'89 GMC Engine Ping/Detonation Issue

Hey everybody. I've got a 1989 GMC Sierra 2500 4x4, 5.7L 350, TH-400 transmission. Tranny's new with about 8,000 miles and the rest of the truck has about 130,000 miles. Within the past few months the truck's been having an incresing problem with engine ping. At first it was sometimes under acceleration, not too bad. But it worsened so I ran middle grade fuel. That fixed it for about a month until it started pinging again the same way. Now I'm running premium, and its beginning to ping lightly on that during express way acceleration. I replaced the knock sensor, and it had no effect, still pinging. Now what? I used teflon tape to seal knock sensor's threads so coolant wouldn't leak. Should I have not done that? Any ideas as to why the engine is still detonating like that on me, even with 93 octane fuel? Thanks in advance for any help!

Make sure the egr system is working.

I never thought of that... I'll check it out tomorrow, but how would that cause detonation? Oh and an update, I removed and cleaned all the plugs which helped a little but not much. I also made sure the knock sensor was working by putting a timing light on the engine and hitting the manifold with a hammer to see it the timing retarded and it did. I also checked the static ignition timing after the engine was warmed up and it was perfect at 0 degrees BTDC. Again, I'll check out the EGR system tomorrow morning, but in the mean time any more ideas would greatly be appreciated. Thanks!!!

Checked the EGR system, It seems to be working properly. I changed the EGR valve, checked to make sure the system had a good vacuum source. All checks out. I also cleaned the plugs, and ran some seafoam to clean out the carbon buildup. The engine runs great now, but still the pinging persists. I'm stumped!

How about the EGR solenoid? It is basically a switch that allows the vacuum to get to the EGR when the ECM commands the solenoid.

I have also seen vacuum lines that do not hold vacuum causing the EGR not to work.

//2000CAYukon

Update: I blew throttle body cleaner into the vacuum port that supplies the vacuum to the EGR system and checked all hoses and lines for leaks or collapsed areas. All checked out, but after blowing out that vacuum port pinging reduced significantly. Again, this pinging is occuring with middle grade fuel. I just realized that never checked plug gap, so I'll check that soon and post results here.