Emission Control Systems: Testing and Inspection

Fig. 15 Anti-afterburn valve:

Anti-Afterburn Valve
1. Disconnect air inlet hose from air cleaner at anti-afterburn valve, Fig. 15.
2. Start engine and run at idle.
3. Block anti-afterburn valve air inlet and ensure engine speed does not change.
4. Increase engine speed and quickly release accelerator, then ensure air is drawn into anti-afterburn valve for a few seconds after releasing accelerator.
5. If air is drawn in for more than three seconds or not drawn in at all replace anti-afterburn valve.

Servo Diaphragm
1. Connect tachometer to the engine.
2. Run engine until it reaches normal operating temperature and ensure idle speed is within specifications.
3. Shut off engine and remove air cleaner.
4. Disconnect vacuum hose between servo diaphragm and three-way solenoid valve at servo diaphragm.
5. Using suitable vacuum hose, connect inlet manifold and servo diaphragm
6. Start engine and increase engine speed to 2000 RPM with throttle.
7. Release throttle and ensure engine speed is 1000 to 1200 RPM on 626, 900 to 1100 RPM on 1982-83 B2000 except California, or 1200 to 1400 RPM on 1982-83 B2000 California or 1000 to 1200 RPM on 1984 models.
8. If engine speed is not within specifications, turn throttle opener adjusting screw in or out until specified engine speed is obtained.
9. If correct idle speed cannot be obtained through adjustment of throttle opener, replace servo diaphragm.

Air By-Pass Valve
1. Disconnect air hose between air bypass valve and hose connector at air bypass valve.
2. Ensure all other hoses and connections are in good condition.
3. Start and run at idle.
4. Place finger over air bypass valve outlet and ensure air flows out.
5. Increase engine speed and quickly release accelerator, then ensure air stops flowing for a few seconds.
6. If air stops flowing for more than three seconds or does not flow out at all, replace air bypass valve.

Dash Pot
1. Remove air cleaner and connect tachometer to engine.
2. Operate throttle lever and ensure dashpot rod extends quickly.
3. Release throttle lever and ensure throttle lever returns slowly to idle position after it has contacted dashpot rod.
4. Start engine, then slowly increase engine speed. Check engine speed when throttle lever just releases from dashpot rod.
5. If engine speed is not 1900 to 2100 RPM, adjust as follows:
a. Loosen locknut on dashpot.
b. Set engine speed to 2000 RPM with throttle lever.
c. Screw dashpot in or out until dashpot rod just contacts throttle lever.
d. Tighten locknut and ensure rod releases from throttle lever at 2000 RPM.