Medium and Large Leak Test (Intrusive)

NOTE: This intrusive test will only be run if the Small Leak (passive) test fails, or is inconclusive (the switch does not close)

Enabling Conditions:

40 °F to 90 °F
Engine temperature at startup within 10 °F of the ambient temperature
Fuel level less than 85%
The intrusive Medium and Large leak are conducted as follows:
De-energize the NVLD solenoid to seal the canister vent.
Activate purge shortly after closed loop. Pull the tank vacuum past the vacuum switch point (1" H2O vacuum) of the NVLD for a specific time while tracking the standard purge flow rate.
Turn purge off and determine how long it takes to decay the tank vacuum and reopen the switch. Determine the leak size from the time it took to reopen the switch. Note: Fuel level is an important determining factor.
If the switch does not close, a more aggressive purge flow will be applied to determine if it is a very large leak, missing fuel cap, problem with the NVLD device, purge flow problem, etc..

Fig 1: Natural Vacuum Leak Detection System Diagram (Figure 1)

Courtesy of DAIMLERCHRYSLER CORP.

Fig 2: Natural Vacuum Leak Detection System Diagram (Figure 2)

Courtesy of DAIMLERCHRYSLER CORP.