Won't stay running in water

[tweekspark]

I recently rebuilt a rotax engine from my 2001 5524G GTX RFI Sea Doo. It has a rebuilt crankshaft, new cylinder sleeves & pistons. I added the prescribed amount of oil to the gas tank for new engine breakin. I runs great on shore with a water hose hooked up. It will not start sitting in the water. The only way I can get it to run in the water is to start it on the trailer then lower it in the water. It will only run for a couple of minutes then dies and will not restart. I pull it back out of the water and it starts up and runs fine. Throttle response is great, compression on both cylinders is 140 PSI, good spray pattern from both fuel injectors and good spark from new plugs. I inspected the exhaust system and can't find any blockage. I live in Okinawa, Japan and the local repair shops here are not cheap. I'm hoping with help from you guys, I can fix this and avoid a steep bill from a repair shop. I would greatly appreciate any help!

 

[Sportster-2001-951C-Stock]

I believe the RFI must still have the standard oil injection supply, fuel injection is direct through the cylinder head, correct? Perhaps pre-mixing oil with fuel should not be done, due to it's direct injected and there's no benefit, perhaps may cause problems?

Some ideas:

Are you confident the RV valve is installed in the correct position? If you start in water and keep the RPM high, does it still stop running?

Next step is to make note of any fault codes and measure fuel pressure using a mechanical gauge if possible. Also check battery voltage or disconnect voltage regulator after starting, this system is very sensitive to incorrect battery voltage and the regulator can malfunction, causing too much voltage.

There are many parameters to confirm on these electronic fuel injection skis.... The shop service manual covers many of them including troubleshooting flowchart.

Does the engine seem to be running out of fuel or does it seem to be receiving too much fuel? If fuel injection seems to be okay then suspect ignition malfunction, the ignition is quite voltage sensitive.

Also, it's mandatory to have a good strong battery, many complaints are traced to a weak battery. If after sitting for more than 12 hours untouched, the battery voltage should remain above 12.5 volts. If not, the battery is highly suspect.

 

[jammin777]

this sounds all too familiar. i concur with sportster, get or download the service manual and follow the diagnosis flowchart.
check the resistance of all the fuel system sensors, tps, airflow, air temp, crank position sensors,
also i will say that the tps and airflow sensors have the same plug and can easily be accidentally switched as they share the same plug type. the color codes are in the manual so check the color codes for these 2 sensors and make sure that plugs are in the right position. check fuel pressure and make sure it is within spec. if you removed the tps sensor from the throttle body, it will need to be calibrated and can only be done with a candoo pro or buds diagnostic tool. a tps sensor that needs calibrated will throw the fuel mapping off and can cause too little fuel or too much fuel.
i had a 99 gsx with new reman engine and a bunch of other stuff and would not start in water once warmed up but once started it ran great but i knew if i shut it down, it would not start again.
i spoke to someone in another forum has the same problem with a customers ski and got the problem solved with a spare mpem he had sitting on the shelf. that is the only thing i didn't try as i did not have the luxury of a spare mpem and found this out after i traded the ski for a new one.
the mpem gives the needed voltage to supply the coil the energy to produce the spark it needed to start. especially in the water. starting a ski in the water is much like trying to start a car with manual transmission in gear. it needs sufficient spark.
i also would not recommend premixing oil/fuel. as sportster said, it you will not benefit. plus premix can raise havoc with the fuel injectors. just make sure the oil pump marks are properly aligned as per manual. what rpm is the idle in the water? should be 1450 -1500 rpm. double check the rotary valve timing and clearance. the rfi are good skis but everything needs to be nearly perfect to run right. must have a good battery and cable connections. make sure the battery has sufficient cranking amps.
hope you find the problem and get it all sorted.

 

[tweekspark]

Sportster and Jammin777, thanks for the reply's. I just replaced the voltage regulator, wasn't charging the battery. Now battery voltage is over 13v while running. Waiting on a fuel supply hose I can cut to add a pressure gauge to monitor the fuel pressure. Will also run fuel without the added oil. Let you know how it works.

 

[Sportster-2001-951C-Stock]

Great, nice to hear you found an issue with the charging system. Low voltage will stop them in their tracks as well. I'm not sure if your problem will be solved, really only one way to find out for sure of course.

What is idle speed in water and on trailer? I believe for this model these should be almost the same RPM.

The fuel you remove, I advise not to use it in a vehicle that uses a catalytic converter but using it in your lawn mower should be okay I believe.

I forgot to mention before, a battery charger should not be connected to the battery UNLESS one terminal of the battery is disconnected first (usually I disconnect the negative terminal), the reason is many battery chargers will take battery voltage beyond 14.4 volts momentarily, this slight above normal voltage sometimes can damage the MPEM, thus it's risky. If this type of damage does occur, the symptom will be the MPEM will stop working completely and the 5A MPEM fuse will blow each time as soon as battery power is applied.

Good luck man, report back on your progress!

 

[Strizzo]

What was the rotary valve clearance when you rebuild the motor? Excessive rv clearance can be a cause of poor idle and stalling once warm on the carb skis.

Hopefully the charging system issue clears it up for you though.