Any benefit in priming fuel pump?

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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?
 
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.
 
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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)
 
Most cars don't turn on the fuel pump unless the engine is started.
 
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
 
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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.
 
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.
 
Originally Posted By: Kibitoshin
Most cars don't turn on the fuel pump unless the engine is started.
O.K.
 
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.
 
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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.
 
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.
 
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.
 
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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.
 
Originally Posted By: Coprolite
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.


So that would mean every time you walk near the car with the key in your pocket the fuel pump will prime itself? I could see it being triggered by unlocking the doors, but not being near it. I must walk past at least two of my vehicles with keys in my pocket a dozen times a day, never entering or driving them.
 
I'm pretty sure my GTI just primes the pump when I open a door. Can't be sure if that door includes the trunk, but it certainly does it when opening the driver door.
 
Originally Posted By: demarpaint
Originally Posted By: Coprolite
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.


So that would mean every time you walk near the car with the key in your pocket the fuel pump will prime itself? I could see it being triggered by unlocking the doors, but not being near it. I must walk past at least two of my vehicles with keys in my pocket a dozen times a day, never entering or driving them.


I don't lock my car at home when it is in the garage. I guess you responded to my post before I finished elaborating on it...touching the door handle is what triggers a response to being near it, from what I can recall.
 
Originally Posted By: Coprolite


I don't lock my car at home when it is in the garage. I guess you responded to my post before I finished elaborating on it...touching the door handle is what triggers a response to being near it, from what I can recall.


That makes more sense, touching a handle or actually unlocking the vehicle, thanks!
 
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