Primer pump (fuel filter cap) is a special unit of the diesel engine, as a rule located directly on the fuel filter. The pump allows you to pump diesel fuel manually, for example in case when the system is drained (if the fuel ran out on the move) or when replacing the fuel filter. The check valve of the primer pump does not allow fuel to drain into the tank back when the car is parked, which is important for reliable engine start.
As long as it works properly, many drivers do not even know that this pump exists. But if the primer pump fails, problems start appearing.
Breakdown Symptoms
Usually the failure points of the primer pump are the check valve, membrane or housing seals, this is the reason of air ingress and/or fuel leakage. Here are some symptoms of the diesel primer pump breakdown:
- Longer engine start, particularly after a long stop;
- Unstable operation of the standalone heater;
- Thick exhaust smoke due to the mixture impoverishment;
- Visible fuel leakage;
- Running pump does not supply fuel.
You can feel haptically the primer pump does not supply fuel. When idling, you can press the pump button or lever without effort. In case the pump is operable, this effort is tangible, since the pump boosts pressure. Repairing the pump membrane is too tricky, it is easier to change the pump unit. But it is relevant to buy a pump of the right design.
Design Features
The hand pump design must ensure the proper circulation of fuel: it must be supplied from the tank to the center of the fuel filter. It goes through the inlet pipe.
Replacing the pump, sometimes you cannot be sure which pipe is the inlet or the outlet. Masuma pumps have an arrow indication at the outlet fitting.
If the pump is installed incorrectly, it does not supply fuel to the center of the filter or sucks it out. In many cars (such as diesel Toyota's) this causes problems in engine operation — lack of the fuel system pressure and corresponding ECU errors.
Some pumps (for example, Masuma MPU-2001) have a service bolt on the body, which allows you to purge air out from the system easily.
Also, when replacing the pump, keep in mind the diameter of the pipes. It must correspond to the pipe diameter of the original pump.
Masuma primer pumps are supplied with a transparent fuel strainer. This strainer does not only improve the purification of diesel fuel, but allows you to visually monitor its condition as well.
Masuma offers more than 30 models of primer pumps, which fit to dozens of popular diesel cars — mostly Japanese.