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Old 15-11-2012, 07:37   #1
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Fuel Pumps, How Much Should They Put Out?

How do I tell if my fuel pump is moving enough fuel?
Motor wouldn't start, after having been run after a fuel line replacement.
I assumed fuel issue and changed the fuel filters, still not starting so I am checking the fuel pump. I have it removed (ODay 37 Universal Atomic 5432 mechanical fuel pump), it SEEMS to be building pressure, I cranked the starter for 5 to 10 seconds and only had a small amount of fuel come out.
Which leads to my question:
How much fuel should the pump put out?
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Old 15-11-2012, 07:55   #2
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Re: Fuel Pumps, how much SHOULD they put out?

If you have changed the fuel lines there is very high chance the engine is not starting because of air in the fuel system.
I would assume this is the cause until its absolutely proven otherwise.
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Old 15-11-2012, 08:01   #3
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Re: Fuel Pumps, how much SHOULD they put out?

--and don't forget that the pump moves much more fuel at running engine speed.
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Old 15-11-2012, 08:06   #4
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Re: Fuel Pumps, how much SHOULD they put out?

So my course of action should be to bleed the lines starting at the fuel filter nearest the tank and work towards the injectors?
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Old 15-11-2012, 08:15   #5
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Re: Fuel Pumps, how much SHOULD they put out?

Yep.

If you get really stuck. A small electric pump makes bleeding easier and will bypass problems with the lift pump (unless there is a blocked filter in the lift pump).
A simpler alternative is a fuel bulb (like on an outboard) . There is some doubt about the legality of this in the engine space, but it a simplifies bleeding and if you need to keep pumping to keep the engine going you know the lift pump is defective.

First try a careful bleed my guess is it will fix the problem.
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Old 15-11-2012, 08:37   #6
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Re: Fuel Pumps, how much SHOULD they put out?

I have had problems with mechanical pumps but not enough to switch over to an electric one. If you think your pump is your problem, take it apart and check the diaphragm along with the valves. But before you do that, you should check to see if the fuel line is plugged.

One pump that gave me trouble was the one on my Kohler 7.5kw generator. It was very intermittent so before I isolated it to the pump, I exhausted a lot of effort and money spinning my wheels. I took that pump apart and sure enough, one of the valves in the pump proper was never properly seated during its manufacture. I was able to seat the valve by finding a socket that fit over it and tapped it back into where it belonged. Runs fine ever since.

Next, one of my 454 engines had a big problem of randomly quitting without warning. I quickly isolated that to a fuel problem. Took that pump apart and sure enough, I found a valve diaphragm with a break in it. So the problem was clear, I purchased a new pump in this instance, installed it and now the engine runs reliably.

Too many years ago when I was younger, fuel pump repair kits were available for a few bucks. The kits contained two new valve and a new main diaphragm. No more! We are in a throwaway society today so I think you might be stuck buying a new pump if the one you have has failed. Pulling it apart does not guarantee an easy fix but it does help identify a failed pump.
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Old 15-11-2012, 08:41   #7
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Re: Fuel Pumps, how much SHOULD they put out?

+1 on bleeding. Most engine manuals will also have instructions on testing the pump, the usual method involves turning the engine over for a set amount of time with the fuel line going to a measuring cup, ie ten seconds should give a pint, etc.
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Old 15-11-2012, 09:12   #8
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Re: Fuel Pumps, how much SHOULD they put out?

You will find, or at least I have. The injectors tend to dislike air more than the rest of the system. This is especially true with mechanical diesels. (I know there are few electronic diesels in boats)

I would figure the injectors found the air bubbles, and are the main culprit.

When faced with that situation, I would drain (check the fuel from that filter....especially for water) the last filter before the mechanical injector pump. Then I would bleed that filter until no air came out. I would then bleed the injectors.

This method has given the best success of all other methods I have used/tried.

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Old 15-11-2012, 12:24   #9
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Re: Fuel Pumps, how much SHOULD they put out?

Uuugh! I missed reading that the engine was diesel. Just read Atomic and assumed it was the Atomic 4. My previous post is not going to help at all.
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Old 15-11-2012, 13:05   #10
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Re: Fuel Pumps, how much SHOULD they put out?

Quote:
Originally Posted by foggysail View Post
Uuugh! I missed reading that the engine was diesel. Just read Atomic and assumed it was the Atomic 4. My previous post is not going to help at all.
Ah.....don't feel bad. I had to google the engine to make sure it wasn't a gas version before I posted.

It happens to the best of us. I'm not an Atomic guy, so I was on the ropes for a few minutes.

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Old 15-11-2012, 13:18   #11
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Re: Fuel Pumps, how much SHOULD they put out?

Quote:
Originally Posted by noelex 77 View Post
Yep.

If you get really stuck. A small electric pump makes bleeding easier and will bypass problems with the lift pump (unless there is a blocked filter in the lift pump).
A simpler alternative is a fuel bulb (like on an outboard) . There is some doubt about the legality of this in the engine space, but it a simplifies bleeding and if you need to keep pumping to keep the engine going you know the lift pump is defective.

First try a careful bleed my guess is it will fix the problem.
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Old 15-11-2012, 13:28   #12
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Re: Fuel Pumps, how much SHOULD they put out?

each time the fuel lines are opened, they need to be bled.
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