Defective new Fuel pump?

[CharlieB]

This one's a real kick in the head!

Pulll the coil wire, stick the carb fuel supply line in a jug and crank the engine, fuel pumps perfectly.

Using a test tank and primer bulb directly to the carb, re-arm the ignition, prime the carb, add water and stir. Engine starts and runs perfectly as long as your arm lasts squeezing the primer bulb.

Meanwhile the fuel pump gives one squirt as the engine first fires up then no more fuel till you shut off the engine and as the engine makes that final turn to a halt the fuel pump gives up one more shot.

MUST be a defective fuel pump, order up a new one and bolt it on.

And it does the same thing.

????????????????????

Check the rod, cam lobe, all the fuel lines, filters,etc.

Almost 1 inch of stroke, the rod looks perfect, slight burnishing of the ends where it contact, bore in the block feels smooth, bore measures .502, rod measures .499, feels perfect and absolutely falls out of the bore on it's own.

New pump spring tension feels good and stiff, but so does the old one, which is NOT the original, been changed once prior to my assuming maint on this boat. 96 Merc Tournament Ski aka 5.7LX

Ordered another pump, and hoping it was a defective new part.

Also taking my bathroom scale to work Monday so I can rig/have some means of measuring spring tension on these pumps.

This one has ME baffled, (and I am one of the best!)

 

[Don S]

Re: Defective new Fuel pump?

If it worked ok when you "stuck the hose in a jug of gas" then you probably have an air leak in the fuel system before the pump, or a plugged pickup in your boats fuel tank, or clogged antisiphon valve, or..........
Constantly changing good pumps isn't going to cure the problem.

 

[CharlieB]

Re: Defective new Fuel pump?

This one's a real kick in the head!

Checked the rod, cam lobe, all the fuel lines, filters,etc.

Sorry, I'm not getting off that easy,
One test tank directly to the pump, one test tank to the carb.

Both pumps perfect at CRANKING speed, BOTH pumps fail running.

Loosen the pump(s) slightly so you can see it 'wiggle' as it is stroked.

Wiggles at cranking, stops at running speed.

GOT TO be defective new part.

I'll find out Monday.

 

[pickwick03]

Re: Defective new Fuel pump?

I have had the same problem for over a year!! 7.1 liter volvo, was told the volvo fuel pumps are defective, put on serria pumps and have replaced both brands 4 - 6 times. Burns up the fuel pump 1st time out within 1 hour or sometimes the fuel pump burns up after numerous trips (30 - 40 hrs.) I have used this boat about 50 hrs. this season with no problems, last weekend it burned the low pressure pump up and I replaced it saturday nite, only to use it about 30 minutes on sunday when it burned up again!! HELP!!!!!!!

 

[CharlieB]

Re: Defective new Fuel pump?

Solved, dare I admit my own stupidity?

The new pump exhibited the same 'failure' to pump at engine speed.

Very confusing. Defective new part? Rare, very frustrating.....

Order up 2nd new pump and install

I inadvertantly 'forgot' to attach the 'overflow' line from the pump to the carb, started it up,

Viola!!!!! It works..................... til I see the line and plug it in, 50 seconds later the engine dies, no more fuel. Uhhhhhhh?

Un-plug it and re-start, runs fine and just keeps on pumping, plug in the overflow line, and the pump stops.

New carb has full time vacuum in this port, NOT just a static open line 'above' a venturi.

Re-port line to carb.

Done.

My mistake was assuming the 'new' carb was 'OK'.