Fuel Tank Pressure, Leak, Fume & Vapor Control
25th February 2005
Long time ago, the fuel pressure gauge will read pressure increase once the engine is shut down. After several minutes then it will slowly reduce. Normally takes 8 hours to reduce to 30% pressure. Lately the pressure dropped immediately and considerably quickly right after shut down. The engine fuel efficiency also reduced significantly. Inspection was made to the fuel tank and fuel routes and a leak was found. After repairing the leak, the fuel pressure behavior returned to before.
After a few days the pressure drop quickly. Again there was leak. After repair the fuel pressure cannot hold pressure within the tank / fuel lines. Suspecting the repair may not be succesful.
After much thought it is suspected that the current fuel storage system does not have a pressure breather release to inlet manifold to be combusted for environmental safety.
Hence a port was made right above the fuel pump together with the fuel delivery as well as fuel return for the purpose of fuel fume pressure or water vapor release. The attempt was a failure because as soon as the engine starts the VSV for EVAP will sucks the actual fuel when full tank and wasted.
The idea is sound but the location to tap the fuel fume or water vapor was incorrect. After much thought and looking through a KE70 Chassis Manual for ideas. The correct position should be at the fuel inlet pipe near the fuel cap. That is the highest point and no fuel will ever reach that high and hence will not be sucked by VSV for EVAP when full tank. The water vapor will also accumulate there and is the best location to tap.