Vapor Lock

[spdracr39]

Has anyone had an issue with their Tahoe vapor locking after stopping for 30 minutes to an hour? I know it is an issue and know the recommended procedure for avoiding it. I am looking for how to make it start back when we forget and just shut it down or even better a real fix so it doesn't happen at all.

 

[theBrownskull]

Re: Vapor Lock

I wonder if putting an extra blower "under the hood" on a timer to run after shutting off the engine would help remove the heat. Or putting more vents in but I do not know how that would look.

 

[spdracr39]

Re: Vapor Lock

I was thinking of a fuel vent line to screw onto the fuel rail and dump the pressure back into the tank. I was thinking that by letting the pressure out of the rail the pump would pick up fresh fuel easier. Once it gets hot under there you have to wait for the fuel lines to cool down and even with the hood wide open it takes a couple of hours sometimes. If you remember to let it idle for a few minutes and run the bilge blower for ten minutes or so it won't do it but people with CRS have problems (me) remembering to do that.

 

[vettefixer]

Re: Vapor Lock

I have recenlty experienced this vapor lock problem on my 08 q6. I found the fuel diagnostic port on the fuel rail just behind the throttle body can be pressed with a small pocket knife or finger nail (shrader valve) and another can cycle the key and the vaporized fuel can release from the line. Cycle the key untill the pump sounds like it is building pressure, the change is noticable. The boat will start right up. I am a master car technician and am convinced if the fuel return line went to the tank instead of the filter housing the vapor would be pushed to the tank with the first cycle of the key and all would be ok. The return instead goes into the housing causing the vapor to go in a loop and not escape. I will find a way to return this fuel to the tank and not the housing. When I do I will repost.

 

[spdracr39]

Re: Vapor Lock

That didn't work for me. I bought a gauge with a pressure relief and dumped the pressure back to the tank but the pump still wouldn't build pressure. The only resolution I have found is to open the engine cover when we stop and let it cool down while we swim. I can close it after the first thirty minutes. This seems to resolve the issue. I am beginning to think the problem is the regulator sticking instead of vapor lock but it is definitely related to heat soak. And yes I can also tell when it is going to start because the fuel pump sounds different.

 

[vettefixer]

Re: Vapor Lock

That didn't work for me. I bought a gauge with a pressure relief and dumped the pressure back to the tank but the pump still wouldn't build pressure. The only resolution I have found is to open the engine cover when we stop and let it cool down while we swim. I can close it after the first thirty minutes. This seems to resolve the issue. I am beginning to think the problem is the regulator sticking instead of vapor lock but it is definitely related to heat soak. And yes I can also tell when it is going to start because the fuel pump sounds different.

Maybe the only answer is a fuel cooler. One other thought, fuel pumps push better than they pull. maybe mount an additional pump between the tank and the filter housing, that will push fresh fuel all the time instead of trying to pull through the vapors.

 

[spdracr39]

Re: Vapor Lock

That is a fix that the a Merc service letter gave but it was 400.00 for the parts and it says it wont fix the issue just will make it start back. Also it speaks of a water check valve to keep hot engine water from siphoning back to the fuel cooler but mine already has that and it doesn't help. Also I don't believe this kit is available anymore although I have seen some on ebay. Your engine should already have a fuel cooler gen III which has a low pressure and high pressure pump built in. I am curious about two things if you could check and post. 1. Do you have the shield around your fuel/water separator filter? I do not. 2. what is your fuel pressure at the rail when running correctly at idle and at speed. Mine is 39 psi I have heard it is supposed to be 43-45 but I don't not have any ill effects other than this "vapor lock" problem. I have also checked for any fuel line restrictions including changing the water sep filter, checking the fuel pick-up screen and replacing the anti siphon valve temporarily with an open fitting. None of this made any difference.
Here is a copy of the service letter if you are interested.
http://www.boatfix.com/merc/Bullet/99/99_07.pdf

 

[spdracr39]

Re: Vapor Lock

Well here it is a year later and all my little tricks and cheap fixes have failed to work. I took the plunge and bought the boost pump kit and it works flawlessly. Goodbye Vapor Lock !!!

 

[smo944]

Re: Vapor Lock

Can you place a link for the boost pump kit you bought? Thanks.

 

[spdracr39]

Re: Vapor Lock

I bought it on Fleabay but the p/n is 862264A3, A4, or A7. I have pictures of the install if you are interested.

 

[spdracr39]

Re: Vapor Lock

Here is a link to the service letter. http://www.boatfix.com/merc/Bullet/99/99_07.pdf
My boat already had the check valve so all I needed was the boost pump kit.