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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10963
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 3.0 mercruiser and the fuel pump is not pumping

Customer Question

i have a 3.0 mercruiser and the fuel pump is not pumping
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

This will take more than one reply to get your issue resolved.

Have you checked the fuel filter in the pump. Do you have a good fuel supply to the fuel pump?

If the fuel filter in the pump is clogged it won't pump fuel.

How are you determining the fuel pump isn't pumping fuel?

If you have a clogged fuel supply line it won't pump fuel. It is possible the fuel pump is bad.

Could I get the engine serial number please?

Customer: replied 1 year ago.
I had a hole in the tank and got a new one and a new pump as well the line is new to... I pulled the new pump off to look at any wear marks on the arm but only 2 little marks not wide marks... so it makes me wonder if the pump shaft off crank could be??? broken or could it be out of whack maybe could adjust?
Customer: replied 1 year ago.
Expert:  Tan replied 1 year ago.

If you put the arm on the wrong side of the cam it won't pump correctly. Is the arm on the bottom of the cam? The pump runs off the cam shaft not the crank shaft. Are you sure you have fuel up to the pump? It takes awhile for these pumps to prime as all the lines and the filter are dry of fuel?

Customer: replied 1 year ago.
sorry yes cam shaft... been a long day... I tried filling pump and supply line but no gas was getting to carb after trying for a few minutes... so when installing new pump does the push arm need to be in a certain spot?
Customer: replied 1 year ago.
I havent done anything the cam shaft everything has been outside the motor
Expert:  Tan replied 1 year ago.

No just under the cam shaft. Do this with the fuel supply line off the fuel pump crank the engine over do you feel vacuum? Then pressure on the out put side.

Is the fuel filter on the pump facing up or down? The filter should be facing up. The fuel pump p/n71327

Customer: replied 1 year ago.
filter is facing up 18-7278 sierra I do believe... I will check the pump right now
Expert:  Tan replied 1 year ago.

That's the correct fuel pump for your serial number.

Customer: replied 1 year ago.
I do have suction from the inlet side
any trick to get it going?
Expert:  Tan replied 1 year ago.

Make sure you have fuel all the way up to the fuel pump. Then make sure all your lines are tight. Leave line disconnected from the carb till you get fuel to the carburetor. You might try using an auxiliary fuel tank and a piece of hose to verify the pump is working correctly and you don't have an issue with the new tank. Since you have suction it can only be that the pump isn't getting fuel.

Customer: replied 1 year ago.
ok so I went out and tried it again its a faint suction so then I took line off tank and couldn't feel anything while turning motor over.... I recall mechanical pumps are pretty much bullet proof... this new one is acting just like the last one did so that's why im leaning twards internaly on the cam shaft??
Expert:  Tan replied 1 year ago.

It is possible, can you remove the fuel pump and look inside the hole see if the cam looks all scored up. If you aren't getting engough stroke it will be weak>

Customer: replied 1 year ago.
it doesn't look scored up at all still looks like a nice machine finish
so what would make it be a weak stroke
Customer: replied 1 year ago.
I got gas all the way to the carb had the line off and out gas came... but boat wont turn over I pull throttle and no gas goes into the bowl of carb...
Expert:  Tan replied 1 year ago.

So if you crack the fuel line at the carburetor and crank the engine do you have any fuel squirting out the fitting?

Customer: replied 1 year ago.
well I will be damned! she runs however its still is sputtering around 1300 rpm this was my original issue to begin with that's when I found a hole in the tank and a few other issues so would it be my float or needle that would cause this I did a rebuild kit but didn't re place jets because they didn't come with.... also the needle was by itself with out a small spring and pin in side it... so I put them in in hoping it would of fixed it but nope it still sputters at 1300 rpm and timing is spot on
Expert:  Tan replied 1 year ago.

What do you have the points gaped at? When the engine starts to sputter try closing the choke plate part of the way does it run better?

Customer: replied 1 year ago.
I got her going and with it all the way open it almost runs perfect... barely close it and it sputters out
Expert:  Tan replied 1 year ago.

Ok adjust the idle jet at the base of the carb till you get a good idle. The initial setting on the idle jets is 1.5 turns from lightly seated. Turn the jet in till it just does seat then back it out 1.5 turns. Once engine is warmed up fine tune the jets till you achieve the best idle. Now if the engine wants to stall on acceleration back the jet out 1/8 turn.

Customer: replied 1 year ago.
ok so I did that....I went to light seat and 1.5 turns out... it ran the same so I went out a little more and it ran worse so I went back to the 1.5 out from light seat and closed it a little it ran better but still sputtered but at a higher rpm
Customer: replied 1 year ago.
just for curious reasons... the tab used for timing.... is zero in the middle of it? and do you go by the valley or spike of the measure tab... and 4 degrees befor top dead zero? correct
Expert:  Tan replied 1 year ago.

Correct on zero then from valley to spike is worth 2 degrees. I have a spec of 8* BTDC.

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