Author Topic: MPI vapor lock  (Read 6675 times)

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Offline kahunadon72

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MPI vapor lock
« on: February 01, 2012, 11:27:30 AM »
Boat is a '97 Volanté w/ Marine Power 350 MPI.
We use the boat as normal either for cruising or skiing.  If we stop and fire up right away between skiers, there is no issue.  If we stop and drift for a bit (60-90 min - engine off), when I go to restart, the engine is very hard to fire.

I know that there is a thermostat controlled fan that will kick on when the engine compartment temp raises to a certain level, but that didn't seem to alleviate the issue.  It seems that the fan doesn't kick on until the vapor lock condition has set in.

I figured out over last season if I knew we were going to stop and drift, I would prop open the engine hatch 3" or so.  This seemed to alleviate any issues with restarting regardless of how long we drifted.

I'm in the Pacific NW where outside ambient temps in the summer are 80 degrees or less so I don't believe that to be a huge factor.

Any ideas on fixes?  My thought was to install a couple vents in the valance that the engine hatch rests on when closed but that would be just a guess.  Another thought would be to install a vent in the upper part of the engine hatch itself or maybe a combo of both.  If there was a way to get the automatic fan to kick on sooner that might be the ticket as well.
-Don
'97 Volanté

Offline RonT

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Re: MPI vapor lock
« Reply #1 on: February 02, 2012, 12:18:00 PM »
One help is to insulate the High Pres. fuel pump and line feeding it, also is the low pres pump in the front drivers side lower corner of the engine or still in the back upper left location??
Auto Air Induction: the thermostat is not adjustable & is located near the distributor & under the black plastic shroud. I have seen boats that have lost this shroud & the t-stat will not work properly. A lower t-stat is available. When the blower is running is the air discharging out the duct and blowing toward the fuel pumps?

Offline Midskier

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Re: MPI vapor lock
« Reply #2 on: February 02, 2012, 01:06:29 PM »
depending on how handy you are I have a better solution
I fought this issue in the midwest for a little while thanks to our
seasonal blends of fuel here

Dan T

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Offline kahunadon72

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Re: MPI vapor lock
« Reply #3 on: February 03, 2012, 10:15:25 AM »
Ron & Dan - thanks so much for the speedy replies.

Ron, I don't know definitively the answers to your questions - the boat is still wrapped up for the winter and the pics I have don't show detail of the fuel pumps.  As for the air flow, I don't think I lifted the hatch when it was running to determine where it was blowing.  I will take all of these as to-do items in the spring.  I've just got 1 season under my belt with this boat so I don't know her as well as I did my previous - but I will.

Dan, have you been able to find a non-ethanol station out your way?  We have very few but I wonder if non-E fuels would performs any better. 
I'll give you a ring in early spring when I get the cover off and can give better answers to these questions.

Thanks to you both!
-Don
-Don
'97 Volanté

Offline kahunadon72

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Re: MPI vapor lock
« Reply #4 on: August 14, 2016, 09:44:50 PM »
For the past several years I've propped up the engine compartment with a small 4x4 block after running & before we sit very long.
This past week on vacation it just wasn't enough.  Ambient temps in the mid 90's didn't help nor did the ethanol blended fuels.  So I am back to searching the site and came back to this thread.

Ron to answer your questions from a couple years back that I never remembered to circle back on...

"One help is to insulate the High Pres. fuel pump and line feeding it, also is the low pres pump in the front drivers side lower corner of the engine or still in the back upper left location??"   The small electric Carter fuel pump that feeds the rails (high?) is located on the driver's side lower corner.  The lines feeding it are braided - I will insulate with heat tape.  The other pump (low?) is submerged in the sump of the fuel tank.    You can see the top of the mounting bracket it in the lower right part of this pic:

"Auto Air Induction: the thermostat is not adjustable & is located near the distributor & under the black plastic shroud. I have seen boats that have lost this shroud & the t-stat will not work properly. A lower t-stat is available. When the blower is running is the air discharging out the duct and blowing toward the fuel pumps?"  I am one of the shroud-less in the world.  Would like to get a lower t-stat.  When the blower runs, yes there is air, but it is hard plumbed to discharge on the port side underneath the alternator.

-Don
'97 Volanté

Offline kahunadon72

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Re: MPI vapor lock
« Reply #5 on: August 14, 2016, 09:53:49 PM »
My attempt to insert a pic failed.  Let's try this link instead:
https://www.flickr.com/photos/53842217@N06/4976694531/
 
-Don
'97 Volanté