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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 7 Series / 8 Series > 7 Series - E65 / E66 (2002 - 2008)

7 Series - E65 / E66 (2002 - 2008)
Discussion of BMW's 4th generation E65/E66 7 Series flagship. The E65 generated much controversy, due to its radical styling and iDrive user difficulties. Nonetheless, the E65 broke records to become the best-selling 7-series iteration ever, especially after its 2005 facelift.

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  #1  
Old 07-05-2015, 03:58 AM
karl530 karl530 is offline
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Location: Morecambe, UK
 
Join Date: Mar 2013
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Mein Auto: E65 & E31
Low fuel level gives rough engine performance?

I am hoping someone has some insight to this fault my car has, it is a 2008 UK 740i with the N62B40 engine and 49k miles on it.

If I let the fuel level become low, less than a 1/4 tank (approx) the engine starts to become very rough/lumpy. It feels as if the car is almost misfiring but there are no fault codes or cel. This makes the drive very jerky.

If I fill the car full everything smooths out and there is no trouble until the level becomes low again. The fuel pump was changed at the dealer approx 15k miles ago.

Has anybody any thought on what might be causing this or where to look?
I am thinking of starting with a fuel filter change.
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  #2  
Old 07-05-2015, 04:23 AM
lives7rong lives7rong is offline
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Sounds about the right place to start. Next I would check to make sure the fuel pump itself is seated properly with the o-ring, check for sediment in the tank and see if the filter on the pump itself ( not sure if that applies on the e65 ) is seated properly and not clogging anything at lower levels. Also when you're low on fuel get the fuel pressure checked and see if there is a loss.
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Old 07-05-2015, 09:37 AM
Rick in Yuma's Avatar
Rick in Yuma Rick in Yuma is offline
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Location: Arizona
 
Join Date: Dec 2006
Posts: 397
Mein Auto: 05' 760li,94' H1,08'Smart
This is just my thoughts. The gas tanks under the seat are split, by the driveshaft. They have a transfer pipe. That moves fuel from one side to the other, to keep them balanced. If one pipe is shorter or bent it may not balance the fuel properly. Causing air to be sucked into the fuel system. If it was bad fuel you would be having the problem all the time. Unless there are particles at the bottom of the tank that are getting sucked into the fuel system. Then you would have problems with injectors and other small fuel injection systems. This would not be sporadic. My thought is when the dealer replaced the fuel pump. The transfer pipe was incorrectly installed. Again these are just my thoughts I'm not a professional mechanic but I had the fuel system opened up on my 760. And could see where this would be a problem if fuel piping was bent.
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Old 07-05-2015, 08:48 PM
The Magus The Magus is offline
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Location: Vancouver, WA
 
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Mein Auto: BMW 760Li (2008)
It's possible the fuel pump is not properly seated in the tank. It has to be inserted until it clicks into position.

I had the same problem on my old 528i. It would run rough at 1/4 full.
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Old 07-06-2015, 03:33 AM
karl530 karl530 is offline
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Location: Morecambe, UK
 
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Mein Auto: E65 & E31
Thanks for the reply's everyone, I will have a look at everything that has been mentioned.

The Magus, is it easy to tell if the pump has clicked into position correctly?
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  #6  
Old 07-06-2015, 08:32 AM
The Magus The Magus is offline
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Location: Vancouver, WA
 
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Mein Auto: BMW 760Li (2008)
Look at a pic of the pump. In the image I have placed an arrow where you see a projection that has to snap into place (both sides)

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