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Old 11-20-2001, 11:41 PM
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Join Date: Oct 2001
Location: Tampa
Posts: 73
damage to engine from lower grade fuel/knocks

I looked at a '94 E320 Wagon today. The current owner is not a car guy and admitted to calling his mechanic at one point complaining about pinging noises from his engine when climbing hills. He was using regular grade gas. He immediately switched to premium.

What's the danger of significant damage to the engine from knocking? Should I walk from this car? I do not know how long he drove with lower grade fuel.

Thanks in advance.
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Old 11-21-2001, 08:59 AM
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Any MB gasoline engine as far back as the mid eighties has a knock sensor which supplies information to the engine management computer which will retard timing to prevent spark knock. If the knock was just for a second then the system is working correctly and retarded the timing properly. If the knock was continuous, there is something wrong with the system.

If there is something wrong with the system causing the knock to be continuous, it can damage piston tops. In the old days of high compression engines, no engine management computer with knock sensor and low octane fuel, spark knock would put a hole right through the top of a piston.

Every time you here that knock it is the equivalent of a LARGE ball peen hammer hitting the piston top. The force is applied quickly and to a very concentrated area of the piston top.

I would try to ascertain if the knock only lasted a second or so and then went away. If so, you probably have nothing to worry about.

Good luck,
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