Wedge egr valve on tr7

[johnrip]

How can you tell that the egr valve is working properly?

 

[Paul Johnson]

Assuming rest of car is set about right, if the EGR is not working, then there are two possibilities. If it is stuck open you have a horrific vacuum leak, and the engine will barely idle. If it is stuck closed you have pretty harsh engine ping. Once the engine is warm, and off idle (say about 2,500 rpm), check to see that there is vacuum present at the hose to the valve. If not, fix that. If so, using a heavy glove against the heat, put your finger gently under the valve, and you should feel it moving up and down.

 

[Mark Beiser]

Why would you have a problem with pinging if the valve is stuck closed?
Just curious since there are millions of EGR valves out there that are disconnected or removed.

 

[Paul Johnson]

Mark - the egr's job is to reduce NOx, which results from high combustion temperature. The temps run higher than in pre-catalyst cars because cats function beginning at about 600F. As a result of this higher temp, NOx is produced. The egr simply recycles spent exhaust gas back into the combustion chamber; typically about 20% by volume. This means that the combustible mixture is less, which in turn means the temperature is lowered. By orifice calibration, engineers were able to maintain combustion temperature high enough to keep the catalyst functioning while still reducing or eliminating NOx. So, if the egr is disabled, you then have more combustible mixture available. Mechanics in the early days would place a stopper, usually a BB, in the vacuum line to kill the egr, and then retard the ignition timing in order to stop the pinging. Net result was zilch or worse. Hope that helps.