bj502

What's up with that. Once in a while I'll be idling around and the thing will quit. Or after doing some cruising and a stop at the sand bar it will start right up and away we go. After a short time it may quit. After sitting around a few it will go again and maybe not have another problem. what'sup

US1 Fountain

iTrader: (1)

I read there was a problem with the fuel pumps causing this. There is a Mercury Service bulletin on this condition.

Heres an old discussion on it.
For a couple more, do a search of 'vaporlock' in the tech section. Vaporlock

BTW, the Mercury service bulletins no longer are accessible for some reason. Used to be able to read them up until a couple months ago.

INDY27

It could also be the VST system, have it diagnosed and if you need a good deal on VST parts or the fuel pump I have both from a 160 hr. 96 502 EFI that I took off when my Procharger was installed

marinetrans

Try installing more ventilation to the inside of the motor compartment, help to lower air temperature. Check fuel line from to see if you have a small restriction (anti-si valve). BTW, no luck on any good Sidewinders.

bj502

Thanks for the info. This site is cool. Sounds like keeping that VST cool would help. Thanks for lookin, still tryin to find a set of those stabilizers.

maverick1

Just a thought - inside the VST tank ( with all the fuel plumbing on top of your motor) is your high pressure pump - there is a fine (I mean very fine) screen at the base of the pump - they have a habit of clogging up and causing lots of problems.

you might want to take a look see.

MAV

H2Xmark

that's what was wrong with one of my engines, I pulled the top off , make sure you are careful cause the oring will stick and if you strech it, it will not fit back in the groove and you have to buy a 80 dollar oring kit, the round filter screen can be cleaned with brake clean and reinstalled, you could also have a float problem are a needle and seat problem both of which are in the top of the VST tank, after cleaning no more problems on my boat at all

Revd Up

Maverick1 is right on. I had a that same problem . Drove me nuts. It was that very fine screen. No problems since.
Steve

28Eliminator

bj502, another issue with the VST tank is the ventalation of the gas fumes in it. It is equiped with a diaphram that opens up with vacumm when the engine is running, to allow the pressure to vent into the plenum. When I had this same problem, I put a fuel pressure gauge on the input line to the VST and after the boat sat for 15 minutes the pressure would increase because of heat up to 8-10psi. After starting the motor it would stay there. Now the mecanical fuel pump only puts out 4-5 psi, so it can't pump fuel against the pressure. Then you start running and the VST runs out of fuel, and your motor dies.
Now mine was a 97 and the spring was on the wrong side of the diaphram. Another service bulletin. It is in my manual that I bought 2 years ago. Apperantly they made 2 different VST top covers. Good luck!

deboatmon

As for that very fine screen in the VST tank, I always carry a spare with me. You will have great difficulty finding a replacement Saturday afternoons. Merc is REAL proud of these too. $70.00 or something like it. Just a tiny little cone shaped filter. It's not too terribly difficult to replace if you absolutely have to. The second time is a snap. The entire assembly unbolts from the rear with 9/16 or maybe 1/2 inch bolts. I would do a practice run to make sure I had the correct tools. Mark the fuel lines clearly to where you pulled them from as they will fit either position. You should probably carry a new O-ring gasket as well. You can use just a tiny bit of super glue to hold the old one in place if needed.

The VST screen is much finer than the standard Mercruiser water seperator/fuel filter. This means that if you have super fine debris ( smaller than 70 microns ), only the VST screen catches it. That is better than trashing an injector but still not nice.

After a few debris problems I installed a RACOR ( 10 micron ) filter "after" the standard Merc filter and have experienced absolutely no VST screen problems since. That is over 250hrs ago.


Good luck with your problem.