- Accumulator:The accumulator is a pressure reservoir that has a diaphragm with a spring behind it to hold a small amount of pressurized fuel in the system to smooth out spikes in delivery and to provide residual pressure. It is generally located in the area of the fuel pump and fuel filter. It will generally have a large line connected to the fuel line on the discharge side of the fuel pump and a small vent line attached to a steel nipple on the back side (in some cases this will be vented to the atmosphere), and it is usually vented back to the fuel tank or fuel intake on the fuel pump. Disconnect this vent line and plug it so it does not leak and run the fuel pump. While the fuel pump is running, if fuel leaks out of the steel nipple, the accumulator is bad and must be replaced.
- Residual Pressure: Residual pressure is very important for proper hot restart. What you are looking for here are leaks in the system. When you shut down the engine or fuel pump, the system pressure will fall to 2.4 to 3.0 bar and stop. Pressure will slowly bleed off over time from there. If the pressure falls too quickly, look for problems in the accumulator, fuel pump check valve and fuel pressure regulator. On the Bosch KE-jet system, it is very important to have “Free Play” in the airflow sensor plate or the piston in the fuel distributor will not rest on its seal and you will have a leak down through the piston into the intake manifold.
- Fuel Pump Testing: Testing the fuel pump requires measuring the delivery volume at system pressure. This is done by attaching a hose to the return line fitting on the fuel distributor on the Bosch K-jet system, or to the return line fitting on the external fuel pressure regulator on the Bosch KE-jet system. When this hose is connected and directed into a container, run the fuel pump for 30 seconds and measure the amount of fuel in the container. You should have a minimum of 750cc to 1200cc of fuel in the container (this figure differs by model of car). If you don’t get the specified minimum amount for your car then check for problems or blockage in the fuel delivery system.