I have installed a two tank veg oil conversion in my 300SD. And I am having problems. The veg oil is pumped by a Facet electric fuel pump that is rated at 4-7 psi through 3/8" rubber hose on hose coolant heated fuel line to a coolant heat exchanger in the engine bay. The veg oil then goes to a glowplug heated veg filter and on to a Pollack motorized 6 port valve. The diesel side still uses the stock lift pump to send the diesel through the fuel filter. The fuel filter outlet goes to the 6 port valve. The fuel outlet of the 6 port valve goes to the IP inlet. The diesel return goes to the diesel tank and the veg return is looped back to the veg supply line right before the heated veg filter. I have a boost gauge installed in a tee on the fuel delivery line right before the IP inlet, so I can measure the pressure of both the diesel and veg lines.

Here's the problem, when I switch to veg the returning diesel fuel that is still left in the system seems to over power the pressure of the veg line where the loop tees in and diesel goes backwards a little up the veg line and also fills the veg filter. The boost gauge goes from 4 psi. to beyond 20 psi. which is the highest reading on the gauge. When I disconnected the return line that feeds into the Pollack valve and let it drain into a can while the car was idling with the car switched to veg, I got 20 oz. of diesel in the can in 10 minutes, no veg oil entered the return. With the return disconnected the boost gauge read as it should, 15 psi on diesel and 4 psi on WVO. I have swiitched the banjo bleeder bolt on the fuel filter to a solid bolt. The original bolt was 25 MM long and the solid bolt is 20MM long, could this cause this problem? If anyone has any ideas I would love to hear them.

Thanks in advance,

Gilbert

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