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#4458402 - 07/13/17 03:43 PM Any benefit in priming fuel pump?
gregk24 Offline


Registered: 04/13/13
Posts: 5602
Loc: FL, USA
Title says it all. I've always turned the ignition to "run" for about two seconds before starting my cars to prime the fuel pump. Does this actually have any merit?
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#4458405 - 07/13/17 03:46 PM Re: Any benefit in priming fuel pump? [Re: gregk24]
mightymousetech Offline


Registered: 04/03/17
Posts: 1444
Loc: Ontario, Canada
Originally Posted By: gregk24
Title says it all. I've always turned the ignition to "run" for about two seconds before starting my cars to prime the fuel pump. Does this actually have any merit?


Well, BMW changed the programming on the N55 engines so the low pressure fuel pump primes as soon as you unlock the doors. They did this to try and prevent damage to the HPFP.

I have always said, it is best to turn the key to the "on" position, wait for the fuel pump to prime the system, when the check engine light goes off, start the car.


Edited by mightymousetech (07/13/17 03:48 PM)
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#4458427 - 07/13/17 04:10 PM Re: Any benefit in priming fuel pump? [Re: gregk24]
Yah-Tah-Hey Offline


Registered: 05/26/14
Posts: 3408
Loc: Columbus,Nebraska
My 04 Camry V6 starts after about two seconds of cranking so there must be fuel at the injectors. Don't think it makes any difference at all.

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#4458448 - 07/13/17 04:25 PM Re: Any benefit in priming fuel pump? [Re: gregk24]
dishdude Offline


Registered: 11/14/08
Posts: 8753
Loc: Phoenix
No.
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#4458458 - 07/13/17 04:30 PM Re: Any benefit in priming fuel pump? [Re: gregk24]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
I don't mind at all when my engine makes several revolutions before it fires off.

I'd rather it have a second or two to prime the oil pump first.

On my drag car, I wouldn't turn on the Ign/fuel pump until I saw oil pressure come up (3-4 seconds cranking)
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#4458461 - 07/13/17 04:32 PM Re: Any benefit in priming fuel pump? [Re: gregk24]
Kibitoshin Offline


Registered: 04/19/16
Posts: 693
Loc: Kaiōshinkai
Most cars don't turn on the fuel pump unless the engine is started.
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#4458486 - 07/13/17 04:43 PM Re: Any benefit in priming fuel pump? [Re: gregk24]
bioburner Offline


Registered: 09/19/16
Posts: 1418
Loc: Minnesota
my old 97 Jeep Wrangler one could hear it run as soon as you turned the key to on and if you attempted to start before it stopped you were just wasting your time and battery


Edited by bioburner (07/13/17 04:43 PM)
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#4458497 - 07/13/17 04:53 PM Re: Any benefit in priming fuel pump? [Re: gregk24]
bdcardinal Online   content


Registered: 06/03/05
Posts: 10992
Loc: Santa Barbara, CA
I do it on my Mustang. You can hear the fuel pump priming. I will turn the key to "on" and wait until fuel gauge moves up, then I hit the key.
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#4458518 - 07/13/17 05:11 PM Re: Any benefit in priming fuel pump? [Re: Kibitoshin]
Donald Offline


Registered: 03/21/04
Posts: 20457
Loc: Upstate NY
Originally Posted By: Kibitoshin
Most cars don't turn on the fuel pump unless the engine is started.


How would the car ever start? Most turn on for 10 seconds and then stay running as long as there is oil pressure.
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#4458548 - 07/13/17 05:54 PM Re: Any benefit in priming fuel pump? [Re: Kibitoshin]
CT8 Offline


Registered: 10/09/14
Posts: 10984
Loc: Idaho
Originally Posted By: Kibitoshin
Most cars don't turn on the fuel pump unless the engine is started.
O.K.
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#4458658 - 07/13/17 07:41 PM Re: Any benefit in priming fuel pump? [Re: gregk24]
raytseng Offline


Registered: 12/11/08
Posts: 2339
Loc: CA
only needed if you have a problem with your car.

To be specific this doesnt mean extra cranks. it means like even though the car cranks the first few seconds it stumbles or sputters or dies. if it cranks for 2seconds but catches perfectly you didnt change anything.

and even so this might only happen on cold start for more than 12 hours off.

my basis is when i replaced a fuel pump but did not seat an oring correctly. so the above symptoms are the real symptoms when fuel pressure is not achieved.


Edited by raytseng (07/13/17 07:43 PM)

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#4458683 - 07/13/17 07:58 PM Re: Any benefit in priming fuel pump? [Re: Donald]
Kibitoshin Offline


Registered: 04/19/16
Posts: 693
Loc: Kaiōshinkai
Originally Posted By: Donald
Originally Posted By: Kibitoshin
Most cars don't turn on the fuel pump unless the engine is started.


How would the car ever start? Most turn on for 10 seconds and then stay running as long as there is oil pressure.


I meant while the engine is starting. I've noticed on Toyota's that turn on the fuel pump as the engine cranks and runs. That's why you can't hear them prime when they is turned to the on position.
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#4459126 - 07/14/17 09:53 AM Re: Any benefit in priming fuel pump? [Re: gregk24]
Coprolite Offline


Registered: 07/03/11
Posts: 1224
Loc: Houston, TX
I don't believe this to be relevant on my 2012 F150 or 2012 BMW 335i. One is started with a button, so the computer controls the whole process and the other starts with a turn of the key that is for all intents and purposes a button. A flick of the ignition and it will start. I didn't realize this consciously until I drove my family's older Hondas. A flick of the ignition there wasn't anywhere near as productive....

I used to prime up the fuel pump on my 1967 912, but that wasn't a voluntary thing.

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#4459140 - 07/14/17 10:12 AM Re: Any benefit in priming fuel pump? [Re: Coprolite]
mightymousetech Offline


Registered: 04/03/17
Posts: 1444
Loc: Ontario, Canada
Originally Posted By: Coprolite
I don't believe this to be relevant on my 2012 F150 or 2012 BMW 335i. One is started with a button, so the computer controls the whole process and the other starts with a turn of the key that is for all intents and purposes a button. A flick of the ignition and it will start. I didn't realize this consciously until I drove my family's older Hondas. A flick of the ignition there wasn't anywhere near as productive....

I used to prime up the fuel pump on my 1967 912, but that wasn't a voluntary thing.


On the BMW, you will hear the fuel pump priming when you unlock the doors, so it is doing it without you knowing.


Edited by mightymousetech (07/14/17 10:21 AM)
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#4459193 - 07/14/17 11:36 AM Re: Any benefit in priming fuel pump? [Re: mightymousetech]
Coprolite Offline


Registered: 07/03/11
Posts: 1224
Loc: Houston, TX
Originally Posted By: mightymousetech
Originally Posted By: Coprolite
I don't believe this to be relevant on my 2012 F150 or 2012 BMW 335i. One is started with a button, so the computer controls the whole process and the other starts with a turn of the key that is for all intents and purposes a button. A flick of the ignition and it will start. I didn't realize this consciously until I drove my family's older Hondas. A flick of the ignition there wasn't anywhere near as productive....

I used to prime up the fuel pump on my 1967 912, but that wasn't a voluntary thing.


On the BMW, you will hear the fuel pump priming when you unlock the doors, so it is doing it without you knowing.


I would guess that it is linked to when it senses the key in the proximity of the car, not triggered by the actual act of unlocking. I would buy that it is linked to touching the door handle which will trigger both actions. It is also evident that it is doing it. The computer starts to boot up and all the systems get ready.

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