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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 10-19-2013, 06:30 PM
nedmon nedmon is offline
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Location: new canaan
 
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Mein Auto: 1998 528i, 1987 Carrera,
New fuel pump, better gas mileage

All
I just installed a new Airtex pump in my 1998 528i along with a filter. The original, at 165K miles is now a spare. The Airtex pump is a nice assembly and came with all the hose clamps and wiring. I also treated it to a new fuel filter.

The car now runs just as well as It did with the original pump but is getting a few miles better MPG.

I have no idea why this should be. Any thoughts?

Ned
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  #2  
Old 10-19-2013, 07:25 PM
mucho mucho is offline
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Location: Palmdale ,Calif
 
Join Date: Feb 2013
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Mein Auto: 1999 528i and 2012 X5
New fuel pump, better gas mileage

Just changed mine also last month 99 528I w/181k, but treated it to original fuel pump part, I've read that after market parts don't go very far, but have noticed a slight drop in MPG. Need to give some time to really see any diffrence.


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  #3  
Old 10-20-2013, 06:12 AM
AH673000 AH673000 is online now
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Location: Delaware
 
Join Date: Apr 2011
Posts: 309
Mein Auto: 1997 BMW 528i
New fuel pump, better gas mileage

Better mpg? Could be your cars computer was trying to deal with lower fuel pressure to the rack. Could have been the pump or the filter. I use Airtex parts in all my vehicles( they make many OEM parts for USA built vehicles) and have always had great service from them .




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Old 10-20-2013, 07:01 AM
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Fudman Fudman is online now
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Mein Auto: '02 530i Sport auto
Quote:
Originally Posted by nedmon View Post
The car now runs just as well as It did with the original pump but is getting a few miles better MPG.

I have no idea why this should be. Any thoughts?
In theory, there is no way a new fuel pump and/or filter should change your gas mileage unless some parameter within the fuel delivery system is changed. Since a fuel pump simply maintains fuel line pressure, changing the pump should have no impact fuel economy. More likely, your calculation of gas mileage is different from before and after. Are you using actual gallons consumed and miles driven (not the trip computer)? Are you driving the same route before and after under the same conditions? Are you comparing a large enough sample size? If not, your gas mileage calculations are just estimates. It will likely all even up over time.
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Old 10-20-2013, 10:39 AM
nedmon nedmon is offline
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Location: new canaan
 
Join Date: Jul 2006
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Mein Auto: 1998 528i, 1987 Carrera,
All,
Right now the computer shows 31.5 mpg and 65 miles travelled. I agree that it may be a measurement error but will post the MPG when I fill it next.
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Old 10-20-2013, 11:22 AM
mucho mucho is offline
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Location: Palmdale ,Calif
 
Join Date: Feb 2013
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Mein Auto: 1999 528i and 2012 X5
New fuel pump, better gas mileage

I average between 28-29 mpg, these numbers come from gallons used verses miles traveled. Computers are only a great tool, just do the real math.


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  #7  
Old 11-13-2013, 03:13 PM
nedmon nedmon is offline
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Location: new canaan
 
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Mein Auto: 1998 528i, 1987 Carrera,
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361 miles travelled, 12.5 gallons used and this is 28.9 mpg. Before changing the fuel pump, mileage was around 26/27 mpg
Ned
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