1997 BMW 850Ci Fuel Pressure Test Cost

The fuel system for all types of vehicle operates by pumping fuel from the fuel tank, sending that pressurized fuel through fuel lines, regulating the pressure, and circulating unused fuel. Since the entire system must be pressurized to function properly, when a fuel system has lost pressure it will surely fail. When this occurs, it is known as a fuel delivery issue, and the object of diagnosis focuses on finding the cause of pressure loss. Many times, locating the loss in fuel pressure is the proper procedure for diagnosing the issue, so fuel pressure testing may be conducted at one of a few locations in the fuel delivery system.

Fuel system pressure is created in the fuel tank for all vehicles. The fuel pump activates when the vehicle is in use, and constantly pumps pressurized fuel from the fuel tank, through the fuel lines. This fuel will flow through a fuel filter, though many vehicles use a fuel filter inside of the tank before the fuel is pumped. Once past the fuel filter and fuel pump, the fuel will transfer through fuel lines to the engine bay, and will take one of two paths. The fuel system may have a mechanical fuel pump to create very high pressure in the fuel system, which is the case for diesel vehicles and many performance based gasoline engines. For diesel vehicles, the fuel will first run through a fuel and water separator to remove water from the fuel. Once fuel has passed the high pressure fuel pump, it will run through a fuel pressure regulator, fuel rail or fuel injector line, and finally through fuel injectors. Most gasoline vehicles do not use the high pressure fuel pump, and will simply route pressurized fuel through a fuel pressure regulator, fuel rail, and fuel injector(s). In both cases, this provides several locations to be tested for fuel pressure testing.

Loss of fuel pressure typically results in a 'no start' or 'start and stall' condition. This means the engine will crank but not start, or the engine shuts off as soon as it is started. Also, sputtering when going uphill, pressing the accelerator, or idling is common, and when fuel pressure is only high enough to run the engine at idle, pressing the accelerator will turn the engine off. There are multiple other issues possible, but a lack of power and engine performance in general are likely.