66COUP
Member
I’ve seen similar posts across a lot of forums, but none ever seem to include the actual fix, so please bear with me here. I’ve been fighting this issue for about six months now.
I’m troubleshooting a problem on my 2001 Sea-Doo GTX RFI where the engine will initially pull to about 6850 RPM at full throttle, but if I let off the throttle and the RPM drops below about 4000 RPM, the engine will then not rev past about 4200 RPM again. When this happens, it sounds like the ignition is being cut, almost like a rev limiter or 2-step, but without popping. Sometimes the problem gets bad enough that the ski will die and will not restart, either in or out of the water. After a couple hours of cooldown, it will start right back up and run normally until the issue returns.
The strange part is that it usually has no problem running full throttle at first. I can rip it right off the trailer with no issues for at least 30 minutes, but once I let off, it may or may not go past the 4200 RPM limit again. That is why I’m leaning toward this being heat-related and possibly electronic or ignition-related.
The engine is a new reman SBT long block installed last September, along with a new rotary valve and rotary valve cover. I followed the installation and break-in instructions exactly, and the engine currently has about 9 hours on it. Rotary valve timing is exact. I also confirmed that SAE 30W oil was added for the counterbalance gear, since it arrived dry from SBT. Compression is 145 PSI on both MAG and PTO cylinders.
Fuel system checks so far:
Based on recent testing:
I also took apart the water box regulator, the one that looks like a RAVE valve, and the bellow had no holes and appeared to be in good condition.
Another thing I may not have mentioned before: the ski will not hot start in the water, but it starts fine cold. When starting, I usually have to give it a couple throttle blips. On a GTX RFI 787, are you supposed to blip the throttle when starting cold or hot, or should it start with just the button?
At this point, the ski has:
I’m troubleshooting a problem on my 2001 Sea-Doo GTX RFI where the engine will initially pull to about 6850 RPM at full throttle, but if I let off the throttle and the RPM drops below about 4000 RPM, the engine will then not rev past about 4200 RPM again. When this happens, it sounds like the ignition is being cut, almost like a rev limiter or 2-step, but without popping. Sometimes the problem gets bad enough that the ski will die and will not restart, either in or out of the water. After a couple hours of cooldown, it will start right back up and run normally until the issue returns.
The strange part is that it usually has no problem running full throttle at first. I can rip it right off the trailer with no issues for at least 30 minutes, but once I let off, it may or may not go past the 4200 RPM limit again. That is why I’m leaning toward this being heat-related and possibly electronic or ignition-related.
The engine is a new reman SBT long block installed last September, along with a new rotary valve and rotary valve cover. I followed the installation and break-in instructions exactly, and the engine currently has about 9 hours on it. Rotary valve timing is exact. I also confirmed that SAE 30W oil was added for the counterbalance gear, since it arrived dry from SBT. Compression is 145 PSI on both MAG and PTO cylinders.
Fuel system checks so far:
- Fuel pressure is consistently 58–60 PSI, including under load and at high RPM.
- New Quantum fuel pump
- New Quantum fuel pressure regulator
- New fuel filters
- Tried two different sets of injectors
- Both injector sets were cleaned and flow-tested by Fuel Injector Man
- Running NGK BR8ES solid plugs gapped at .020
- Plugs foul within about 90–120 minutes, but fresh plugs do not fix the 4200 RPM cutout
- Swapped in a different MPEM from the same year/model
- Swapped ignition coil
- Swapped plug wires and trimmed wires under the boots
- Confirmed 5 VDC at the ignition coil
- Checked coil resistance from tab 1 to tab 2 and tab 3 to tab 2
- New Bosch TPS
- New Bosch water temp sensor
- New OSD 4TEC rectifier
- TPS reset multiple times with Candoo Pro
- No Candoo fault codes
- 2 beeps on lanyard install
- New fully charged battery
- 13.9 volts at the battery at 3000 RPM
- Stator resistance checked cold and running
- Stator produces 28 VAC at idle from all legs, hot or cold
- Battery ground
- Coil ground
- MPEM ground
- All fuses
- MPEM socket grip
- MPEM connections
- Injector resistance
- TPS resistance
- Crank position sensor resistance
- Air temp sensor resistance
- Water temp sensor resistance
- Air pressure sensor resistance
- RAVE solenoid resistance
- RAVE valves move freely
- Oil pump alignment marks
- New oil lines, water lines, and vacuum lines
Based on recent testing:
- RAVE solenoid and MAG injector wires are not switched.
- TPS and APS sensor wires are not switched.
- RAVE solenoid opens when 12V is applied manually.
- All vacuum lines are new.
- I found the bulkhead fitting on the transom that leads to the RAVE solenoid was clogged, so I cleaned it out.
- Cleaning that fitting did not seem to improve the issue.
- I plan to drill small holes in the red RAVE valve caps so I can visually confirm whether the RAVE valves are opening and closing as expected.
I also took apart the water box regulator, the one that looks like a RAVE valve, and the bellow had no holes and appeared to be in good condition.
Another thing I may not have mentioned before: the ski will not hot start in the water, but it starts fine cold. When starting, I usually have to give it a couple throttle blips. On a GTX RFI 787, are you supposed to blip the throttle when starting cold or hot, or should it start with just the button?
At this point, the ski has:
- Good compression
- Steady fuel pressure
- Cleaned/tested injectors
- New or replaced fuel components and sensors
- Swapped MPEM, coil, and wires
- No fault codes
- Good charging voltage
- Correct rotary valve timing
- RAVE valves that move freely
- Oil pump confirmed working
