Mechanical Fuel pump causing engine knock?
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Mechanical Fuel pump causing engine knock?
So I replaced my electric fuel pump with a mechanical and now when the truck warms up I have a very noticeable knock. Also when I floor it the engine cuts out like it is not getting enough gas. When I replaced it I checked with several dealers (napa, oreilly, online) and on this forum to make absolutely sure I was getting the right pump because it was a very tight fit. Any thoughts?
Engine is a late 70's 460 from an E250 (I believe). It's had work done but not sure what and has a 775 CF carb on it.
Engine is a late 70's 460 from an E250 (I believe). It's had work done but not sure what and has a 775 CF carb on it.
Cargo Master
Joined: Apr 2009
Posts: 3,038
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From: South west Idaho
I'v never had that problem with a Ford engine , Chevy small block i have , . If you are not getting fuel too then it may be a bad pump with its own internal noise. I would test the pump first to see if that's the problem and you may be able to exchange it for another one. Sorry that's all i can think of .
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That was my assumption. It idles fine and for the most part runs like a dream unless I pound on it and when warm it gets this knock. I have fought a knock with my jeep and ended up throwing a rod out the bottom of my oil pan at 75 mph on the highway (this was not a fun experience). So knocks of this tone scare the crap out of me. I am going to get a stethoscope later today to try and verify the location. I believe if it were the pump itself it would be more of a ticking than a heavy knock? This pump is brand new btw.
Laughing Gas
Joined: Jul 2012
Posts: 1,123
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From: Southern Illinois
Brand new pumps don't mean much these days. I went and bought a brand new for my 460, installed it and tried to get it running for 3-4 hours. Exchanged it for a different one, this one works fine.
It's not uncommon for the pump to be bad for the store.
It's not uncommon for the pump to be bad for the store.
Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
A weak return spring does not mean that the engine will not run, the rod will recover it's pressure on the cam, just not as fast. So the faster the RPM's the less chance the it will deliver a good flow of fuel, and more knock. Hope it is the pump and not a rod bearing.
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Freshman User
Joined: Apr 2013
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From: Reno, NV
Jimmyrig, Do let me know when you find that knock. I got the same thing in my 75' F100 with a 360. I've replaced fuel pump, timing chain, oil pump, water pump, checked the lifters. Just wont go away. Only does it when warm, same as yours. Yours only stared after new Fuel pump though? You can feel the timing chain in there when you have pump out, is it loose? It would be one thing to eliminate. Good Luck!!
That was my assumption. It idles fine and for the most part runs like a dream unless I pound on it and when warm it gets this knock. I have fought a knock with my jeep and ended up throwing a rod out the bottom of my oil pan at 75 mph on the highway (this was not a fun experience). So knocks of this tone scare the crap out of me. I am going to get a stethoscope later today to try and verify the location. I believe if it were the pump itself it would be more of a ticking than a heavy knock? This pump is brand new btw.
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Elder User
Joined: Oct 2011
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From: Castle Rock, CO
I had a similar problem with my 74 460. I had replaced the mechanical fuel pump with a new one from Napa and all of sudden it had this very faint intermittent knock. So I replaced the fuel pump again with a new one, although it had plenty of pressure. Still knocked. After driving me nuts and listening very carefully, I thought it might be the timing chain. It turned out to be the timing chain. I don't think there was any correlation and just a coincidence but I thought it was awful odd that it happened at the same time.
Hotshot
Joined: Apr 2009
Posts: 14,333
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From: Stanley, VA
This is kinda far fetched and in the realm of "really reaching" for a cause but,
these engines use a two piece eccentric to drive the fuel pump.
The inner part of the eccentric is what actually spins, driven by the camshaft. The outer eccentric doesn't really spin. It chief function is to reduce friction and wear on the pump arm.
If the engine has been apart in the past, I can see the someone forgetting to put the outer eccentric on.
The pump would still function but I think the output might be reduced and if there is now clearance between the pump arm and eccentric, it could knock.
Like I say, this is really reaching.
This is an FE, but you can see the two piece eccentric.
these engines use a two piece eccentric to drive the fuel pump.
The inner part of the eccentric is what actually spins, driven by the camshaft. The outer eccentric doesn't really spin. It chief function is to reduce friction and wear on the pump arm.
If the engine has been apart in the past, I can see the someone forgetting to put the outer eccentric on.
The pump would still function but I think the output might be reduced and if there is now clearance between the pump arm and eccentric, it could knock.
Like I say, this is really reaching.
This is an FE, but you can see the two piece eccentric.
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doesn't sound that far fetched to me. I am leaning towards swapping back to the electric. Any recommendations for under $100? What kind of GPH and psi should I be looking for. It's a 460 with a 775 cf eddlebrock carb. My biggest complaint with the last electric one was the noise.
Hotshot
Joined: Apr 2009
Posts: 14,333
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From: Stanley, VA
That's a good possibility. Like a lot of Ford engines, it could be either single piece or two piece.
Fuel pump eccentric, 460 V8
C8SZ-6287-A single piece
D0AZ-6287-A Inner
D1AZ-6287-A Outer
Fuel pump eccentric, 460 V8
C8SZ-6287-A single piece
D0AZ-6287-A Inner
D1AZ-6287-A Outer
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I removed the mechanical fuel pump and reinstalled the electric in a more stable position with new line and filter. The knock is still there... 
There was no metal in the oil last time I changed it. How do I identify if this is a wrist pin or not? Just pull the pan and look I'm guessing?
There was no metal in the oil last time I changed it. How do I identify if this is a wrist pin or not? Just pull the pan and look I'm guessing?
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