I'm not sure if i put this in the correct forum topic, but I recently purchased a 2002 Chevy Tahoe. I have never had any problems with it. Today I changed the spark plugs and gaped them to .60 as it says on the sticker under the hood. Now I have a check engine light coming on, and I'm assuming its from me changing the spark plugs. I went to autozone to get new spark plugs, and the worker there showed me in the computer that the plugs require a .40 gap. I'm going back out to change the gap in a little bit and hopefully that light turns off. Do any other forum members know what I gap the plugs to? .60 like it says under the hood, or is it .40? thank you for your help.

 

I believe it's .40. Atleast I know for sure it is on 07 and up. Hopefully someone else will chime in and say for sure.

 

Try to get the code read. It might just be coincidence. Might be some other issue

 

Found this on another board, probably adds to the confusion:

Document ID# 1396703


--------------------------------------------------------------------------------


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.



GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


© Copyright General Motors Corporation. All Rights Reserved

 

Thanks for the replies. I re did the spark plugs and gaped them to .40, then i took it for a drive and everything seemed good. This morning I took it in for an alignment and the service engine light came back on. I have a code, but that code number gives me LOTS of other options it could be. It just a coincidence everything worked fine, and then i change the spark plugs and now the light keeps coming on. I also read online that you have to put the wires back on in the same place you found them. None of them were marked, so that could be a problem as well. I don't know what else to do.

 

Wow, that threw a CEL?

I've never gapped plugs. I have the tool, and I know how to, but I just buy plugs, throw them in, and have never had an issue across many, many engines, and many, many moons..

I'll research gapping and what all it impacts, but my understanding is most plugs come with the correct gap, and that's why that little piece of cardboard comes in all spark plug boxes... the tiny toilet paper looking piece.. lol

 

Thank you very much for your help.

 

Everything that I have read always says check the gap on new plugs because they're not necessarily gapped correctly at the factory. When you stop and think about it, how would the factory know what engine a plug is going in.

My experience has been that they are usually close but not exact. Would they run right out of the box, I am sure they would but it wouldn't necessarily be at 100% efficiency.

 

Every manufacture will tell you always check the gap, even pre-gapped.
Extreme care should be taken with precious metal tipped plugs Iridium, platinum..(really any plug tip)
The small precision tip can be damaged or nicked.. check the gap with a feeler gauge and adjust the ground electrode as needed... usually a lite tap on the ground will close the gap, to open it use a small pair of needle nose pliers, do not use the tip as a fulcrum to open the gap...

Incorrectly gapped plugs can cause misfire and engine knock, resulting in poor MPG and even shorten the life of the catalytic converter...

 

thanks for the reply guy. I took it to a mechanic to have the code read, so i could find out what exactly was wrong with it. It was the catalytic converter. There are 2 in the Tahoe and 1 of them is bad, but I'm am going to replace bot, and hopefully that will fix the problem.