BMW M5 Forum and M6 Forums banner
1 - 2 of 2 Posts

·
Registered
Joined
·
1,067 Posts
Could be the Left Sucking Jet Pump which moves (siphons) fuel from the left side of the tank to the right side where the pump is located. If this malfunctions you will have fuel in the left side and the gauge will register as such, but you can't get to it! #7 in this diagram. It's obvious whne you open the tank covers...all the fule is in the left side.

See #7 in this diagram:
RealOEM.com BMW E39 M5 Fuel pump and fuel level sensor
 

·
Registered
Joined
·
1,067 Posts
I believe you nailed it.

I've been driving around for the last couple months using the secret menu fuel table, the shaking and vibration still has yet to return but there is always fuel in the left side of the tank when I go to fill up (according to the display). The left side should always suck done completely first, correct? A few weekends ago at Autozone I met a board member and he was surprised this fuel issue has only happened to me once. Guess this is a common issue?
This whole issue is actually a bit bizarre from my perspective in terms of how "common" it is. There are no moving parts in this assembly. It is just a couple of plastic hoses, connectors, etc. It works through a venturi/siphoning type of action I believe. It happened to the wife's 530i - left her stranded once and then again with both of us (at which point I believed her when she said "see, I told you it still had gas") before I researched it and figured out what the heck was going on. Now, it has ALSO happened in my own car once, but here's the kicker. I have this sloped and slanted driveway where the left side of the car sits significantly lower than the right and I swear that has something to do with it (almost like the gas reverse siphons on the slope or just spills over the hump). I also think these things start to lose their seal over time and this may affect the rate at which the siphon works. The fuel is returned to the left side of the tank by the pump/return and just isn't moved as quickly as it should be to the right side. When the seal goes completely it just won't siphon at all, but until then I think it just gets progressively weaker. Some folks theorize that a weakening fuel pump will result in a similar issue. The return volume is less and thus the siphon/venturi effect is less, etc. I have a new Lef sucking jet "pump" (aka "hoses") sitting in a box in my garage right now - it just hasn't gotten quite bad enough for me to replace it yet. Not a big job though. The most important part is having the tank low on gas so you can get to and see everything easy.

That's my story and I'm sticking to it.
 
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top