I've been trying to help my dad figure out why is truck pings so bad on 87 oct. gas. It's a 00' with a 318 with a 5 speed tranny. It has 118k, fresh plugs,wires , cap, rotor, and no plenum leak. He keeps her in good condition but for over a year he has had to run 92 oct to minimize the pinging. He lives in Ca. so I do what i can over the phone. Carbon deposits on the valves maybe? Thanks in advance! And no CEL.

 

are you sure about no plenum leak ? this is the most common cause. take a peek down through the TB with a flashlight. a cooler plug (3923) and 180 tstat might help a smidgen, maybe not.

 

Seafoam it. Twice.

 

He checked the plenum the other day. He pulled it up on ramps and looked down the TB and said it was dry as a bone. I'll tell him about the seafoam. Thanks again.