Observation on cars with bad fuel punps...

[440Magnum]

Originally Posted By: Kiwi_ME
Being devil's advocate here .. in the end every brushed motor has to start from stationary and the conditions of no back EMF and therefore high current through the commutator are always going to be present. I find it difficult to accept that the conditions of low starting voltage (say 9V) does more damage to the commutator than 12.5 V or higher, and that it doesn't just start turning anyway since there is nearly zero load.


You're correct, letting the fuel pump run before cranking doesn't help the fuel pump last longer... but people perceive that it makes a difference because it does, in fact, let a weakened/failing fuel pump build enough pressure in the fuel rail to start the engine when it *is* cranked, whereas it might not be able to do so when the starter is also drawing a very large current. Once a fuel rail is pressurized the engine can start even if the fuel pump quits running during cranking. Try it some day- pull the fuel pump fuse with the engine running and you'll find that the engine can run maybe 10-15 seconds (at idle, of course) before the fuel rail pressure drops too low for the engine to run.

 

[HangFire]

Originally Posted By: another Todd
Don't most vehicles these days cut off accessory power when the key is turned to the start position. Seems to me most things shut off while cranking the engine.


Interesting, my startup procedure may soon be history, but back to the original topic... I don't think the fuel pump is one of those things that gets shut off during cranking, unless it reaches peak pressure or something.

 

[440Magnum]

Originally Posted By: HangFire
Originally Posted By: another Todd
Don't most vehicles these days cut off accessory power when the key is turned to the start position. Seems to me most things shut off while cranking the engine.


Interesting, my startup procedure may soon be history, but back to the original topic... I don't think the fuel pump is one of those things that gets shut off during cranking, unless it reaches peak pressure or something.


The fuel pump is almost always slaved to the auto-shutdown relay. The ASD relay itself is energized whenever the key is turned on, but switches back off in 2-5 seconds unless the crankshaft position sensor detects rotation. This is to shut off the fuel pump and ignition should the engine stall (or a collision be detected). Since the CPS detects rotation during cranking, the ASD and fuel pump are normally on during cranking.

Going back 50 years.... 60's Mopars do shut off all the accessories during cranking. They also apply full battery voltage to the coil side of the ballast resistor so that the coil supply voltage doesn't fall too low during cranking. All that is done mechanically with multiple contacts in the ignition switch itself in those old cars.

 

[mjoekingz28]

Originally Posted By: Merkava_4
Originally Posted By: HangFire
I've given the above explanation as to why, but with the exception of a few engineers, no one cares.


I care. Thank you for posting. Much appreciated.



Double that!

 

[Bladecutter]

Originally Posted By: 440Magnum
Originally Posted By: Corvette Owner
However, with the new "push button to start" cars, we won't be able to turn on the key, wait a few seconds, and then turn on the starter. My 2014 Impala for example.


You can on my Challenger and wifey's JGC. To start the JGC, you have to have your foot on the brake and to start the Challenger you have to have the clutch to the floor. If you don't press the pedal then pressing the starter button turns the ignition "on," runs the fuel pump, etc. but doesn't start the engine. Then press the pedal, push the button again, and the engine starts.


Yup, same deal for my old '07 Altima, and my '14 CX-5, both of which are sporting Push Button Start features.

And the Mazda does in fact shut off power to all accessories, when a Crank Engine event is occurring. My radio turns off, and then has to power back up, along with the cigarette lighter, and several other items in the car. I don't recall if it was the same in the Altima, been too long now since that car was traded in.

BC.