Is there a way to test a fuel pump?

mtorresma

Recruit
Joined
Sep 27, 2010
Messages
1
2005 MERCURY OPTIMAX (SN1B149984) 75hp fuel injected

I am prettty sure it is the fuel pump but I will give some details :

1- Turns over but won't start.
2- Can't hear pump engage.

Is there a way to test the fuel pump to see whether or not it is functioning correctly. (or at all for that fact)

Any help is greatly appreciated. It has been a money pit year!!!

Thank-you
mtorresma
 

backyard mechanic

Petty Officer 1st Class
Joined
Jan 6, 2009
Messages
203
Re: Is there a way to test a fuel pump?

Step one to any problem on any outboard motor is get a compression test. Step two is determining the following;

Any water in the lower end?
Fuel to the carbs/injectors?
Crisp blue spark at the plug?

That said... fuel pumps work in different ways on two strokes verses 4 stroke. On a 2 stroke the oscillating pressure of the piston going back and forth sucks/pushes on the rubber diaphragm in the pump. If the diaphragm is shot/has a hole in it or has an air leak it will not work. You could also have a stuck or broken reed from over revs and worse yet, a compression issue in that one cylinder affecting the fuel pump. When there are two FP's it works the same but off the two corresponding pistons.

Over come the FP issue by assuring fuel to the cylinders. Could there be an air lock? Does the bulb squeeze up hard? Any way to get fuel into the cylinders to get it to fire up? Fittings tight? No cracks in hoses or air leaks?

On the optimax I believe the fuel is carburated and the oil injected. Could be wrong... not too familiar with the 2005 Optimax. The Black Max had a horrible problem with blowing out FP's back a number of years ago. For a few bucks, just get new FP kits and install them.

One more thing... be sure your engine isn't tilted up, fuel in the carbs is not going to suck fuel into the cylinders in a downward facing engine. Lastly, make sure the fuel enrichment valve/choke is working too.

All that in working order will make your engine sing.
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: Is there a way to test a fuel pump?

Step one to any problem on any outboard motor is get a compression test. Step two is determining the following;

Any water in the lower end?
Fuel to the carbs/injectors?
Crisp blue spark at the plug?

That said... fuel pumps work in different ways on two strokes verses 4 stroke. On a 2 stroke the oscillating pressure of the piston going back and forth sucks/pushes on the rubber diaphragm in the pump. If the diaphragm is shot/has a hole in it or has an air leak it will not work. You could also have a stuck or broken reed from over revs and worse yet, a compression issue in that one cylinder affecting the fuel pump. When there are two FP's it works the same but off the two corresponding pistons.

Over come the FP issue by assuring fuel to the cylinders. Could there be an air lock? Does the bulb squeeze up hard? Any way to get fuel into the cylinders to get it to fire up? Fittings tight? No cracks in hoses or air leaks?

On the optimax I believe the fuel is carburated and the oil injected. Could be wrong... not too familiar with the 2005 Optimax. The Black Max had a horrible problem with blowing out FP's back a number of years ago. For a few bucks, just get new FP kits and install them.

One more thing... be sure your engine isn't tilted up, fuel in the carbs is not going to suck fuel into the cylinders in a downward facing engine. Lastly, make sure the fuel enrichment valve/choke is working too.

All that in working order will make your engine sing.

sheesh
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: Is there a way to test a fuel pump?


That engine is DI(direct injected). If you cannot hear pump check the following:
1) Fuel pump harness hasnt disconnected
2) Fuel pump fuse
3) If fuse ok check fuel pump relay
4) If relay ok check for voltage at pump,if present pump has failed
 

MercGuy

Petty Officer 2nd Class
Joined
Jul 20, 2006
Messages
195
Re: Is there a way to test a fuel pump?

Step one to any problem on any outboard motor is get a compression test. Step two is determining the following;

Any water in the lower end?
Fuel to the carbs/injectors?
Crisp blue spark at the plug?

That said... fuel pumps work in different ways on two strokes verses 4 stroke. On a 2 stroke the oscillating pressure of the piston going back and forth sucks/pushes on the rubber diaphragm in the pump. If the diaphragm is shot/has a hole in it or has an air leak it will not work. You could also have a stuck or broken reed from over revs and worse yet, a compression issue in that one cylinder affecting the fuel pump. When there are two FP's it works the same but off the two corresponding pistons.

Over come the FP issue by assuring fuel to the cylinders. Could there be an air lock? Does the bulb squeeze up hard? Any way to get fuel into the cylinders to get it to fire up? Fittings tight? No cracks in hoses or air leaks?

On the optimax I believe the fuel is carburated and the oil injected. Could be wrong... not too familiar with the 2005 Optimax. The Black Max had a horrible problem with blowing out FP's back a number of years ago. For a few bucks, just get new FP kits and install them.

One more thing... be sure your engine isn't tilted up, fuel in the carbs is not going to suck fuel into the cylinders in a downward facing engine. Lastly, make sure the fuel enrichment valve/choke is working too.

All that in working order will make your engine sing.

If you read it on the internet it's got to be true, right ??
 
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