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1997 7.4 MPI vapor locking

R

racatk

New member
This is my first post, hope I do it right and don't offend anyone. I live in Arizona and do virtually all my boating on Lake Powell. My 1997 Chaparral 7.4 MPI has been a great boat, I bought it new. My only issue is a nagging one, since the first year and ever since, when I take the boat out it will run great for as long as I want, one, two hours or longer doesn't matter. After stopping for 30 min. or longer the boat will fire fine, idle fine, and take me out of the no wake area with no problem, however when I get out of the no wake area and throttle up it falls on it's face and then dies. Early on I thought it was the fuel pump and replace it, three or four times, and it would be fine for a summer. A few years ago I discovered that when I took off the out line of the low pressure pump there would be a release of air pressure and a small amount of fuel. Then I would reconnect the line and it would be fine, but now I am having to disconnect the line and crank the motor until I get fuel flowing out of the pump. Some times there is no fuel in the fuel line coming from the tank. I have tried removing the anti siphon valve, I tried a new anti siphon valve, all with no improvement. I have thought about installing an electric fuel pump in place of the manual low pressure pump but am not sure if that is the answer. Any help would surely be appreciated.
 
Here is Mercruisers recommendations for helping with vapor locking issues.

http://www.boatfix.com/merc/Bullet/99/99_07.pdf

Engine serial number handy?

Is the fuel filter insulator base and cap still in place along with a white Quicksilver filter #35-802893Q01?
Item #'s 4, 10, 11,
http://www.mercruiserparts.com/Show...0148.png&inbr=2705&bnbr=120&bdesc=FUEL+FILTER

Is there plenty of open room around the engine? You may need more vents near the top of the engine compartment so the heat has a place to escape while at rest.

Have you tried opening up the engine hatch just a little bit as a test to help let the heat out while at rest? In some cases opening up the engine hatch will let the engine start back up easier.

Hope you get it figured out, Good luck.:)
 
2X on the "hatch trick"!

Most engine builders now have a max engine room temperature requirement and many hull makers haven't read the new requirements or don't want to spend the money to satisfy them...the cheap test to run, next time you hit the lake, is to open the hatch when you shutdown...this will minimize any heat soaking (provided the motor isn't radiated by the sun at high noon). fire it up, close the hatch and see how the engine behaves..

If the issue is resolved, you can use the new operating procedure or fix it with another blower dedicated to heat removal...
 
Done that and it did not help at all. Thanks for the suggestion. I am going to replace the low pressure pump and put a cold wet rag on it when I am stopped. Hope that works.
 
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