Pinging and knocking during pre-ignition could involve a number of systems. Here's where to begin looking.

Dear Car Talk

Dear Car Talk | Aug 01, 1996

Dear Tom and Ray:

I have a 1989 Honda Accord Lxi which knocks and pings when it is under load
unless I use super premium gas. What's actually going on when it does this?
What is pinging? -- Kenny

RAY: I asked my 12-year-old son what pinging is, and he described something
he does after he picks his nose. But I assume you're looking for more of an
automotive explanation.

TOM: Pinging, knocking and detonation are all terms for a condition known
as "pre-ignition," Kenny. That means some of the gas and air mixture is
igniting in the cylinder before it's supposed to. And when that extra flame
front crashes into the normal flame front (created by the spark plug), you
hear a noise, and that noise is pinging.

RAY: The CDC (Centers for Diesel Control) in Atlanta tell us there are four
major causes of pinging. The first three are related to excessive heat.

TOM: The first is severe engine overheating. If the engine is running too
hot for any reason, the temperature in the cylinders can simply be too
high. In that case, some of the mixture can ignite before the spark plug
fires just from the intense heat.

RAY: The second major cause of pinging is carbon buildup inside the
cylinders and on the pistons. When too much carbon collects, it can reduce
the size of the cylinders (increasing the compression and temperature of
the cylinder contents) and retain excessive heat itself.

TOM: The third common cause of pinging is a malfunctioning exhaust gas
recirculation (EGR) system. The EGR is supposed to send non-combustible
exhaust gas into the cylinders to lower the temperature of the mixture.

RAY: How does 800-degree exhaust gas LOWER the temperature in the
cylinders? Because it doesn't burn, and it crowds out some of the oxygen
that would have burned and made an even hotter flame. And if that EGR is
not working properly, the cylinder temperature can be too hot and the
engine can ping.

TOM: And finally, bad timing can cause pinging. The ignition timing
determines when the spark plugs fire. And if they're set to fire too early,
the stuff will begin to burn too early.

RAY: The use of higher-octane gas often makes the pinging stop because it
has a higher ignition point. By requiring a higher temperature to make the
gasoline burn, you reduce the likelihood of it "pre-igniting" somewhere
else in the cylinder.

TOM: But premium gas doesn't address the underlying problem. So start by
checking the EGR system, the cooling system and the ignition timing. And if
none of those things fix it, then you can consider increasing your donation
to your local oil company by permanently using a higher-octane fuel.

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