BMW 1 Series Coupe Forum / 1 Series Convertible Forum (1M / tii / 135i / 128i / Coupe / Cabrio / Hatchback) (BMW E82 E88 128i 130i 135i)


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      10-30-2011, 10:14 AM   #1
mike the snake

Drives: 135i
Join Date: Sep 2011
Location: Sonoma County, CA.

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FI priming/raw fuel concerns

I hear the fuel pump run when I open the doors or trunk on my 135. I know most FI systems prime the engine for starting when the key is turned to "armed" before starting.
My old car, when hot, would sometimes have long cranks before starting unless I armed the ignition, and waited until the FI had fully primed the car, at which point it fired normally.

My concern on my 135i is that I always am going into my car for my wallet, or to load something into the trunk, and each time I hear the fuel pump run for a few seconds, and I am worried that if the car is priming itself each time, that I'm causing raw fuel to be shot into the engine in anticipation of starting, and when I Don't start the car that this raw fuel then leaks down past the rings into the oil.

Is this what is happening, or is this just the low pressure pre-pump just building pressure? Does the priming happen just when I hit the start button?

If the car IS priming every time, can this feature be disabled? I am very used to arming, and then waiting until I hear the priming pump turn off as i had to do it with my old car every time.

Thanks for any help.

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      10-30-2011, 10:31 AM   #2

Drives: 2008 135i 6MT
Join Date: Jul 2010
Location: Bury St Edmunds UK

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2008 135i  [3.00]
The low pressure pump you hear when you unlock the car is priming the high pressure fuel pump. This ensures that the HPFP is not suffring small cavitations upon start up. It is not allowing the injectors to prime or squirt fuel in to the engine.
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      10-30-2011, 03:37 PM   #3
Major General
roundel335's Avatar

Drives: 13 335i Sedan, 16 228i Cabrio
Join Date: Apr 2010
Location: Leland, NC

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^+1 - Also happens when you open the door if you haven't locked it and the car sits for awhile.

2013 F30 335i M-Sport 8AT/MPE/MPPK/JB+, 2016 228i M-Sport Cabrio 8AT
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      10-31-2011, 08:33 AM   #4
First Lieutenant

Drives: 135i DCT
Join Date: Jun 2011
Location: Melbourne, Australia

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No fuel is being injected anywhere when you hear that noise - just pressurising the system ready for starting.

These engines are direct injection so the only time fuel enters the cylinder is at the precise time in the combustion cycle and not a millisecond earlier!
BMW - 135i DCT
Audi - Q5 3.0TDI
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