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

[GregF]

The VST is that vapor separator <tank> I was talking about (the $800 assembly with 2 pumps and a filter in it)
I said they like to replace that as a FRU, a lot less thinking for them.
Fewer callbacks.
If it is under warranty, don't screw with it. The warranty follows the motor serial number so I am not sure what you have to transfer.

Let them Easter egg the $800 part in there and save your money.

My neighbor was under warranty too. I was out of warranty.
Mercury is pretty good about the warranty tho.

[wed]

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.

[wrd1972]

The VST is that vapor separator <tank> I was talking about (the $800 assembly with 2 pumps and a filter in it)
I said they like to replace that as a FRU, a lot less thinking for them.
Fewer callbacks.
If it is under warranty, don't screw with it. The warranty follows the motor serial number so I am not sure what you have to transfer.

Let them Easter egg the $800 part in there and save your money.

My neighbor was under warranty too. I was out of warranty.
Mercury is pretty good about the warranty tho.

Thanks for the help.
Is this the VST:
http://www.boats.net/parts/search/Merc2 ... parts.html


According to the dealer and Mercury, it appears that the warranty has to be transferred and it can only be done up to the 2nd owner of which I am so thats gonna work out well. Does FRU = Field Replacable Unit?

[GregF]

That is the one on my motor but newer ones are oval with cooling fins and have 2 pumps in them. That is what "wed" is describing.

[GregF]

http://www.boats.net/images/diagrams/Me ... /22149.png

[wrd1972]

http://www.boats.net/images/diagrams/Me ... /22149.png

lol I think I revised my pic above when you posted your reply. I think they are the same issues.

What are the problematic parts in this assembly? The motors?

[GregF]

Yes that new style is what is in my neighbor's 115 (virtually the same as your 90)
It was still the high speed pump that was bad. Originally they were going to throw the whole fuel assembly at it but I think Mercury told them to just do the pump once they figured out they were eating it.

I am not sure why they are asking you about transferring the warranty. When they did warranty work on mine, all they did was punch the serial number into the computer and it came back "on warranty". I never really identified myself. That was my cooling problem that took several trips to fix.
The first dealer I went to slammed me with a bunch of shop charges and other crap. The second dealer just fixed it and didn't charge me a dime.
I don't go back to that first guy anymore.

By the time I had the fuel pump go bad I was several years off warranty.

[wrd1972]

Thanks for you assistance. I have been reading on-line that the VST and more specifically, these pump motors cause problems for many with these motors. This information will help me for when the warranty runs out so I can fix it myself. I will have no reservations about pulling the VST off and rebuilding it assuming the individual parts are available for it down the road.

[GregF]

I put the pump on mine in the water. It is not that big a job. Just don't drop anything in the water.

[Leisure Kraft]

The Mercury 90hp 4 cycle EFI motor starts great cold and runs strong without issue. However, once its turned off for an extended period of time, say 30 minutes, it starts fine but runs like crap. It lacks power and just falls all over itself and cant get over 3K RPM. Eventually after a few minutes of feathering the throttle, it will perk up and run fine.

I am not currently running the gas from my marina so the first step will be to burn the old gas out and try a different gas. I am also running Stabil if it matters. Remember its a EFI motor, no carbs.

Any thoughts on what is causing this?

Check the fuel line bulb, make sure that it pumps up fully and stays like that. If it deforms or loses its pressure this might be part of the problem. (Ethanol can eat away the fuel line's lining or the bulb's rigidity.) They make a class of fuel line/bulb combinations that are ethanol-ready but they're more expensive so many manufacturer's put in the cheaper version.

[wrd1972]

My boat was not equipped with a primer bulb from the factory. A guy on here with the identical boat and a local dealer confirmed this as well. Wierd but true.

[Leisure Kraft]

My boat was not equipped with a primer bulb from the factory. A guy on here with the identical boat and a local dealer confirmed this as well. Wierd but true.

Focusing on that "...feathering the throttle..." part above, I have to wonder if the throttle assembly is gummed up in there and needs to be cleaned and re-lubricated. I'm just trying to rule out the cheaper solutions before going to the fuel pump.

[wrd1972]

My boat was not equipped with a primer bulb from the factory. A guy on here with the identical boat and a local dealer confirmed this as well. Wierd but true.

Focusing on that "...feathering the throttle..." part above, I have to wonder if the throttle assembly is gummed up in there and needs to be cleaned and re-lubricated. I'm just trying to rule out the cheaper solutions before going to the fuel pump.

I appreciate the advice. It seems everyone is on the same page with it being a fuel delivery or blockage issue. The motor is still under warranty so it should not cost me anything out of pocket.

[wrd1972]

Update.
Took the boat to the dealer and they claimed the gas in the tank was full of water. Not entirely buying that but it was what they said. They also installed a fuel/water separator filter and modded the tank vent to resist water from working its way in the tank. They claim there was a vent issue for this year and model boat so that is now resolved.

Anyway the motor runs the exact same. Just off of idle, it loses power and runs like crap and till it perks up a few minutes later. I continue to believe its a fuel pump issue and I am confident the dealer never considered or diagnosed it.

My question. What is involved in removing the VST from the 90HP 4 stroke Merc outboard? I am a very experienced gear head and should be more than capable of doing this. I still have not had the time to pull the motor cover so I am just unfamiliar with boat motors in general so a few tips would be helpful.

The VST from the diagram I posted earlier, appears to be bolted to the motor with a pair of bolts and it appears it has several rubber hoses. Does this thing come off quickly and easily? I asume that once its off, it can be disassembled so the float can be inspected for sticking or other issues.

[GregF]

It comes off fairly easily. The high pressure hoses are O ring deals with a red button you push to disengage (at least on my 60). The other hose clamps are those one time crimp on deals that you need a special tool for. I replaced mine with regular clamps but the dealer will know you were in there. I am not really sure what you are looking for. A bad fuel pump looks just like a good one. I took my old one apart and still never saw why it was bad. Replacing it did fix the problem tho. I am betting it was just worn and binding up.