1974 Mercruiser 5.8 mechanical fuel pump problems

Bill kubiak · Oct 28, 2011

I just had the fuel pump rebuilt and on the bench clamped into a vise it works perfect, but when I install it on the motor it does not work. Is it possible to install it incorrectly?

Are there any diagrams of what makes the operating arm go up and down

Bt Doctur · Oct 28, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

sounds like a Ford motor, arm is usually operated by the off-set lobe of the camshaft

Bill kubiak · Oct 29, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

It is a ford block and the pump has a long arm on it, is it possible to install it incorrectly.

Bondo · Oct 29, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

Bill kubiak said:
It is a ford block and the pump has a long arm on it, is it possible to install it incorrectly.

Ayuh,... Anything is Possible, but it's unlikely....

Is there fuel available from the tank to pump,..??
If there's a restriction upstream, it can't pump what can't get to it...

frank246 · Oct 29, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

The lever can actual catch above the excenter ring (on the front of the cam sprocket), if you are not sure... unbolt and reinstall with a spoon up wise movement to be sure the lever is under the exenter...it can happen, had it once on my 302!
It can take some time starting untill the pump catches up when there is air in the line.
good luck!

Bill kubiak · Oct 29, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

Can anyone tell me the correct model number pump for this engine 1974 Mercruiser 5.8

The reason I am asking is that with the pump on the motor when it cranks over it produces very little suction on the inlet port
On the bench in a vise when I push the lever all the way down it produces great suction
I am thinking I may have the wrong pump or the arm on my pump is bent incorrectly just a tad
The difference on the bench between some suction and great suction is about a quarter of an inch more travel moving it by hand all the way down

If that is so I am thinking to bend it a tad in my vise waddyathink?

Pete104 · Oct 29, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

I think your lobe on the front side of the cam gear is shot! It doesn't really mean that the arm would show any signs of being worn out. If you can move it & have good vaccum, then it ain't moving enough when installed.
Try Bond-o's suggestion with a remote tank. You may find a cracked pick-up in the tank!

Bill kubiak · Oct 30, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

I thought the canshaft was cast from one piece, are you suggesting the fuel pump lobe is replaceabler????????

I plan the blow all the fuel lines from the pickup inside the tank to the line going thru all the lines and the filter and into the fuel pump by pressurizing the tank via it's vent line and at the opposite end have it flow thru a clear plastic hose into a clean container, if that is clear I can go from there

I have the pump lever in a vise with some heavy pressure on the bend, it is been sitting that way over the weekend, if I can move it even a 1/16 of an inch it should increase the movement and the suction

I cannot do much this weekend with all the wind and rain

Bill kubiak · Oct 30, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

How much freeplay should this pump have before the diaphargm moves?

Bill kubiak · Oct 30, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

The number on my AC pump flange is 40960 can anyone tell me what that pump was originally for?? or if it is in fact the correct pump for this motor.

I am starting to think there might have been a pump swap somewhere down the line

joewithaboat · Oct 30, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

here is what the eccentric looks like, they can were out.
http://www.jegs.com/i/Comp-Cams/249/235/10002/-1?parentProductId=1061698

I think i recall one time installing one as a kid on a 302 where the arm went above the eccentric and bolted up but would not work. Its been almost 30 years so.... maybe you did the same?

They can be a bear to get on if the eccentric is on the peak... rotate the motor a bit, easier on the heel. It will need to be compressed with the bolts as you snug it up, as i recall.

As far as rebuilding the fuel pump.. Ive only done that a few times on a mechanical pump and don't recall much about it other than old diaphragms were ruptured, kits have new springs etc.

Pete104 · Oct 30, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

I googled "ac fuel pump 40960" & got to a menu that had CorrectCraft in it. Go open it up & see what you can learn. There is a few there!

Bill kubiak · Nov 2, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

Please, is there anyone that can give me the correct part number for the fuel pump for a 1974 mercruiser 5.8 (ford Block)

Bondo · Nov 2, 2011

Re: 1974 Mercruiser 5.8 mechanical fuel pump problems

Bill kubiak said:
Please, is there anyone that can give me the correct part number for the fuel pump for a 1974 mercruiser 5.8 (ford Block)

Ayuh,... Accordin' to the listings here at iboats,...
All the V8 Fords run This pump, right here...

1974 Mercruiser 5.8 mechanical fuel pump problems

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