1988 suburban pinging

[kerjer19]

Could any one give me suggestions on what might be causing pinging on acceleration? 1988 3/4t 5.7 4x4. I have already checked the timing, and changed the anti - knock sensor. I am using high octane fuel with octane booster. Nothing seems to work. Any help would be appreciated. thanks in advance.


kerjer19

[KShortell]

You say you've checked the timing. I'm assuming you checked it at idle. You might consider using an advance timing light to see what the timing curve is like and how much total advance is pulling in at 3,000 rpm or so-- full mechanical advance should be pulled in by then.

Checking mechanical advance (with the vaccum plugged) should yield no more than 32-34 deg. BTDC at full advance. You'll get pinging for sure if you have more than that. The anti-knock system can only retard the timing so much- to 0 vacuum advance, but the mechanical advance is basically a set parameter.

I ran into this on my boat's engine. I blew two head gaskets before I finally solved the problem. My advance mechanism's limit stop had worn, allowing 42 deg. BTDC advance!

Good luck!