MERC 260 bad fuel pump??

[yuioutta]

I recently purchased a merc 260 and finally got it all rigged on my boat. The fuel system was plumbed almost exactly like they showed on Diamond Marine's website under EFI fuel system 101. The only exception being I have 2 tanks and had to put a tee in before the water seperator. What happens is when I turn on the key the fuel pressure will rise to 39 psi within a few seconds, then it will drop to about 37 psi at idle. Seems normal so far, then after about 60 seconds the pressure will start to fall until it reaches 12 psi at 90 seconds and then to motor dies. It will not restart at this point unless I press in the key about 5 times to get some fuel in the motor. Then it will only fire for a couple of seconds until that fuel is burned off. If I let it sit for about a half hour until what I think is when the fuel pump cools off, then it will pump back up and start this process all over.

My guess is bad fuel pump. Anybody got any ideas?

Thanks, Shawn

[mer]

is both tanks full...would'nt be sucking air out of one of the tanks would it...which tank did you send the return to fuel to...are both tanks connected by a low tank fuel line ..

[yuioutta]

Both tanks are full. The return is going back to water seperator. No the tanks are not connected by a low tank fuel line. This is in a Laveycraft tunnel hull.The tanks are in the outer parts of the hull. No way to run a line down low. There is fuel available at the inlet side of the pump. Supply lines are -8 areoquip with all inlet fittings also -8 xrp and pickups are 1/2 brass tubes soldered to fittings at the tanks. The filter and bracket are new supplied by Diamond Marine and the passages have been machined out to .406. I cannot find anywhere for air to enter system.

Thanks for the ideas.

[johnnyracer]

Pump , Voltage to the pump , Something lose in the line or filter or tank getting pulled into the pump supply side, no vent system. Does the pump change in sound as in slow down . Take the line lose on the pressure side and flow it into a container to see if its a volume problem with the pump. Then put a line on the suction side into a completely seperate fuel supply and see if something changes.

Just brain storming. Johnny

[yuioutta]

Was running this on a fresh battery charge and then to make sure I had a charger hooked up and voltage was 14.6. All lines, fittings and filters are new and free of obstructions. I checked the tanks out really good to make sure there was no foreign material. I checked the volume at the return line and it was still ok, just no pressure. The pump sound does change but not like it slows down, it sounds like it frees up, like when you first turn it on until it builds pressure when it cold. Then when it warms up it sounds like it frees up again. I will try giving the pump a different supply from a gas can just to see if that changes anything. Thanks for the ideas!

[Jay Smith]

If your running the normal OEM Mercury Bosch fuel pump normally supplied on 260's they are VERY delicate , if you install it with its normal holder and apply too much pressure to the "C" clamp it will squeeze the pump housing causing the impellar to rub the housing and burn it up.

I would test the system with an external tank or fuel source feeding the pump ( in other words COMPLETELY by pass your in boat tanks ) and see if its really the pump or the fuel supply source ( your tanks, fuel lines, filter , routing , etc.. ) COMPLETELY by passing your supply should point you in a direction of the issue causing the problem..

Just my thoughts.
Jay

[Raceman]

You might also try pinching the bypass hose on the engine shut to see if the pressure comes up and stays constant.;)

[yuioutta]

If your running the normal OEM Mercury Bosch fuel pump normally supplied on 260's they are VERY delicate , if you install it with its normal holder and apply too much pressure to the "C" clamp it will squeeze the pump housing causing the impellar to rub the housing and burn it up.

I would test the system with an external tank or fuel source feeding the pump ( in other words COMPLETELY by pass your in boat tanks ) and see if its really the pump or the fuel supply source ( your tanks, fuel lines, filter , routing , etc.. ) COMPLETELY by passing your supply should point you in a direction of the issue causing the problem..

Just my thoughts.
Jay

It is the OEM Mercury Bosch pump and I recieved it already installed in the c clamp so I had no prior control over how tight it was.:mad: I will try running this with an external fuel sorce and completely bypass the boat fuel system though. Thanks!

[yuioutta]

You might also try pinching the bypass hose on the engine shut to see if the pressure comes up and stays constant.;)

Great idea! I had already tried it though. Thanks.

[pyro]

If there's no leaks, and your pressure doesn't go sky-high when you pinch off the return line, then you have a bad fuel pump.

[YELLOWSS]

sounds like a air leak in the return line, but pinching it would show that. usually when a pump goes south it is done!!!!look for a kink where you put a tee in the fule lines. any kink in the fuel supply system would cause it. or if it sucking air through the tee and not fuel!!!!!! disconnect the tee, and se what happens, or pinch off the one side. you could always put a shut off valve there if that is the problem...

roy

[1BadAction]

those hard clamps are rough on pumps, snag one of the rubber cushioned ones from Brucato.

[yuioutta]

There is alot of great ideas on here. I thank you all. Unfortunately we are in the process of getting hit with the craziest snow storm this winter. So my testing is going to have to wait until another day:( .

[yuioutta]

I substituted a different fuel pump and it all works good now. At least in the driveway anyway.:cool:

THANKS to all who offered help and ideas!!

[sms]

I substituted a different fuel pump and it all works good now. At least in the driveway anyway.:cool:

THANKS to all who offered help and ideas!!

Glad you found the problem. How's it run?
Pics?

Note also I see it's on a Lavey, check carefully where the rear seat frame goes when you lower it into place. On mine the fuel line had to be routed carefully to avoid being pinched due to where the tank pickup location is.