Mercury 15hp Starting Issues

[SailnParadise]

I have a new Mercury 15hp EFI that won’t start. I ran it to the bottom of my tank which had water in it. I fouled the plugs so I cleaned them but decided to just buy new ones and keep the old ones as spares. I emptied the fuel filter as the red ring showed water. I also used an aqua sock in the tank and got fresh gas from the fuel dock. I have been trying to get it started all day. I have removed the plugs and cranked it WOT to clear it. But after installing the plugs it wont start and the plugs keep showing signs of moisture. The engine has less that 50 hours on it and it ran fine prior to the fouled plugs. Any suggestions on how to get it up and running?

[Bruce K]

I had a similar issue with my Suzi 15hp efi, I drained the filter and then followed all fuel lines and disconnected drained and flushed each part in order from filter to injectors. After priming, then cranking for a short time, the engine fired, and has run normally ever since. This is one downside of EFI, with a carby, one simply drained the float bowl.

[SailnParadise]

Originally Posted by Bruce K

I had a similar issue with my Suzi 15hp efi, I drained the filter and then followed all fuel lines and disconnected drained and flushed each part in order from filter to injectors. After priming, then cranking for a short time, the engine fired, and has run normally ever since. This is one downside of EFI, with a carby, one simply drained the float bowl.

So no carb to deal with. You just disconnected and drained all line after the filter? Did you crank it WOT after?

[Bruce K]

Originally Posted by SailnParadise

So no carb to deal with. You just disconnected and drained all line after the filter? Did you crank it WOT after?

EFI has no carburettor. I just followed the fuel lines from the filter, disconnected every junction an drained, From memory on the Suzi, there is a low pressure pump, a vapor seperator, a fuel cooler, a high pressure pump, then a line to each injector. Just disconnect each in order and drain. Throttle setting is controlled by the ECM I think, but it won't hurt to crank with WOT. Maybe cooler is after the HP pump?

[SailnParadise]

Drained all the lines, checked gaps and used my dinghy fuel tank with new gas after emptying it and still can get it started. I thought I was getting proficient in minor outboard repairs but seems not

[Tetepare]

Did you gap the plugs?

[SailnParadise]

Originally Posted by Tetepare

Did you gap the plugs?

Yea. .035 for a 2020 Mercury 15hp EFI. Even cleaned the “old” ones thoroughly and reinstalled to no avail.

[Scubaseas]

Drain the vapor separator, fuel injectors and fuel rail. I've had this happen more than once on our dive boats. Once you get water in the fuel system you need to drain it out. Easier said than done. Using alcohol or similar hydrophilic to flush the parts also helps. WD40 also works well.

[SailnParadise]

Ok. I’ll try that. For a part that is basically impossible to remove, how do I drain? Is there a way to flush it? I can unhook all the lines but a few components are difficult to remove. It’s hung off my transom at an angle on my sailboat. The clamp bolts are seized and I don’t have the time to let them sit with PB for days to remove. Otherwise I would remove it and clean it.

[SailnParadise]

I als don’t have a high pressure hose clamp. The ones up until the vapor separator are regular clamps I can undo with pliers.

[Scubaseas]

The vapor separator has a drain on it. You can try flushing out the system by:

1) Remove hose from lift pump to vapor separator. Remove spark plugs. Unplug power to the ignition coils. While cranking engine over take hose from lift pump and put into a container until only pure gasoline is pumping.

2} Drain the vapor separator tank (VST). You still have the hose from the lift pump to the VST off. Spray WD40 or pour alcohol into the VST where you took th einlet hose off. . Do not use acetone or MEK as they may damage rubber or plastic parts inside the VST. It is essential you remove any water from the VST as it holds the high pressure pump and water in the bowl will rust.

3) Remove fuel rail if possible and blow out, then spray with WD40 etc.. Ideally you would remove the injectors and drain and spray them.

4) Put everything back together. Leave plugs out and coils unplugged. Put engine to WOT and crank until you smell gas at spark plug holes.

5) Put plugs back in and hopefully you are good to go. It may run lumpy for a minute or so.

[P3sailor]

Didn't read of your responses, but if I am correct your low pressure fuel pump is inside a reservoir that holds a fair amount of fuel. That reservoir should have a small screw at the base that would allow you to drain any fuel it is holding. I have found that many marina's in the Caribbean and Mexico have fuel issues from not being filtered properly to H2O.

[SailnParadise]

Trying this now! Will take me a while.

[SailnParadise]

The retention bolt on the VST snapped so I am unable to drain. Any suggestions you n alternative methods. I have drain all other lines now.

[Scubaseas]

Originally Posted by SailnParadise

The retention bolt on the VST snapped so I am unable to drain. Any suggestions you n alternative methods. I have drain all other lines now.

If you have water in the VST it will eventaully lead to high pressure pump failure due to rust/oxidation forming. Pull the engine off, remove the VST, get a new drain boit, put it back in with antisieze or tefgel. Do it right once and be done with it.
Boats.net is good for parts/diagrams
Seloc online has service manuals.
Sadly there is no "easy" here.