The leak detection pump (LDP) is important in identifying fuel system leaks. Leaks will affect vehicle performance as well as harm the environment.
The LDP works to find leaks in a vehicle's fuel lines, with a focus on evaporative control systems (EVAP). Government regulations require leak detection testing to minimize harm to the public. Vehicle owners also benefit from these tests. Identifying and closing leaks will help maintain optimal vehicle performance. Remember that newer vehicles almost always display a "check engine" light. Leak and LDP issues are often at the heart of this warning since small leaks in hard-to-see places will do their damage without much obvious warning to the driver.
There are several key components of a leak detection pump: vacuum line from the vehicle fuel system, a sensitive diaphragm that responds to pressure changes and a solenoid interfaced with the diaphragm. The solenoid converts diaphragm responses to pre-set pressure to electrical data. This electrical data can be interpreted to accurately identify any leak presence and magnitude. A pre-set pressure gauge turns off the leak detection pump when the pump has achieved a certain pressure. The pressure is then allowed to decrease until it achieves another pre-determined value. The time it takes for pressure to drop throughout the fuel system is compared to the expected time for that system without any leaks. Larger leaks will result in a faster pressure drop. Note that the leak detection pump does not specify leak location, only its existence. If a large leak is detected via the leak detection pump, further investigation would be needed to identify leak location(s) and magnitude.
The LDP contains a solenoid and solenoid vent to calibrate pressure in the chamber containing the diaphragm. Controlled solenoid activation and deactivation is the driving force for a diaphragm pump connected to the vehicle fuel system. This is the key feature of an LDP pump. An intake pipe connects leak detection pump to the vehicle vacuum line. There are two prominent lines from the LDP to the canister and filter. The canister manifold leads to the EVAP and the filter line leads to the LDP filter, which is usually attached nearby. The EVAP canister collects and purges fuel gases. These purges are controlled by the EVAP mechanism. Note that problems with the EVAP canister could set off the “check engine light.” The filter manifold connects to an air filter. Air is drawn from the environment to pressurize the LDP. A dysfunctional air filter will let in dirt and dust that will then clog and disable the LDP mechanism, leading to further complications.
Installation and Maintenance
The complexity and awkward location of the LDP pump and related equipment means that installation and repairs are best left to a professional. Mechanical access difficulties as well as accurate pump calibration complicate LDP pump installation and proper function. Identifying leak location is the next challenge, and this may not be simple or obvious. LDP installation, repairs and other related issues are best left to experts. The money spent is well worth it in reduced risk to other vehicle components from improper installation or diagnosis of LDP-related issues.