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I had a curiosity of what in the insides look like of a typical smog era V8 back-pressure EGR valve.
took it a part and also cutoff the pintle tube.
If you look at the end of the pintle, there are two small holes across from each other.
The backpressure of the exhaust goes through these small pintle holes and up the pintle tube , and then along with engine vacuum, the pintle is lifted off the seat to allow exhaust into the intake smog tubes, lowering the temperature of the combustion chamber and reducing NOX levels.
These small holes are easy to get plugged up, and EGR not work.
There's some year CSM that says to clean EGR, remove it from the engine and whack sharply with a mallet until it works freely.
Being as I've put a bb in the vacuum line on most every GM EGR car I've owned, never had to whack one. Now, the Fords with their back pressure EGR, you have to keep those functional...
I de-EGR-ed my Ford van a couple years ago, but it was carbonned up anyways. I have taken a modern Explorer's EGR valve out and stepped on it to break it loose.
To my knowledge, GM used at least 3 different types of EGR valves on Olds engines. Positive back pressure, negative back pressure, and simple vacuum controlled, aka ported. The latter 2 can be checked for operation by attaching a vacuum source to the EGR valve. The positive backpressure unit will just sit there if you do that as it does not respond to the simple vacuum test. Many good, positive type EGR valves have been replaced by people thinking the diaphragm was bad doing a vacuum check. This is why it's important to know which type you have originally if you replace them. If you are not using it, then who cares.
Not sure about aftermarket, but the ACDelco brand valves have a P (positive) or an N (negative) stamped on the EGR head (usually the last character stamped on the unit numbering system, found on bottom right). No P or N stamping usually means it's a ported unit.
To my knowledge, GM used at least 3 different types of EGR valves on Olds engines. Positive back pressure, negative back pressure, and simple vacuum controlled, aka ported...
