Does an electric fuel pump continously whir?

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Old 09-26-10, 11:51 AM
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Does an electric fuel pump continously whir?

You the key to "on" and it only whirs for a few seconds, then quits. Is that because the car "knows" that it is not running? If that is true and the fuel pump continously runs when the key is on AND running, where is the determination being made? In the computer? (and if so, how?)

Or does fuel pump relay have something to do with it?

Do all electric fuel pump cars have a fuel pump relay?, and what is it's purpose?

Can someone explain EXACTLY how the fuel pump works and all the components involved, when you just turn the key to on, and also for when you turn the key to start and then let it run?
 
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Old 09-26-10, 12:31 PM
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Depending on the vehicle. My old Chevy K1500, as you said it would charge with KO only. Then when running it would run, of course to keep the engine running, but you don't hear it because it is inside the fuel tank and insulated.
My Cummins charges with KO, but if you bump the ignition without successful start, the lift pump will run for 20 seconds to purge the system of air and circulate fuel back to the tank. With a successful start, the lift pump runs continuously. After market, frame mounted is obnoxiously loud, but if the "whirring" stops, you in trouble, man. You'll kill a $3k injector pump in short order, although the engine will keep running.
The ECM determines whether or not the pump keeps running.
 
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Old 09-26-10, 12:39 PM
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Originally Posted by chandler View Post
The ECM determines whether or not the pump keeps running.
On my car? Or on your diesel?
 
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Old 09-26-10, 01:11 PM
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Don't know, does your car have an ECM? I am assuming either the "computer" called an ECM on the Cummins determines it. When we refer to the car's "computer", in actuality there may be more than one component that controls something at the whim of the computer, and that is where the "control" lies. Interesting.
 
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Old 09-26-10, 01:23 PM
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Originally Posted by chandler View Post
Don't know, does your car have an ECM? I am assuming either the "computer" called an ECM on the Cummins determines it. When we refer to the car's "computer", in actuality there may be more than one component that controls something at the whim of the computer, and that is where the "control" lies. Interesting.
The more one understands about all the workings of the engine, the more readily one can hone in on solving problems. If you do not know the answer on certain things, for sure, you can be shooting in the dark. By knowing, you can make a long list of maybes and maybe nots, regarding symptoms you are having.
 
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Old 09-26-10, 04:15 PM
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You know that if you learn how to diagnose a short circuit in a car you gain alot of ground.
That wasn't supposed to be a pun. Unless you think it was a good one. Then it was on purpose.

Just saying it's half the battle. If you are sure that there is no fault in a senor circuit that is being indicated by a scanner tool, then you can start looking for a problem upstream and regard the sensor fault as an effect.
 
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Old 09-26-10, 05:37 PM
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Dave, to get to your original question, from the ECM to the pump there is no relay. Whoever modified mine, included an icecube relay near the pump. Dummy me, I kept replacing them due to water damage. I found out the relay was redundant, so I pulled it.
 
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Old 09-26-10, 05:59 PM
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Fuel pump

It would help to know what vehicle you are working on. On my GM when you turn the key on the fuel pump runs for a few seconds to provide fuel to start,then shuts off. Then when you start the engine the oil press switch closes a contact that starts the pump running full time.
 
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Old 09-26-10, 06:52 PM
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When you first turn the key on the computer grounds the relay to complete the circuit and the pump runs for 2 seconds. This 2 second run brings the system up to pressure as long as the lines are full. The pump will start running again when the computer sees a signal from the distributor, or crank sensor or on some vehicles an oil pressure signal. The pressure is controlled by the fuel pressure regulator. When the pressure reaches its designed setting the regulator opens and returns fuel to the tank. The pressure remains constant no matter throttle position or engine load because the regulator is controlled by engine vacuum.
 
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Old 09-26-10, 07:53 PM
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Fubar has it.

Your Dodge uses an RPM signal to the ECM to activate the Relay( It isnt a Fuel pump relay But Rather an A.S.D. relay....More on that in a moment).

Key on.. 2second prime.... ASD off..... Crank the car, any signal from distributor over 150 rpm (300 rpm at the crankshaft----Cam= 1/2 crank) and the ecm commands the ASD on.

Chandler....GM uses OIL pressure as their means of fuel pump activation, The pump feed runs thru the oil pressure sender, and when adequate oil pressure is achieved, the ckt is completed, and the pump turns on. (As an added bonus....If you lose oil pressure, the pump turns off to prevent the engine from running "DRY".) The relay belongs in the CKT . It bypasses the oil pressure switch on cold start, to prevent extended crank time.

ECMAN.... If you go back to some of your old posts, I mentioned an ASD relay. This is the guy who is responsible for feeding the Fuel pump , injectors, and ignition coil with 12V+. The pump is grounded thru the body of the car, Injectors and coil get their (-) from ECM. Memory eludes me at the moment, but this is early to mid 90's V6???? You have an S.M.E.C. controller, which Technically , according to Mother Mopar, Is NOT an ECM.
You may have a Separate "ECM" to control Trans function, which would be refferrred to as EATX (Pronounced "E-TAX"). EATX also gets his "POWER UP" feed from ASD in most cases.
 
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Old 09-27-10, 04:27 AM
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Wow, what a coincidence that this thread should show up; I'm having an intermittent problem that is apparently in the fuel pump circuit - engine likes to cut out for a second or two at odd times and gives me a "54" when I read codes - fuel pump relay or circuit. Gambled on the relay (original @ 575k miles), will have to wait and see. FWIW, even though this is a Chevy 5.7L TBI, the "run" signal is from (as near as I can tell) the distributor as per fubar's comment vice the OP sender, likely due to the Isuzu chasis (this is a Chevy W-4, aka Isuzu NPR). It'll run with the OP sender unplugged. What's bad is that I have something nagging me in the back of my brain that I chased this particular gremlin several years ago and can't for the life of me remember what that fix was at the time. I hate intermittent problems.
 
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Old 09-27-10, 07:04 AM
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Thanks fubar and unc about the distributor. I have a hunch many, many people here learned something they never knew!

On my Dodge wiring diagrams I got right from the Dodge dealership it shows a fuel pump relay and ASD. I went to Advance to take a look and see if they had something called specifically a fuel pump relay for my '92 Dodge Spirit 6-cyl, and he went and got one, and showed me. Now I guess I have to go back there and ask to see both the ASD and fuel pump relay at same time, to see if they are one in the same.

Could it be possible the inerds in an ASD relay could go bad such that current still goes to the coil, yet not to the fuel pump? Because I do have curent at the coil at all times according to my cabin-mounted voltmeter I rigged up.


Did I tell you that I took about 5 minutes to fill the tank with gas last night? There ALSO may be an association between my filling the gas tank and the bucking. I may be stirring up stuff in the tank upon hard filling. I am doing a lot of thinking and trying to tease the cause out of various things including connections, outside temperature, moisture/rain, my thumpita- thumpita- thumpita out of round tire I just replaced was shaking something loose?, and now about if adding gas to the tank (especially fast) causes the problem. Now for the last two days it has not even so much as hiccuped. ???

Now towguy -THAT is intermittent. This has been quite the mental excercise for me. I am generally pretty good at diagnosing stuff (my living depends on that), but in this case, there is so much information to tease out.
 
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