> My EGR doesn't seem to have a 'soft' underside like others...I guess it's
> called the diaphragm ...
> Supposedly you can check the operation of the EGR valve by pressing in this
> from underneath?? Mine is hard and appears to made of metal ...
> So, is this the original valve ( for the 305)?? Mine appears to be run by
> electronic means....( wiring from firewall side of valve)....
> What is the best way of testing the EGR valve?
Chris.. The bottom side of the stock (86SS) EGR is indeed metal. The diaphragm is internal to the EGR valve.. so if you're feeling around there, you should feel metal.. and be able to move that metal upward into the valve itself. The part number on my EGR valve is 47084737 (86SS) and is a negative backpressure type (N stamped on the top side of the valve under the part number).
The stock (86SS) EGR is vacuum operated, not electric. The vacuum applied to the valve is regulated by an ECM controlled solenoid just rear of the valve itself. So there is a vacuum line between the EGR valve and solenoid, and wires from the solenoid to the firewall harness. Maybe those are the wires you are speaking of.
To test the EGR valve / port... With the engine at idle, reach around the valve and press the movable metal part of the valve up into the valve. The engine idle RPM should decrease and become rough... and may even stall. This is the sign of a good EGR valve / EGR passage. (Use caution if the engine is at operating temperature. Use an appropriate glove to protect your hands.) Engine idle will decrease and become rough due to a weakened combustion (lean). This test does not verify the vacuum side of the valve. I suppose you could apply a vacuum source to the vacuum port of the valve to perform the same test. However, this would not verify the operation of the ECM controlled solenoid. I believe that the ECM is cognizant of the solenoid / valve / port system.. and you would get an ECM error code 53 if the system was not up to par. Haven't we all experience this one at one time or another? I know I have. :)
I think the most often cause of EGR system failure is that of a clogged EGR passage in the intake manifold. If this is the case "care should be taken to ensure that all loose particles are completely removed to prevent them from clogging the EGR valve or from being ingested into the engine." (From the Shop Manual, Section 6E1-C7) It also says to remove deposits by HAND using a small drill bit, then a screwdriver to clean the holes and chamber. "Do not use an electric drill." Also, do not use any solvents or degreaser for cleaning. Permanent damage to the valve diaphragm may result. Sand blasting is also not recommended. In severe cases, the intake manifold may need to be removed to completely clear the EGR passage back to the head.
Hope this helps. Good luck.