1999 GMC Sierra Spark plug covers

1999 GMC SIERRA
179,000 MILES • V8 • 2WD • AUTOMATIC
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GWATS1957
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Each of my spark plugs has a metal sleeve over the plug wire near the engine block. what is this for?
Mar 7, 2010 at 8:05 AM
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CARADIODOC
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They reduce radio frequency interference (RFI) from interfering with the multitude of computers. The magnetically-induced voltages can be greater than some of the tiny signal voltages coming from the sensors and the computers will think the various spikes are sensor problems.

caradiodoc
Mar 7, 2010 at 11:35 AM