Chevrolet Repair: 92 K2500 w/350 badly pinging when warmed up, coolant temp, lean mixture

Question
I have a 92 K2500 with a 350 - 170,000. When the truck gets up to operating tempurature, it will ping terribly - but only at part throttle.  It seems not to ping under WOT, but it's certainly down on power.  After getting a the infamous code 32, I replaced the EGR valve and EGR module. It didn't fix anything - the EGR port was blocked with carbon.  Next I removed the intake and cleaned the sludge from the top end (had the intake soaked in an acid hot-tank for a weekend).  The truck STILL pings very badly once it gets warm (when it's cold, it runs fine) and it's smoking a bit too.  The smoke seems to be oil-ish, but it's been running rich for a long time now. It has a new O2 sensor and a fresh set of plugs.  I'm stumped.  Any ideas?

Answer
Hi Aaron,

I found this question in the question trash can.  Once it ends up there, any of us experts can answer it.  I hope this helps.

Well this is a thinking one for sure.  Lets start with the reasons for ping (detonation or pre-ignition):  

Engine too hot
Wrong gas
Lean mixture

Most if this answer is me thinking out loud.  I do this so you can see where I am comming from.  Maybe my thoughts will trigger your own ideas.  Together we can figure this out.

You comment "when it's cold, it runs fine" could indicate the motor getting too hot.  Is it?  Coolant temp sensor is the choke nowadays.  If the coolant is low, this will read wrong.

Are you using a too low a grade of gas?  Did you try a higher octane?  If you didnt need it before, you probably dont need it now.  

Lean mixture.  Well this has many causes.  Weak fuel pump.  Plugged fuel filter.  EGR issues.  Intake plugged up.  O2 bad.  These I am sure you ruled out.  

Now what is left.  Vacuum leak.  MAP sensor bad or vacuum to it broken.  Faulty fuel pump regulator.  vapor lock from gas tank not venting (loosen gas cap).  Fuel pump failing.  Intake air getting in past the Air Intake sensor.  This can be caused by a loose air intake duct.  Coolant sensor or Air Intake sensor is false reading.  

I am trying to remember if carbon build up in cylinder causes ping.  I think I remember that it can.  I may be wrong on that.  

Is this on one cylinder only?  If you dont have DIS, try disconnecting plug wires to see if the pinging goes away. If you have DIS, disconnect the injector for each cylinder one at a time.  This may pinpoint a particular cylinder.  May point to a lazy injector.  

I hope these ideas help.  If not, it may point you in the right direction.  Get this fixed before the piston gets a hole in it.  

C J S