fuel pump making a knock?

greentahoe

Seaman
Joined
Jul 30, 2005
Messages
55
Can a bad fuel pump make a knocking sound similar to a bad bearing? My 3.8 began losing power just after getting on plane a few days ago, then shortly thereafter developed a knock, sounding like a bad bearing. The timing is good, I've checked it running on fresh gas, it's not getting hot, and it has 50 lbs. of oil pressure at idle. All ignition parts are new, or very recent. Engine starts right up and idles very smoothly, but it has a very rythmic knock at idle that increases with speed. The outdrive is off the boat and the engine is ready to be lifted out, but before I take any covers off I'm going to remove the fuel pump and inspect it. <br />Any comments?
 

Reel Poor

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Jan 29, 2005
Messages
5,522
Re: fuel pump making a knock?

I'v heard mechanical fuel pumps knock on more the a few occassions. You can listen to it with a long screwdriver placed on the pump and to your ear just for proof.
 

greentahoe

Seaman
Joined
Jul 30, 2005
Messages
55
Re: fuel pump making a knock?

If the fuel pump is making this knock, will there be something obviously wrong that I can feel or see when I take it off? Such as a loose arm?
 

Reel Poor

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Re: fuel pump making a knock?

Usually thats the case. You can also operate the pump by hand (once removed) and typically hear the knock if it not an obvious problem.
 

greentahoe

Seaman
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Jul 30, 2005
Messages
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Re: fuel pump making a knock?

Thanks. I expect to take a closer look within the next couple of days. I haven't taken the motor out just yet, but it's completely disconnected. I may hook up the wiring and a garden hose and start it again to have a closer listen to the pump before I do anything else. The engine has about 100 hrs on it since a total rebuild and this is the first noise like this that I've heard. At this point I hope it is the pump, rather than a bearing. After all, there are a lot of fish that need to be caught out there!<br />On a more personal note, I recently finished 6 months of chemo for a bad case of cancer, and I've only been fishing once this year, so I want to get it going real soon. <br />Thanks for the help,<br />Jack
 

Reel Poor

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5,522
Re: fuel pump making a knock?

Glad to help Jack. Good luck with the chemo treatments, but more luck with the boat. They usually require more attention than we do. :rolleyes:
 

lilmandavis

Chief Petty Officer
Joined
Mar 9, 2006
Messages
618
Re: fuel pump making a knock?

i hear that RP!! seems like mechanics should get paid like doctors and doctors paid like us!! doctors just git-r-close and the body heals itself!! no getting it close on an engine, cause it aint gonna fix itself... :cool:
 

Scaaty

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Joined
May 31, 2004
Messages
5,180
Re: fuel pump making a knock?

I hope you have heard the Mechanic/Doctor joke. A Mechanic asks a Doctor at a party why he gets so much more money doing the same thing he does, you know, change valves, thats type of thing. Doc says try doing it with the engine still running....
 

greentahoe

Seaman
Joined
Jul 30, 2005
Messages
55
Re: fuel pump making a knock?

Reel Poor; I have the pump out. There's a little play in the operation of the pump lever. When I hold the pum in one hand and tap it with my other palm it makes the same noise I've been hearing with the engine running. Is there supposed to be any play at all in that lever when the pump is out?
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: fuel pump making a knock?

The return spring has either weakened or collapsed. There should be no play in the lever. The rap you hear is the lever rebounding each time the cam comes around to push the lever. Ask me about the brand new small block Chevy that was rebuilt because of a bearing rap only to find the problem wasn't fixed. The cause - weak fuel pump return spring!
 

greentahoe

Seaman
Joined
Jul 30, 2005
Messages
55
Re: fuel pump making a knock?

I have never been so happy to have a bad fuel pump. Thanks so much for all the help!
 
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