Mercruiser VST - Cool Fuel swap

[timandheidi2]

Hey guys, Looking to replace the troublesome VST system on my gen V 502 with a cool fuel system, has anyone ever done this before? Looking for some help making the swap. Thanks

 

[alldodge]

Howdy

Don't know which cool fuel you will be using so this is the basics. The VST supplies high pressure fuel to the fuel rail. The fuel which is not used is returned back to the VST. There are also other methods but as before this is the basic

The first Gen cool fuel uses two regulators, one on the fuel rail and one on the cool fuel module. High pressure fuel is supplied to the fuel rail and the fuel which is not used is returned back to the fuel filter.

Remove the fuel return line going into the VST off the fuel rail and plug.
Remove VST and fuel lines coming from fuel pump.
Under the front of the fuel rail is a regulator which has a vacuum line going from the Reg to the intake. Remove the end from the vacuum hose from the intake.
Install the cool fuel module and route lines to the fuel rail inlet.
Route new vacuum line from cool fuel Reg to Tee fitting under Plenum.
Connect upper Reg vacuum line to Tee
Install new vacuum line from remaining connection on Tee to intake vacuum port
Route new fuel line from cool fuel Reg return port to second inlet port on fuel filter.
Add new fuel line from mechanical fuel pump to cool fuel inlet port

Note parts in link below will be needed
Item 8 - 861267A1 COOLER KIT, Fuel
Item 26 - 32-861569A2 LINE ASSEMBLY Fuel
Item 27 - 25-805063 O-RING (.301 x .070) 2 each
Item 28 - 25-805970 O-RING
http://www.mercruiserparts.com/bam/subassembly/31904/2690/100
If mechanical fuel pump is also remove, run new fuel line from filter outlet to cool fuel

 

[thumpar]

The VST has a sight tube. I don't know if the cool fuel system uses one at the high pressure pump. If it does you will need to change that but if not you can plug that too.

What is wrong with the VST? Mine hasn't caused any issues. Even when the diaphragm had holes in it the system worked. To go to cool fuel you will need a lot of parts. You are probably best buying a take off unit with as much of the tubing and misc parts to do the conversion.

 

[timandheidi2]

Thanks guys, this will help alot. I purchased a takeoff. Should have all the needed parts..I was having vapor lock issues. I did run a return fuel line back to the tank. That solved the vapor lock issues. When I am at wot for more than a few minutes the engine shuts down. It always starts back up. Last time it happened I had a fuel pressure gauge on the valve. Lost fuel pressure. Was told the cool fuel system would solve both issues, and I won't need a return line.

 

[alldodge]

. Was told the cool fuel system would solve both issues, and I won't need a return line.

No.... You must have a return line, either back to the tank or the filter. The excess pressure must be bleed off otherwise your pressure will exceed specs and damage items. Routing the line back to the tank fixes the vapor lock problem, but it must go to the filter or the tank