I know that this topic has been discussed many times but I wanted to share my recent experience with an EGR valve operation on one of my cars, not the 78 L-82 which has no EGR valve, which I blocked off in the mid 80's. I also did the same block off procedure in the late 70's on my Nova SS since I have not subscribed to the theory that an EGR valve does no harm to engine performance. The "theory" is that EGR valves introduce exhaust gases into the fresh intake air to be reburned in the combustion chamber of the engine providing a "cooling" effect on the fresh intake reducing NOx in the exhaust in the process. I have no doubt that this part of the emissions equation is true but as to having no effect on engine performance has always bothered me from a logic point of view as well as scientific angle-introducing 500 degree exhaust into a cold intake charge seems counterintuitive. Further, the fact that no performance engines built in the aftermarket have an EGR valve also has made me dubious of the claim that the valve does not hurt engine performance. For more on EGR valve operation read here:

http://www.aa1car.com/library/egr.htm

Which leads me to my 1994 Mustang GT 5.0 V8 and its EGR valve. The car has 30,000 miles on it and is bone stock except for a K&N cold air intake and BBK shorty headers (with an EGR valve pipe on one of the passenger side exhaust pipes to feed the EGR valve), Magnaflow X pipe with 4 high flow cats, and a magna flow cat back muffler system. Everything else is 100% stock...timing, engine temperature, etc.

The problem is that when fully warmed up, under mid to full throttle, between 3,000-6,000 RPM, the engine will ping, especially when the outside temp is over 80 degrees . I checked EGR operation (works perfectly), timing (stock Ford recommendation), wires, plugs..all good etc....everything is spot on. The Ford EGR valve will begin to open at any throttle position under load....closed at idle. Switching to 89 octane from 87 octane definitely helped the issue but did not eliminate it. Yesterday, I tried an experiment...I disconnected the vacuum port to the EGR valve eliminating its ability to open under any load (check engine light comes on since the electronic position sensor on the EGR valve detects no movement of the EGR valve). Guess what the outcome was? Pinging totally gone and the throttle response is so much better AND the engine temp actually decreased slightly from its normal operational temp. Preventing the EGR valve from diluting the incoming intake charge with 500 degree exhaust gas has LOWERED the combustion chamber temperatures eliminating the ping issue which has always been my theory for the last 30 years. The plan to eliminate the check engine light is to remove the pipe between the exhaust headers tube and the intake, capping both, reattaching the vacuum port to the EGR valve which will allow the valve to move (but no exhaust to enter the combustion chamber) which will satisfy the EGR position sensor monitor.

I am curious if anyone can explain why the supposed "cooling" effect of the EGR valve operation has been causing engine knock all these years in my 5.0 V8?

 

I am not surprised. Typically the arguements about downside of C3 emissions controls comes from either Californians, environmentalists, or one particular Forum member who constantly preaches the legal / liability issue of deactivating emissions.

As you said, why do performance engines not have any of these controls? You can believe that C3 emissions controls are important to the environment if you want, but don't try to pretend it does not kill performance.

 

Under a heavy throttle the EGR valve closes so it has no effect on the engine's performance at all.

 

Did you read the link I provided above?...there is no mention that EGR valves do not operate at WOT..and in the case of my Ford 5.0 V8 that is not true. The EGR valve operates at any throttle inputs above idle with a load on the engine. The more throttle, the more the valve opens...car actually moving..all the way to full throttle. The C3 EGR operates using vacuum as well. As the vacuum drops the EGR valve opens, all the way through full throttle, unless it magically closes at full throttle on the C3.

 

Update:

It's been about 2 months since I removed the EGR pipe from one of the header primaries and went home depot and bought two brass caps with the same threads as the intake EGR and the Headers EGR pipe thread to block the EGR gases from entering the intake @ 400-500 degrees. The car has never run better...crisper throttle response, runs noticeable cooler on the temp gauge, AND NO PINGING on a 90 degree day anywhere in the RPM range. The EGR valve continues to move under less vacuum and the electronic EGR sensor monitors the movement with no check engine light...$8 fix...just no hot gases entering the intake. Mileage has gone up AND 2 weeks ago the car passed the sniffer inspection with flying colors...CO at idle and 2,500 RPM was .02% (Limit 1.2%), HC at idle 13PPM, 19 PPM @ 2,500 RPM (limit 220 PPM)...so there you go..Better performance AND no meaningful effect on emssions..win/win

 

Sorry, but that is wrong. A C-3 ported EGR is closed at WOT.
It requires vacuum to open.

From your article:
"When vacuum is applied to the EGR valve, it opens."

 

Maybe be true for a ported vacuum EGR but either way the EGR then the EGR would be open at at all throttle positions other than idle and WOT for a C3 which would not be good for best performance? The point is that introducing 400-500 degree gases into the intake at any point is NOT good for performance or the general operation of the engine. My Mustang opens the EGR valve at any throttle position off idle

 

Correct. They are purely a smog device. I was just trying to keep it's operation accurate.
They even sell a screen you can install to keep the pintle clear of carbon to prevent the normally closed valve from being stuck open. A good accessory if you live in California, and have to endure these to pass smog.