Fuel vapour lock (possibly)

[doofus]

I recently purchased a 2007 model Supra 22ssv which is
fitted with an INDMAR Assault 340hp motor with the ETX-Cat catalytic
convertor.

Since purchasing the boat I have been regularly experiencing problems
where the engine won't start on very hot days. I have experienced this
problem at least 6-7 times since purchasing the boat in mid December
2010.

Every time that the problem has occurred, the ambient air temperature
has been around 36-38 degrees Celsius (100-110 Fahrenheit)

In each instance where the engine will not start the circumstances
have been pretty much identical in that we have been using the boat
for wakeboarding during the morning with no problems at all, but when
we pull back into the dock to have lunch, the engine will not restart
after we have had our lunch break.

Whilst using the boat in the mornings before these incidents
everything about the engine is operating is correctly with an engine
running temperature of around 162 - 164 degrees Fahrenheit. (I forgot
to mention that the boat is also fitted with a closed water cooling
system)

The very first time this problem happened the boat started for a
brief moment but then went into "limp mode" for a few seconds and then
shut down. I tried to restart the motor but it appeared to not be
getting any fuel delivery (it did have spark). I noticed when I lifted
the engine cover that was an intense amount of radiated heat in the
actual engine bay. Because of this I lifted all engine bay and storage hatches
allowing the heat around the motor to vent out, and after doing that
we were then able to start the boat about 15 minutes later.

Since that first incident we now always lift the engine cover between
wakeboarding sets, but despite doing so we have still experienced the
exact same problem 6 more times. The circumstances have been the same
each time the problem has occurred in that we have been using the boat all morning with no problems at all, it has been an extremely hot day, and once we stop using the boat for an extended period of time to have lunch, the engine will not restart until it has completely cooled back down.

The problem occurred again on Saturday of the weekend just gone. We
had used the boat all morning with no problems at all, but it would
not restart after lunch. We had all engine and ballast hatches fully
open whilst having lunch, but it still would not start. In the end I
resorted to slowly pouring water over the engine bay area and once the
engine temp was back down to around 120 degrees I was able to get the
motor started again. (I was able to get the engine started when the
engine temp was at about 145 degrees Fahrenheit, but it again appeared
to be in sort of "limp mode" where it was running with a pronounced
miss and revs were fluctuating wildly. I only ran the engine like this
for a short time and then quickly shut it back down when realising
that it was not running correctly) I then continued to slowly pour
water over the engine, and as mentioned above, was able to restart it
properly when the engine temperature was back down around the 120
degree mark. ( I also had the engine bay blower vents on to assist in
removing the radiated heat)

I am no marine mechanic, but the problem appears to be a fuel vapour lock
or lack of fuel pressure when it gets extremely hot. In every instance where the problem has occurred we have been using the boat
during the morning with no problems at all, and it is only after
having an extended break for lunch around midday that the boat wont
restart. This problem only ever occurs on extremely hot days when the
temperature is around the 36 -39 degree Celsius mark (100 - 110
Fahrenheit). We have never experienced the problem when the
temperature has been below 35 degrees Celsius.

Has anybody else ever experienced this sort of problem, and if so, how did you fix it?

[KY Steve]

Sounds like vapor lock, its a common problem with the amount of ethanol in fuels today. You only need to pour cold water on the fuel pump itself and it should fix the problem immediately. Long term you can install a low pressure fuel pump between the tank and the current pump. I think others have also put more exhaust fans in the engine compartment.

[oward1202]

Sounds like vapor lock to me as well. I too am no mechanic but my 85 comp experiences the same type of behavior. Only on really hot days after running for a while and when the water temp is up also. Mine would not restart after running back to the dock and shutting it off to just go get the truck and back the trailer down the ramp. My simple solution was to just leave it running and rev the motor before leaving the dock to pump "new" colder fuel into the carb. I know its not the exact same setup, giving the large jump in years between the 2 boats, but as said before, the key is getting colder fuel to the engine. The previous post was correct, just pour cold water on the fuel pump. Vapor lock is nothing more than your fuel vaporizing before is able to be burned. Therefore, giving you the sense that it's not getting fuel because it's not. Hope it helps. If anyone else has more knowledge on this, please chime in because I would love to find a way to keep from dealing with this as well. It's extremely irritating as well as embarrassing when you have a great looking Supra tied up at the dock that gets looks and compliments until everyone around sees that it won't start.

Good luck.

[rludtke]

Vapor lock can affect carburated and fuel injection fuel systems. It rarely is extreme enough to affect a running engine, but will be noticed when you attempt to start a hot engine.

The root cause is high temperatures under the cowl heating the fuel in either the carb float chambers, or the fuel injection system, or the fuel supply lines, causing the fuel to vaporize. The pump can not move vapor, as gasses are compressible. Likewise, the fuel metering system can neither measure nor meter vapor, only liquid. When the engine is running, cold fuel is always entering the system, keeping the fuel temp below the vapor point of the fuel. But once shut down, the fuel heats up above the vapor point. The only recourse is to wait for the fuel temp to come down, or somehow "pass the gas" so to speak, and replace it with cold fuel.

This can be done with a carburated engine by cranking the engine with the throttle held wide open. Eventually fresh gas will enter the carb, and the engine will lite. Be ready to pull the throttle back quickly.

Fuel injection is a bit more difficult. The above method may work, but it also may not (I don't own a fuel injected boat). Many injection systems will not pass fuel unless the pressure reaches a minumum set point, and if vapor is in the system, that pressure point will not be reached, so the vapor will not be purged from the system. Cracking a fuel line while the pump is running could purge the vapor, but probably not any vapor downstream of the line break.

You could buy an extra bag of ice at the marina and set it on your fuel pump for the day.

The true root cause (the source of the heat) may need to be addressed. When I had these problems, I noticed that my under cowl temps were up, and my exhaust seemed much hotter than I thought it should be. I replaced my coolant impellor, my exhaust ran much cooler, my under cowl temps dropped, and my vapor lock problem disapeared.

[docdrs]

Rick is essentially correct , however it is vaporization in the pump itself....thus the pump cannot pump vapor, it has to be a liquid. Hence cooling the pump and returning the vapor to liquid allows the pump to work again. The solution is to have a remote or pump in tank system where the temperature is never high enough to cause vaporization inside it. I believe

[doofus]

Ok, so we all seem to agree that the problem is caused by fuel vaporisation like I thought.

I intend to try and find some way to insulate the fuel lines from the fuel tank to the fuel pump with some sort of heat resistant shielding or lagging material (a lot of high performance modified drag cars have similar problems so heat resistant lagging can be obtained readily at motor accessory shops.)

The only problem is that the damn motor is shoe-horned so tight into the engine bay you can't see diddley squat.

I have traced the lines from the fuel tank running towards the motor easily enough. I can also trace the line to a small in-line fuel filter, but after that, I just loose sight of the fuel lines because they appear to run right down the bottom of the engine near the sump area and there is just too much other stuff in the way to get to them. Hell, I can't even find the damn fuel pump itself.

I have spent a couple of hours twisting and contorting my body trying to access those fuel lines and to find the actual fuel pump without having to resort to stripping things off the motor, but I am buggered if i can do it.

This is slowly driving me nuts and frustrating me no end!!!!!

[Fman]

They (Indmar) corrected this problem by adding two fuel pumps in 2008 models. There have been many other 2006/2007 owners who have experienced this problem. Try contacting Indmar to get the second fuel pump. I never had this occur on my '08 even on 115 degree days. I believe in 2009 they went to an in-tank fuel pump which also works much better.

The fuel pump is mounted directly on the engine, this was another problem. Cooling it down with ice seems to have worked for some members to get you going. Ask JohnyB, I think he added the second fuel pump on his '07 24 SSV.