my truck is a deluxe model pickup circa 1993 3vz v6 with 150k in it, runs very very well and gets close to 24 mpg. I drive like an old man so that sorta explains the mileage. Problem is a ping below 1500 rpm, engine hot,light load going mostly up hill or light acceleration. Seems to be getting worse. It used to ping badly and I upgraded to top grade gas and the ping went away and the mileage increased 9%.
I have checked timing which was a tad advanced (2 deg), increased spark gap .010, tried a new knock sensor in a remote location with a new pigtail which the ecm did not see at all & read the 52 code. No code on the old sensor, no change in the ping with the new one, but slight change in performance perhaps. The wiring to the ecm showed no resistance.
denso platinum plugs gapped @ .042, mass air flow meter checks out, egr checks out, tps checks out, temp gauge reads normal, plenty power throughout the rpm range.
Only thing I see not right is when I check the timing with te1 and e1 shorted, when I remove the sst the timing does not advance the 5 to 7 degrees the book says it should. it advances plenty when I rev it though.
I have swapped put the ecm, and igniter from my daughter’s 94 which is the same truck. None of this shows up on her truck even with my parts installed.
egr valve passes tests and is spanking clean inside. Passages are clear.
I have run seafoam as a top end cleaner both through the tank and directly into the intake.
What puzzles me is that the truck runs so well at higher rpm & load, but pings under 1500 rpm under light load. Even when I push just a little bit more on the gas, not enough to speed the truck up, the pinging stops.
My friends tell me to just drive around with my foot in it and stop driving like grandma.