Evaporative Emissions System: Testing and Inspection

Fig. 122 Evaporative Emission Control Diagram:

COLD ENGINE
NOTE: The coolant temperature must be below 55°C (131°F)
1. Check the vacuum lines for proper connections, Fig. 122, cracks, or blockages.

Fig. 123 Checking Vacuum To purge Control Valve:

2. Disconnect the #3 vacuum hose at the purge control diaphragm valve (on top of the charcoal canister), Fig. 123, and connect a vacuum gauge to the hose.
3. Start the engine and let it idle. No vacuum should be available. If vacuum is available, check the purge cut-off solenoid valve.

HOT ENGINE
NOTE: Engine should be at its normal operating temperature (cooling fan should cycle on and off at least once).

Fig. 124 Checking Vacuum To purge Control Valve:

1. Disconnect the #3 vacuum hose at the purge control diaphragm valve (on the charcoal canister), Fig. 124, and connect a vacuum gauge to the hose.
2. Start the engine and let it idle. Vacuum should be available. If vacuum is not available, check the purge cut-off solenoid valve.

Fig. 125 Applying Vacuum To The "PCV" Fitting Of The Purge Valve:

3. Stop the engine and connect a vacuum pump to the charcoal canister purge fitting, Fig. 125, and apply vacuum. Vacuum should hold and remain steady. If the vacuum drops, replace the charcoal canister and re-test.
4. Re-start the engine and reconnect the hose to the PCV fitting. Vacuum at the purge fitting should drop to zero. If the purge side vacuum does not drop to zero, replace the charcoal canister and re-test.
5. Remove the fuel tank filler cap.

Fig. 126 Checking Flow Through The Charcoal Canister:

6. Remove the charcoal canister purge air hose from the frame and connect it to a vacuum gauge, Fig. 126.
7. Raise the engine speed to 3500 rpm and watch the vacuum gauge. The gauge should show vacuum within about 1 minute.
a. If gauge shows vacuum, test is complete. Remove the gauge and return all hoses to normal.
b. If no vacuum is available, remove the vacuum gauge, and re-install the fuel filler cap. Go to the next step.
8. Remove the charcoal canister and check for signs of cracking, damage, or other defects.
a. If the charcoal canister is damaged in any way, replace it and re-test.
b. If the canister is OK, check the adjustment of the throttle plate in "ADJUSTMENT PROCEDURES."