vapor separator tank removal and upgrade

[whitelightnin]

Hi, I am brand new so I hope I am doing this right. I have a 1995 29 foot Scaraab that i have owned for 22 years. Up to recently, I always had my work done b a marina. Now that I am retired I started to do my own work and discovered that many things were never taken care of, so here i am.
I want to remove the vst tank from my 1995 502 v8 with efi. My questions are. I know it is not a good idea to run high pressure fuel lines in the bilge, except very short ones where necessary. To avoid that can I use the mechanical pump to supply fuel to a new high pressure fuel pump mounted on the rear bulkhead along with necessary filter and then run a short high pressure line to the fuel rails. I do have a second tank connection to allow a return line back to the fuel tank. Also, where in this setup would I put a new adjustable fuel regulator with a guage. I have a defective mechanical pump now so I need to know if I need this before i order one. I know most of you are much more in tune with these issues so please speak in laymans terms as much as possible. I really appreciate any and all help.

 

[alldodge]

Howdy
502 VST should mean you have a belt driven mechanical low pressure fuel pump running off the Bravo raw water pump. Then pumps to VST

Post your serial number so we know exactly what your starting with.

I take you want to remove everything and change to something like cool fuel, or something else?

 

[whitelightnin]

Howdy
502 VST should mean you have a belt driven mechanical low pressure fuel pump running off the Bravo raw water pump. Then pumps to VST

Post your serial number so we know exactly what your starting with.

I take you want to remove everything and change to something like cool fuel, or something else?

Thanks for the reply. I do not have my serial # right with me, but you are correct as to what the present set up is. There is a mechanical pump mounted on top of the seawater pump. I have both of those removed and likely to replace both due to finding gas in the seawater pump under the fuel pump. Everything I have read indicates a faulty fuel pump and likely bearing deterioration in the seawater pump.
I would like to stay away from a cool fuel system. I can return fuel to the tank and I live in maine where our water temps are not that high, and our air temps are the same.
Can I use the mechanical pump to feed a new high pressure fuel pump mounted on the rear bulkhead just behind the location of the existing vs tank. Then from that high pressure pump thru filters to the fuel rails then return to the tank. I would like to install a new adjustable pressure regulator with a gauge but do not know where in this system to install it.

 

[whitelightnin]

Thanks for the reply. I do not have my serial # right with me, but you are correct as to what the present set up is. There is a mechanical pump mounted on top of the seawater pump. I have both of those removed and likely to replace both due to finding gas in the seawater pump under the fuel pump. Everything I have read indicates a faulty fuel pump and likely bearing deterioration in the seawater pump.
I would like to stay away from a cool fuel system. I can return fuel to the tank and I live in maine where our water temps are not that high, and our air temps are the same.
Can I use the mechanical pump to feed a new high pressure fuel pump mounted on the rear bulkhead just behind the location of the existing vs tank. Then from that high pressure pump thru filters to the fuel rails then return to the tank. I would like to install a new adjustable pressure regulator with a gauge but do not know where in this system to install it.

 

[alldodge]

My original motor was a VST setup like yours, 415 HP with VST. During repower I changed to cool fuel and now have 530 HP.

The mechanical pump was removed, cool fuel installed, fuel rail was modified so HP fuel came in from cool fuel pump and entered one side of the rail to feed injectors. The regulator in front of the rail is adjustable and was set at 40 psi. I change to MEFI 3 ECM

The return side of the rail was sent back to the tank. The rail was modified so it would fit AN fittings.

You could have same mods done, but might need to adjust for the original 37 psi

So vfar as the lines, low pressure needs no more the Type A1 and high pressure can be flexible with no issue so long as its quality connections

You can use a low pressure pump if you like

 

[whitelightnin]

did you change your ecm due to the larger horse power? What type cool fuel system did u use, mercury or aftermarket. I was hoping to stay away from any cool fuel system.

 

[alldodge]

I went to MEFI 3 due to better fuel tuning and there were more spares out there. MEFI 1 has very little adjustment for tuning fuel supply, and was the driver due to more HP build. Also changed from V-belt to serpentine but that has nothing to do with current build other then easier

There is nothing wrong with cool fuel, but my setup can be changed to Aeromotive (which would be over kill) or any HP fuel pump. The standard HP fuel pump will produce 60 to 100 psi, so the Reg does all the work

 

[whitelightnin]

I went to MEFI 3 due to better fuel tuning and there were more spares out there. MEFI 1 has very little adjustment for tuning fuel supply, and was the driver due to more HP build. Also changed from V-belt to serpentine but that has nothing to do with current build other then easier

There is nothing wrong with cool fuel, but my setup can be changed to Aeromotive (which would be over kill) or any HP fuel pump. The standard HP fuel pump will produce 60 to 100 psi, so the Reg does all the work

 

[whitelightnin]

you did not say what system you used. Mercury system are very expensive and I know there are less expensive systems out there. I am guessing from your posts so far that my idea of using the mechanical pump to feed the hp will not work. I know that is how the vst is set up, but this may be something different.

 

[alldodge]

There is nothing wrong with using a low pressure pump to feed a HP pump, I did not do that. My cool fuel module pulls fuel direct from the tank.

Think your best swap, would be get the rail modified so it will accept AN fittings. Then have new lines made or purchase

Easiest method is get double inverted flare fittings to match the VST fittings. Connect the HP side to the pump which the Reg reduces pressure to 37 psi. The return rail side should return to the tank or to the fuel filter

Pic shows cool fuel, but your return will come from the rail after the Reg as VST did if it goes back to filter

 

[alldodge]

I'm using cool fuel, but again you can use anything that will produce more then 37 psi, and then the Reg will lower it to 37 psi

 

[dubs283]

I have both of those removed and likely to replace both due to finding gas in the seawater pump under the fuel pump. Everything I have read indicates a faulty fuel pump and likely bearing deterioration in the seawater pump.

Finding fuel in the gear oil case for the pump arm/cam lobe happens way more often than not. This is not an indication of failure by any means. If you're having runnability issues and have narrowed it down to low fuel pressure/supply to the vst then maybe the pump is weak/faulty. The water pump is nla so you'll have to keep that if you just replace the mechanical fuel pump (if necessary).

I would like to stay away from a cool fuel system.

If you abate the vst and go another route with a high pressure pump this it's your best option to use mercs cool fuel set up. Can't speak for aftermarket stuff, don't deal with any high performance stuff anymore. In any case, if you decide to condemn the current set up, which you haven't mentioned is faulty other than finding fuel in the gear oil case, which again does not in any way point to failure, changing your setup will require an engine pull, plus many other steps.

 

[whitelightnin]

Finding fuel in the gear oil case for the pump arm/cam lobe happens way more often than not. This is not an indication of failure by any means. If you're having runnability issues and have narrowed it down to low fuel pressure/supply to the vst then maybe the pump is weak/faulty. The water pump is nla so you'll have to keep that if you just replace the mechanical fuel pump (if necessary).

If you abate the vst and go another route with a high pressure pump this it's your best option to use mercs cool fuel set up. Can't speak for aftermarket stuff, don't deal with any high performance stuff anymore. In any case, if you decide to condemn the current set up, which you haven't mentioned is faulty other than finding fuel in the gear oil case, which again does not in any way point to failure, changing your setup will require an engine pull, plus many other steps.

 

[whitelightnin]

Thanks for the input. I have had no issues with the vst except it is 27 years old. never been serviced or opened and from what I read, they can be very troublesome. I like to avoid trouble if possible and from my building and electrical career try to be proactive in maintaining things. My biggest concern is, will a mechanical pump supply enough fuel to a new high pressure pump to adequately supply the injectors. The mercury set up seems overly complicated for what it needs to do and i do have access to return fuel to the tank.

 

[whitelightnin]

I'm using cool fuel, but again you can use anything that will produce more then 37 psi, and then the Reg will lower it to 37 psi

 

[whitelightnin]

Thank you for all your input. I still do not know how I will go with this, but you have helped with this. The diagram you sent is good, but it has no text to know exactly what all the letters indicate. Any written text on this would be helpful. Again, thank you

 

[alldodge]

The pic was just for reference and is not like yours. Yours is below, just note all excess fuel not used must go somewhere. The VST returns to VST tank, the cool fuel returns to filter