One last problem with my Mercury 90hp 4 cycle EFI outboard.

[wrd1972]

I am not really sure what you are looking for.

The local dealer is going to send a mechanic down to drive it. If I were to pull the VST off, I would be looking at the float for binding or some kind of corrosion that could prevent it from properly operating the low pressure pump as designed. I am still reluctant to pull the VST because the motor still has warranty and I want thdealerer to absorb the cost. BTW I make my living doing failure analysis on complex mechanics and electronics and definitely know what to look for if something is not working as intended.

[GregF]

BTW I make my living doing failure analysis on complex mechanics and electronics and definitely know what to look for if something is not working as intended.

I did too, (30 years at IBM) I am just saying, a bad pump is not going to look bad and that is what it sounds like you have.
You are right having the dealer do this. They can afford to be throwing $200-800 parts at it.
I was off warranty when mine went bad so I had to have a good idea what I was dealing with before I bought the parts. (hence hooking up a pressure gauge)
I still let a Mercury service bulletin talk me into throwing a $80 fuel pressure regulator at it that didn't fix anything before I got a pump..

[pote]

That assembly is called the fuel supply module in the service manual. It also includes a cooling coil, fuel pressure regulator and a float switch... much like the float switch in a carburetor. The volume in this small tank is like the float bowl on a carburetor with the high pressure fuel pump immersed in the fuel. The lift pump fills the tank until the float switch cuts if off at the correct fuel level. The float switch went bad in mine and the module was over-filled. The excess fuel will go to the crankcase and gives a high oil level on the dipstick. The gas fumes will travel up the vent line to the air filter and destroy the foam filter. That was what clued them about the bad switch.

Warranty covered the repair with no questions asked.

This caught my eye - when you say you tilted the motor out, then back into the water, it ran better/normal? Maybe the float switch it sticking. Do your alarms work? havent run a Merc EFI, but the older carb models retarded the RPM if the temp got too high, as I recall. Tilting the motor might have dislodged something in your water pump?

[GregF]

Did you see this thread

viewtopic.php?f=2&t=9856

It might be worth pulling the plug in the bottom of the VST and see what comes out.

[wrd1972]

Did you see this thread

viewtopic.php?f=2&t=9856

It might be worth pulling the plug in the bottom of the VST and see what comes out.

Thanks for that link. I am going to the boat this afternoon to check the plugs next and then I am going to look at pulling the VST for inspection of the strainer. I will respond back with results ASAP.

[GregF]

I would start by taking out the drain plug (#19 in that picture up thread) and seeing what you get in a cup.
If it looks like contaminated gas, you have a clue.

[wrd1972]

Greg F.
Thanks for all of your help.

Do you know if the intake (or any other significant part) has to be removed in order to remove the VST?

[GregF]

Based on my 60, you just remove the hoses, an electrical connector, the top 2 screws (through the shock mounts) and it lifts out of the bottom shock mount.
The high pressure hoses to injector rail have a quick disconnect (red tab you push in, on mine).
I would drain it into a cup before I did all of that to see what comes out.
If there is no sign of contaminated gas, you are probably not going to fix anything by taking it apart.

[wrd1972]

Update. It appears to be fixed.

The Mechanic went to the boat which is slipped at a local lake and drove and experienced the problem. He then replaced the FSM (Fuel Supply Module also referred to as VST) float that operated the pump that provides fuel to the FSM. He also replaced the FSM reference rubber hose that appears to provide pressure to the fuel pressure regulator. I know these two items were replaced because he left the older parts on the boat and also explained that this would be covered by the Mercury warranty.

He then told me it right spot on. I then went and ran it rather hard and it never bogged one single time.

I still find it unfortunate that the dealer first charged me nearly $200 for a fuel/water evaluation and blamed the problem on water in the gas. I had no faith at all, that bad gas was going to be the problem and I even suggested to the mechanic up front, to look at the float in the FSM when it initially went in for service two weeks ago. In the future, I will insist that they dont do this fuel/water analysis based on this experience or take the the boat with the tank bone dry.

Regardless, I am going to have to swallow this slightly bitter $200 pill to keep the peace with the dealer and just be happy that the motor appears to be fixed and running perfectly. I also have the float instruction sheet that he left in the box and this appears to be a very simple install for when this might happen again in the future.

I also found this interesting service bulletin on line:
http://marinepartsexpress.com/Merc_Prod ... 009-09.pdf
http://marinepartsexpress.com/Merc_Prod ... 008-10.pdf

Thanks to all who chimed in on the thread.

[GregF]

If he left you the whole assembly you know you have at least 2 good parts of the 3 major ones in there.
(2 fuel pumps and a regulator)
I have been asking around and I am hearing more stories of these things simply being plugged up with bad gas and the crap that entails. (3 more guys). I just talked to one tonight on the river.

I would carefully take it apart, look inside and hope for gunk. You may find a good cleaning of the tank and the pump strainer gets you a good "hot" spare. It might almost be worth swapping it back to be sure it is good, then drain whichever one you keep for the spare, put it in a bag and store it in a safe place.

[wrd1972]

Let me clarify.
There were only two parts replaced to resolve the problem. The FSM float and the reference rubber hose. All of the other internal FSM parts IE: pumps and regulator are still original as far as I know.

[Leisure Kraft]

Update. It appears to be fixed.

The Mechanic went to the boat which is slipped at a local lake and drove and experienced the problem. He then replaced the FSM (Fuel Supply Module also referred to as VST) float that operated the pump that provides fuel to the FSM. He also replaced the FSM reference rubber hose that appears to provide pressure to the fuel pressure regulator. I know these two items were replaced because he left the older parts on the boat and also explained that this would be covered by the Mercury warranty.

...

Thanks to all who chimed in on the thread.

Congratulations on getting that fixed!

Come to think of it, maybe a hose failure (alone) on that reference line could also cause a problem like that; the FSM wouldn't be able to properly judge when it's supposed to turn back on the low-pressure pump.

[GregF]

The regulator is on the high pressure pump. I am not sure what the hose does. Mine doesn't even have a hose on that port but it is the same regulator. That is just the atmospheric pressure reference.

[Leisure Kraft]

The regulator is on the high pressure pump. I am not sure what the hose does. Mine doesn't even have a hose on that port but it is the same regulator. That is just the atmospheric pressure reference.

It sounds like an "op amp" in electronics.

In theory it would provide a reference amount of pressure on one side of a mechanism so that the pressure may be measured on the opposite side as the difference. There would be one or two diaphragms in there and they'd be attached to something that regulates the flow of fuel in this case. When the pressure changes the diaphragm moves, opens/closes the valve more/less and there you go. But if the reference side isn't working then the whole thing fails.

[wrd1972]

Without seeing the hose on the motor, I cant really comment on its actual purpose.

I did disect the float and it operates off of a magnetic principal. The "bobber" has a fixed magnet ring that one it raises to its upper most position in the float body, it opens the circuit. Once the bobber drops, the circuit closes and the pump turns on to fill the FSM.

Either the magnet has lost some of its magnatism, or the encapsulated switching mechanism has simply failed and cant respond to the magnet. I tried a continuity test with a multimeter and it was never able to go closed circuit.