.

The air vent for filling is right under the cap. It's a little port to the right of the fuel nozzle hole. I do not know precisely how it's interconnected with the expansion tank and main fuel tank but it will be (mostly) independent of the evap/purge/charcoal canister system.

[sabino56]

Yeah, seems like someone messed up when servicing fuel pump or something.

You say you had the fuel pump seal replaced? Confusing thing to me is that whoever did that would have had to pull the fuel pump/sender out to replace that seal. And if the fuel sender wasn’t working correctly because it was hung on something - that person also screwed it up putting it back in? Seems unlikely if the person was competent. Of course, maybe he didn’t replace anything, just found the ring loose and tightened it, said job done.

Regardless, it sounds like starting with looking at fuel pump/sender, the tank there is the place to start. If you don’t do it yourself, don’t take to same person who replaced the seal. I don’t have a lot experience on how the fuel system works other than the pressure side. Maybe a full tank without air inside causes problem in something where a 1/2 tank has enough air it doesn’t?

It’s pretty easy to take a look at the top of the fuel pump/sender. Easy to pull up rear seat and remove the access plate. If you see something wet you know you have a problem. A bit sketchy to open the tank & remove fuel pump to see inside with gas if you are not confident. Better to have someone do it if not confident.
Good luck