Can spark plug gap affect mpgs?

[Mongo]

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I have a 2003 Suburban and just changed out the AC Delco spark plugs. I gapped the new Autolite platiunum plugs to .60 as stated in the owners manual and repair manual. However, the plugs I pulled out were gapped at about .50 to .53, the 2004 spec. Now, I've lost about 3-4 mpgs on my driving. Does the spark plug gap affect the fuel efficiency that much? Should I pull the plugs and gap them to the 2004 spec? I also changed out the AC Delco fuel filter with a WIC fuel filter. If anything, I expected the mpgs to improve NOT worsen. Any thoughts on this anybody? Thanks!

[73shark]

Probably should have stuck w/ AC Delco plugs gapped at the recommended gap. For whatever reason, current electronic ignition systems are sensitive to plug brand.

Put some Bosch platinum plugs in a Dodge minivan once and mileage and power fell off. Replaced w/ some new Champions which it came with and everything was fine. And the platinum electrode on the Bosch was completely burned away down to the insulator after about 1K miles.

[Mongo]

Interesting...thanks! The AC Delco plugs weren't gapped to the recommend gap though. They were gapped to about .50-.53 whereas the recommended gap is .60. Will I make things worse if I pull the plugs and regap them to .53?

Originally Posted by 73shark

Probably should have stuck w/ AC Delco plugs gapped at the recommended gap. For whatever reason, current electronic ignition systems are sensitive to plug brand.

Put some Bosch platinum plugs in a Dodge minivan once and mileage and power fell off. Replaced w/ some new Champions which it came with and everything was fine. And the platinum electrode on the Bosch was completely burned away down to the insulator after about 1K miles.

[JennaBear]

I would suggest gapping to .04 inches. GM revised their specs to .04 since the original .06.

[Mongo]

Thanks, JennaBear! I'll that a try and see how she responds. Appreciate it!

[JennaBear]

You will be surprised the difference that a gap change can make!

[Black Dog]

It can absolutely affect mpg, and performance, efficiency. It can only be gapped correctly or it gets worse from there. Too little gap is like muting it and too much is like misfiring. If you're not adjusting it in consideration of the ignition system, combustion chamber, fuel induction and things like that then you should probably just go with the plugs recommendation.

[MRGREG5000]

I only use ngk plugs in my hoe.....ngk makes ac delco plugs and ac delco robs you compared to the ngk equivelent......use ngk tr55 gapped to .40

[KarenCaren]

Wow. that gap changes a lot in mpg. Thanks for giving me the info about the gap. When I change mine I will definitely go for 0.40 gap.



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[MRGREG5000]

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For years the debate has been to use ac delco or not to use ac delco........first and foremost ac delco is made and manufactured by ngk.......why buy ac delco when the same plug ngk makes is 1/3 of the price.......ac delco is almost 50.00 a set of 8 for my 99 tahoe.....ngk same plug .....19 dollars and change.......dont be fooled buy people who say only use ac delco......do some research and youll see the truth.....and some tahoes came with ngk from the factory depending where they were assembled......now chevy used to state ....gap the plug at .60.......it even says that under my hood on a sticker.....but now chevy changed it to .40,,,,,,,the .60 gap makes a tahoe idle ruff.....the idea is that the bigger the gap you can go with a smmoth idle than the better performance youll get......but less mpg.....the closest more mpg less power.......you can gap the ngk to .50 if your tahoe runs smoothly......i gap mine to .40,,,,,,,ngk plugs are pregapped to .40 and you just make sure they are.....now ..........the ngk plug you want is .....ngk tr5.....or ngk tr55........the tr55 is a hotter plug.....better mpg with tr5....i have tr5 gapped at .40,,,,,,good power and mpg......good luck and dony pay 50.00 for 8 spark plugs because they say ac delco..........OH YEAH .....DONT EVER USE BOSCH....CHAMPION....IF YOU WANT TO BE DIFFICULT YO CAN USE AUTOLIGHT IF YOUR IN A JAM, BUT NGK....NGK...NGK...NGK...NGK...