Pinging: EGR Valve?

[chevychic]

How would I go about checking my EGR valve to determine if it's working properly? Also is the valve needed if all my smog components were removed and would a bad EGR valve cause pinging?

My truck is pinging heavily under load-actually it sounds like backfire but is too consistant like popcorn. It's to the point where I can't accelerate up hills or pass people on the freeway without it sounding like I'm chasing them down with a jar of marbles. It's like as soon as the secondaries open up, it chokes.

I've checked the timing with a light, reset the float in the carb as it was too high, adjusted the idle/mix using a vacuum gauge, replaced the fuel filter, cap, rotor, plugs and plug wires. Replaced the header gaskets and collector gaskets to rule out exhaust leaks. Now all is good and tight, and I still have the pinging.

The carb was rebuilt about 3 years ago so I don't think it's the culprit. All smog stuff has been removed by the PO.

I'm trying to start with the easy stuff before I go looking inside the engine.

This started suddenly after the truck had been sitting for about a year. I'd start it up and drive it a bit during this time, and it would start just fine but I didn't ever drive it long enough to burn off any junk that might have accumulated from sitting.

Now I'm driving it daily again while my firebird is in the shop and I'd like to get it back into shape.

Any ideas, suggestions?

EDIT: I did take a test drive with the vacuum advance line plugged to rule out the pickup coil. Not a bit of change.

[jimfulco]

A bad EGR valve can cause part-throttle pinging. The carb is calibrated to mix a certain amount of fuel with a certain amount of air. The EGR allows inert exhaust gas into the mix at part-throttle, so the carb is set for a little less fuel, since the exhaust gas displaced a little of the good air. When the EGR fails, there's more good air available, but the carb doesn't know, so there's not enough gas for all that good air, thus it runs lean and pings.

I don't know how the EGR is hooked up on an '86, but on my '78 Skylark, all you had to do was disconnect the vacuum line from the EGR valve and plug it, then it would ping like there was no tomorrow at part-throttle. When it started pinging like that with the hose connected, I knew the valve was bad. If you can get some suction on the hose (MityVac, mouth, whatever's available), you might find that it wont' hold vacuum, or that the valve mechanism doesn't move.

Sometimes the valve may still be good, but the exhaust gas passage is blocked by coke deposits. If so, try to scrape or drill out the deposits until it will pass gas, then see if it still pings.

[chevychic]

I tested the valve to see if it operates by pushing on the diaphram while the truck was idling. It caused the rpms to drop as expected per my Chiltons. It got too late to try to pull a vacuum through it, but I did have time to remove it and make sure the intake port was clear. I found the valve was caked with soot so I cleaned it off real good and put it back on the truck. We'll see tomorrow if it runs any better.

All other emissions stuff has been removed from the truck.
Another question...would the EGR valve have an effect on exhaust smell and soot?
My truck has always had a strong exhaust smell even when the timing and idle mix were adjusted properly and if you start it with any object within 6" of the tailpipes, there will be black soot spattered on the unsuspecting victim....could be fun if you happened to be mad at the victim at the time...don't ask me how I know this

It would be nice to know I could tone this down by replacing the EGR valve.