timeoff2fish
Recruit
- Joined
- May 17, 2009
- Messages
- 5
I have a 2004 60 HP EFI four stroke Merc that has been vapor locking for over a year. The motor has 225 hours on it, and all scheduled maintenance has been performed. The engine starts fine when cold and runs fine from idle to WOT. I live in coastal South Carolina, so the ambient air temperature can get quite hot here in the summer. The motor does not vapor lock in the winter. After I run the motor at high speeds for 20 minutes or so then shut down to fish for about 45 minutes, when I go to restart the engine will start fine initially, then idle at about 300 rpms above normal for a couple seconds, then run extremely rough and usually eventually shut down. This only happens after running and shutting down, and only around mid-day when the outside air temperature is high.
The motor does have two factory installed fuel coolers, one on the mechanical fuel pump and one at the outlet of the electric fuel pump.
If I remove the cowling for a few minutes and let the motor cool after it vapor locks, it will then crank fine and run at WOT all day long. The VST (vapor separator tank) is very hot to the touch. Water temp readings will be about 125 or so when the motor exhibits this condition.
Here are the following steps that I have taken:
1.) suspected bad gas, so I fully drained the tank and refilled it. I use the boat about once a week and usually have fresh gas in it. I use StarBrite enzyme ethanol fuel treatment. We only have E-10 gas in SC.
2.) replaced the thermostat with a new 120 degree one. The old thermostat looked pretty corroded and I thought it was not opening.
3.) replaced the water pump impeller twice over the past 50 hours as well as the cavitation plate. I did have a blown impeller (but this was after the vapor locking started last summer), and I suspected debris from the impeller or other junk in the water system as I run in shallow water, but I have repeatedly blown it out with high pressure air and WD-40. Water temp at WOT is between 120 and 123 degrees. Telltale pressure is very strong.
4.) opened up the VST and checked the fuel pump screen. No clogging.
5.) checked the fuel cooler components and found no blockage
6.) checked fuel lines were not touching the block/cylinder head and put extra insulation on the line going from the mechanical fuel pump to the VST.
7.) replaced water temperature sensor
8.) opened up the mechanical fuel pump. The diaphragm appeared to be in good shape. Again I was worried about the effects of ethanol.
9.) replaced the Racor fuel/water separator filter twice. There was no water in the bottom of the bowl.
10.) replaced fuel bulb
11.) checked and retightened all fuel hose fittings from the tank to the engine. Also replaced fuel hose attach point on outboard.
12.) I do not believe the boat (Hells Bay Boatworks 17.8 Professional flats boat) has an anti-siphon valve, but I'm calling the factory in the morning.
13.) the idle air control valve makes a louder than normal sucking sound when the motor is running rough after vapor locking, but I believe this is actually normal.
14.) After running the boat hard and prior to shutting down to fish, I will let it run at idle for a few minutes to let it cool down.
I'm about at my wits end. Any thoughts, other than hanging a Yamaha on the boat? Possibly the intake air manifold temperature or pressure sensor?
The motor does have two factory installed fuel coolers, one on the mechanical fuel pump and one at the outlet of the electric fuel pump.
If I remove the cowling for a few minutes and let the motor cool after it vapor locks, it will then crank fine and run at WOT all day long. The VST (vapor separator tank) is very hot to the touch. Water temp readings will be about 125 or so when the motor exhibits this condition.
Here are the following steps that I have taken:
1.) suspected bad gas, so I fully drained the tank and refilled it. I use the boat about once a week and usually have fresh gas in it. I use StarBrite enzyme ethanol fuel treatment. We only have E-10 gas in SC.
2.) replaced the thermostat with a new 120 degree one. The old thermostat looked pretty corroded and I thought it was not opening.
3.) replaced the water pump impeller twice over the past 50 hours as well as the cavitation plate. I did have a blown impeller (but this was after the vapor locking started last summer), and I suspected debris from the impeller or other junk in the water system as I run in shallow water, but I have repeatedly blown it out with high pressure air and WD-40. Water temp at WOT is between 120 and 123 degrees. Telltale pressure is very strong.
4.) opened up the VST and checked the fuel pump screen. No clogging.
5.) checked the fuel cooler components and found no blockage
6.) checked fuel lines were not touching the block/cylinder head and put extra insulation on the line going from the mechanical fuel pump to the VST.
7.) replaced water temperature sensor
8.) opened up the mechanical fuel pump. The diaphragm appeared to be in good shape. Again I was worried about the effects of ethanol.
9.) replaced the Racor fuel/water separator filter twice. There was no water in the bottom of the bowl.
10.) replaced fuel bulb
11.) checked and retightened all fuel hose fittings from the tank to the engine. Also replaced fuel hose attach point on outboard.
12.) I do not believe the boat (Hells Bay Boatworks 17.8 Professional flats boat) has an anti-siphon valve, but I'm calling the factory in the morning.
13.) the idle air control valve makes a louder than normal sucking sound when the motor is running rough after vapor locking, but I believe this is actually normal.
14.) After running the boat hard and prior to shutting down to fish, I will let it run at idle for a few minutes to let it cool down.
I'm about at my wits end. Any thoughts, other than hanging a Yamaha on the boat? Possibly the intake air manifold temperature or pressure sensor?
