here's a dumb (?) one
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Senior User
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here's a dumb (?) one
I hear about pinging all the time. I know what a lot of engine problems sound like, as I've had most of em 
how do i tell if my engine is pinging/detonating?> I know what it means, it means the a/f mix is detonating in the combustion chamber before the spark plug fires.. right? but how do i tell if my 84 351c bronco is doing it? what kind of noise or what does it make?
- Sean
how do i tell if my engine is pinging/detonating?> I know what it means, it means the a/f mix is detonating in the combustion chamber before the spark plug fires.. right? but how do i tell if my 84 351c bronco is doing it? what kind of noise or what does it make?- Sean
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Joined: Aug 2001
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From: Delaware
Your definition of detonation is close, but not totally correct. Pinging/detonation is a result of the a/f mixture expanding too fast after the ignition and causing a shock wave. This shock wave sometimes produces the audible noise known as pinging. This sound is identified as a light rattle under certain load conditions. It most often occurs at low speed under heavy load, such as pulling a hill in high gear. It can also occur at light gas pedal coditions, when the mixture is slightly lean. Just because you don't hear pinging, doesn't mean that some detonation is not occurring. Some later model vehicles have 'knock' sensors built-in. These retard the spark if the 'knock' sensor detects any sign of the audible sound of pinging. Removing the EGR valve can cause pinging, because it creates the 'lean' condition which contributes to pinging.
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I have always heard "pinging" referred to as pre-detonation. It sounds very similar to a valve rattle. Pre-detonation means the fuel mixture is igniting before the spark. it can be caused by several things. Carbon build-up on the vavles can create hot spots that will ignite the a/f mixture before the spark. An overheating engine can cause pinging and high compression ratios combined with low-octane fuel can cause teh engine to act like a diesel engine and ignite the a/f with out a spark. Pinging is very bad for an engine. At a minimum it can cause pitting of the piston and in bad cases can actually damage heads and valves. as an added note higher octane fuels or octane boosters added to fuels help prevent pinging by raising the burning temperature and presseure of the a/f mix. a lot of vehicles will ping going up hill with the air conditionor running
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Joined: Jul 2001
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From: Gainesville, FL
All,
Everything stated previously is pretty much on the money. At a certain pressure and temperature, a given air/fuel ratio will combust. If the motor runs hot enough, you will not need a spark to set off combust. The higher the pressure the lower the temperature required to meet this condition. This is why high compression engines suffer worse than low compression engines. The further you advance your timing, the more pressure is developed at Top Dead Center (TDC). After TDC pressures drop and the condition is alleviated.
Why the "Ping"?
Normally, the A/F mixture burns under a controlled condition. Constant expansion, at a constant rate (approxiamately 0.002 seconds), if I remember correctly. During a ping, the A/F explodes and peak pressures are instantanenous. I think this is where the expression "Ping" comes from.
The leaner the A/F mixture, the less energy is required to raise the temperature. These two conditions, lean A/F and increased pressures, contribute to "pinging".
Consider it,
KingFisher
PS Pinging sounds almost like a rapid rattling. Stepping down on the gas (enrichening mixture) can usually alleviate this condition.
Everything stated previously is pretty much on the money. At a certain pressure and temperature, a given air/fuel ratio will combust. If the motor runs hot enough, you will not need a spark to set off combust. The higher the pressure the lower the temperature required to meet this condition. This is why high compression engines suffer worse than low compression engines. The further you advance your timing, the more pressure is developed at Top Dead Center (TDC). After TDC pressures drop and the condition is alleviated.
Why the "Ping"?
Normally, the A/F mixture burns under a controlled condition. Constant expansion, at a constant rate (approxiamately 0.002 seconds), if I remember correctly. During a ping, the A/F explodes and peak pressures are instantanenous. I think this is where the expression "Ping" comes from.
The leaner the A/F mixture, the less energy is required to raise the temperature. These two conditions, lean A/F and increased pressures, contribute to "pinging".
Consider it,
KingFisher
PS Pinging sounds almost like a rapid rattling. Stepping down on the gas (enrichening mixture) can usually alleviate this condition.
