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Greetings, This morning I got bored and removed 3 random plugs just to check the condition. I noticed that one was .065in another .066in and another .064in. They also have kind of a burned look to them (black carbon, grey ash, and the center cone is a dark brown color). Should I just change them out with a new set or is this OK? I've started to notice a little shudder when idling as well as slightly lower mileage. Oh, I'm at 38,000 miles.

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Replace them! The recommended gap is now .040!





I believe it is .060 on my 01 5.3l. I replaced the original plugs at around 15K. I pulled them just to put antisieze on them and 2 of the 8 platinum discs had fallen off. I replaced them with straight copper NGK TR-55's and I replace them every 30K. Truck seems to run smoother with the coppers. If you don't want to replace them often, Iwould recommend an NGK iridium.

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Subject: Information on New Spark Plugs and Gapping #03-06-04-060 - (10/24/2003)




Models: 2004 Buick Ranier


2002-2004 Cadillac Escalade, Escalade EXT


2003-2004 Cadillac Escalade ESV


2004 Cadillac CTS-V


1997-2004 Chevrolet Corvette


1998-2002 Chevrolet Camaro


1999-2004 Chevrolet Silverado


2000-2004 Chevrolet Suburban, Tahoe


2002-2004 Chevrolet Avalanche


2003-2004 Chevrolet Express, TrailBlazer


1999-2004 GMC Sierra


2000-2004 GMC Yukon, Yukon XL


2001-2004 GMC Yukon Denali, Yukon XL Denali


2002-2004 GMC Sierra Denali


2003-2004 GMC Envoy XL


1998-2002 Pontiac Firebird


2004 Pontiac GTO


2003-2004 Hummer H2


with 4.8L, 5.3L, 5.7L or 6.0L V-8 Engine (VINs V, P, T, Z, G, S, N, U -- RPOs LR4, LM4, LM7, L59, LS1, LS6, LQ9, LQ4)







A new spark plug has been released for use in the above vehicles. The new spark plug has an Iridium tip instead of the current Platinum tip. Due to the different tip design, the gap of the spark plug has also changed. The new spark plug, P/N 12571164 with AC Delco P/N 41-985, is gapped to 1.01mm (0.040 inches) when the spark plug is made. The spark plug gap is set during manufacturing and should not be changed or damage to the spark plug may result. Any new spark plug found to not be properly gapped should not be used.

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