EGR Operation

I suspected the EGR valve wasn't working on my Dad's 1986 caprice. When you applied a vacuum source to the EGR valve....nothing happened. On my other caprices, they all stall as soon as vacuum is applied to the EGR valve.

I replaced the valve with an EGR valve I knew worked, and same thing, nothing happened when you opened the valve by applying vacuum.

So today, with the car idling, I removed the EGR valve from the manifold entirely. And notwithstanding the loud exhaust noise... there's no change in idle.

Shouldn't removing the valve create a gross vacuum leak stalling the car? What's different with this car?

Appreciate any thoughts on this.

Ken

Is there carbon built up in the intake on the intake side of the valve?

Yes, it was partially gummed up. I cleaned out the deposits as best I could, and I fished a wire about 6 inches into the intake cleaning it out. But I'm not sure I'm breaking through at the other end.

Made no difference, car still idles fine with EGR off the manifold.

So is it likely plugged on the inside of the manifold? Only thing I can think of.

I sprayed some carb cleaner down there to try and loosen things up. Might try my compressor to blow it out.

Ken

Be careful, if that solid stuff finds its way into a cylinder, it could be lights out.

You likely have a positive backpressure EGR valve. There is a pilot valve within the EGR main diaphragm which dumps the main vacuum until the differential pressure between the intake and exhaust is correct:

http://72.19.213.157/files/EGRPos.gif

Thanks for that. Seeing as how the car runs fine and doesn't ping, and we don't have emissions testing here (....yet) I'll just leave it well enough alone!