If the EGR system gets clogged or the valve stem seizes due to carbon clogging,
the engine may ping even when the proper fuel is used and ignition timing is
correct. One way to check the system is to run the engine at idle speed while
placing your finger on the EGR valve diaphragm, by reaching in under the housing
at the top of the valve. Have an assistant increase the throttle opening. The
valve should open and its position should modulate as the throttle is open and
closed, adjusting for each engine operating speed and throttle opening variation.
If you doubt that the system is performing properly, the best procedure is
to test the EGR valve with the engine at idle and full manifold vacuum applied
to the valve diaphragm, as follows:
- Remove the air cleaner assembly.
- Run the engine at idle.
- On 1983–84 626 models, plug the hoses of the idle compensator, thermosensor,
and reed valves. (Consult the underhood sticker showing vacuum hose routing
to identify these).
- Disconnect the vacuum sensing tube from the EGR control valve, and make
connections directly to an intake manifold tap (not to the carburetor) with
a vacuum hose.
- Connect this vacuum tube to the EGR control valve. The engine should suddenly
run very roughly or stall. If it does not, clean or replace the EGR control
valve.
- Grasp the rod of the EGR control valve or apply pressure to the spring diaphragm,
to make sure that it moves freely up and down and that there is resistance
from the actuating spring.
- Disconnect the vacuum hose from the EGR control valve and connect a vacuum
pump to the valve.
- Start the engine and run it at idle speed. Apply vacuum to the valve. Check
that the engine runs roughly or stalls when 1.6–2.4 in. Hg (40–60mm
Hg) of vacuum is applied to the valve.
- If the engine does not behave as described with the specified amount of
vacuum applied, replace the EGR control valve.
