Bad Fuel Or Fuel Pump Shot?

[Methodman]

Had some dramas the other day with my 2001 Mercury 115hp 4 Stroke.

The motor runs fine until you try to get a move on. Around 1500rpm it runs like its being starved of fuel, stop, start stop start ect ect without actualy shuting off. This tells me its still getting fuel but not enough to get the revs up.The 2 days days before it ran beautiful until I refilled both tanks from the same servo.

How do i tell if it is bad fuel or it is the fuel pump it self?

Any tips???

Thanks

Nath

[pelican]

Easiest check for bad fuel is just buy some fresh in another tote tank and if it runs OK it was bad fuel. Use a fresh lead and bulb or borrow a mates as that elimates another regular cause. You can sometimes smell bad fuel but with the modern concoctions the bad fuel seems to have no smell as it has little of the aromatics in it.

Bad fuel could be dirty fuel so check the easy things first like filters and for water in fuel. Then check fuel leads, bulb or connections for air leaks that are letting air in as this will cause starvation. Check the fuel bulb as they sometimes partially collapse and stop fuel flow.

Could well be electrics related from your description if it was actually dropping out rather than spluttering.

Edited January 8, 2008 by pelican

[amalfiblue]

I agree with Pelican, sounds more like you aren't getting fuel to the engine. I had a similar experience with my old motor, ended up being gunk in the filter blocking the flow.

Good luck with it

Andrew

[a boat]

HI Nath, as the other guys have mentioned, run a separate fuel tank to be certain it is not in the fuel and/or fuel tank/lines. Once you have confirmed that it is in fact a problem with the outboard you can repair the fuel pump if it is a faulty diaphragm or plunger. The other option is replace the fuel pump. Also need to check and make sure the vapour separator is functioning properly. We have seen many injectors blocked too on EFI 4-Strokes, so if you have had a bad lot of fuel run thru the engine it might pay to remove the injectors and get them service. They are automotive type injectors so many cars places can service these.

Does it muck up on the flusher becasue that makes diagonising the problem easier and in our experience with blocked injectors it usually is the case that it does not run well on the flusher either.

Look at these things and let us know what you find,

Cheers,

Huey.

[Methodman]

Thanks boys.

One thing i forgot to mention is that ive just had a 100hr service a week before.

So if it was something to do with the fuel pump you would think it would of showed up on their testing???

Ill check the filters and then run a seperate tank and lines and see if that makes it perform.

Ill keep you guys posted.

Cheers

Nath

[IWANNABROCK]

fuel pumps may not be diagnosed during service, as the diaphram can be fine one minute then just split. or if it had small crack or tear the motor isnt working hard at service due to no load out of water which means not pumping fuel hard.

[Methodman]

Yeah true.

Ill have to take it for a run using a dif tank and lines to see if it is the motor.

Hope its just an easy fix.

thanks mate

[IWANNABROCK]

no worries, if its a diaphram pump they are simple to pull apart and re-kit, just pull apart slowly and make sure everything goes back the same as when you pulled it apart.

[Geoff]

I had a similar problem which occured over a few weeks period.

On checking , the fuel filter the inlet line was blocked with some crap that came from the tank. Fixed that , thought all was OK but the problem reoccured.

Then found one of the fuel hoses was loose & it was sucking air. This was fixed , no more problem.

You may wish to check all the connections from the tank to the motor.

Geoff

[Methodman]

Thanks boys.

Sounds like its just a matter of finding the prob and then fixing it.

Ill have a look after this week and let you all know what the prob was.

thanks for your replys!!!!

Nath