GM 5.3L Vortec Spark Plug Gap

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I have a 2002 Tahoe 5.3L flex fuel. Per the owner's manual and sticker on the intake box, the recommend spark plug gap is .060". However, when I look up the ACDelco spark plug for that year/engine, it pulls up plugs gapped at .040". I know GM changed to .040" around 2004, but I'm having trouble figuring out why. Did they do it to consolidate inventory with one plug for all applications? Were they having coil/ignitions failures from the wider gap putting extra stress on the ignition system? The plugs I have in it now are NGK V-power TR55 gapped at .060" and they run fine. Idle is smooth, starts easy, and no misfires, even when towing. Is there any advantage to going to the narrower .040" gap plugs on a low rpm daily driver?

I'm not as versed in ideal plug gap for engines that see low cylinder pressure and low rpm. Most of the plugs I deal with in racing engines are .010-.025".

My understanding of this is a wider gap helps with low cylinder pressure, less turbulence, and leaner air/fuel mixtures. This makes the .060" gap seem ideal for fuel economy. Why did GM move to .040"?
 
As you've said, the bigger the gap, the harder it is on the wires and coils. How many GM 5.3's are running around as we speak with gaps "worn out bigger" than .060 and run fine? If it runs ok now, and gap is set per sticker call it done. I've had very good luck running the exact NGK's you have installed.

My guess is GM went to .040 is to cut down on misfires as plugs aged. Maybe it was service engine light thing???

Remember.........You can't fix it if it ain't broke.
 
We are all forgetting one thing. The advice from your sticker is now 17 years old. The up-to-date solution is Iridium plugs gapped at .040 . GM has been putting Iridium plus in their trucks for about 10 years now. I've run one set for 10 years and 180,000 miles and they came out at 0.060 (Up from the original 0.040 ) and the truck was still running smooth. I won't leave another set in that long however, as the threads were starting to corrode and the plugs came out with a mighty "SQUEAK" . The new Iridiums went in fine and truck is running well.

Rock Auto lists 9 different Iridiums for your Tahoe.


http:www.rockauto.com/en/catalog/chevrolet,2002,tahoe,5.3l+v8,1380372,ignition,spark+plug
 
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TSB #03-06-04-060 covers your question.

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.

https://testing-public.carmd.com/Tsb/Download/42572/2176126
 
The 99-02 5.3's were some of the best engines GM has ever made. I have had 4 of them with well over 300k. Just stick with the OEM acdelco plugs and wires. Whether the updated iridium tips come pre-set .40 or .60 I guarantee you this motor will not care and will last forever.
 
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exotic metals used in spark plugs only lasts longer while costing more + conducting less, stick with standard quality NGK's as i do unless plugs are very very hard to change.
 
That's pretty much what I figured. They were just standardizing everything to 1 plug / part number. I'll continue to the use TR55 plugs.
 
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