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Stephen X20
07-12-09, 08:52 PM
I have a 2002 (Challenger) X-20 that started dying at anything over 40mph this weekend. We have had the boat for almost two months with no problems, but this weekend on an early morning run we got up about 50mph and it shut down, like someone pulled the lanyard. I turned the key off and back on and it started right up. After trying various speeds, we found out that it only shut off at almost full throttle. It would run for about 1/2 mile great and then it sounds like the engine misses just a bit and then just shuts off. I replaced the plugs and it still does the same thing. We took it out all day yesterday and stayed around 30mph and it only shut off once when the driver said he was doing 35mph. Any help would be great!

Thank you,
Stephen

rookie101
07-13-09, 10:04 PM
It sounds like you may have a problem with the low side of the fuel system. Your fuel system works like this.

The fuel is drawn from the tank by a low pressure electric lift pump which sends the fuel to an engine mounted mechanical pulse pump. From there it goes through the fuel/water separating filter, and then into the vapor separator through a needle valve controlled by a float. In the bottom of the vapor separator is a final filter attached to the bottom of a high pressure electric fuel pump that sends the fuel to the fuel rail and injectors.

If one of your low pressure fuel pumps is not working, the fuel/water separating filter is restricted, or the needle valve is sticking the vapor separator will not have enough fuel in it to keep the high pressure pump supplied when you are using lots of fuel at higher throttle settings.

You can just quickly check all your pressures on the low side. Electric lift pump 4-8 psi, engine driven pules pump 2-6 psi before and after the filter (you need to check this one with the engine running). Also if you take some tools with you, the next time it dies immediately shut the key off. Now look at the bottom of the vapor separator and you will see a drain plug. Put something under it and pull the plug to see if it is full of fuel (practice on land first so you know how much fuel should be present, and to avoid spills on the water).

You can check your fuel pump pressures on land, but wont get a good reading on the amount of fuel in the VS unless you can run it until it dies. There have been a lot of problems with the needle valve sticking, so you may want to order a new one from your dealer and just replace it if the pump pressures seem OK.

Let me know if it does not seem to be fuel related.

Aaron:cheers:

Stephen X20
06-03-10, 07:33 PM
UPDATE:

After much frustration, I finally fixed this issue. I replaced the main fuel filter and still had the same problem. After reading the service manual, I located a 2nd small in-line fuel filter and replaced it also. New plugs, two fuel filters and a tank of gas with SEAFOAM additive and it now runs like new.

WAJetboating
06-04-10, 12:44 AM
After much frustration, I finally fixed this issue. I replaced the main fuel filter and still had the same problem. After reading the service manual, I located a 2nd small in-line fuel filter and replaced it also. New plugs, two fuel filters and a tank of gas with SEAFOAM additive and it now runs like new.

As a side note: I replace both external fuel filters and all six plugs every year. I also run Seafoam in every tank, about 1/2 ounce per gallon. None of this is very expensive (compared to, say, the price of gasoline!) and it's about the cheapest insurance policy you can buy toward having a reliable boat.

I also do these things on my Rotax engines, so it's not just a "Mercury thing".