So i decided to finally do my plugs after weeks of having them in my center console. Didnt want to do them because i was just to lazy to remove the UIM. I replaced them about 2 weeks ago and ive notice that i have lost about 3-4 mpg. I replaced the spark plugs with the recommended NGK platinum plugs. Yes the car has ALOT more pep in its step but i have been driving it the same as i have always have. According to the MPG calculator on the car im getting about 16. Is there a reason why this would happen? Also the car had copper plugs in before, so should i change back to copper since i will be installing the NWP spacers? Any help would be appreciated.

 

Maybe they're not gapped properly?

 

i checked the gap before installing seemed to spec and they didnt fall into the spark plug wells i used an old spark plug wire from another car to place them in. Thinking of putting in some regular coppers but im not sure if that would help. What is normal MPG on our 5.5 gens bone stock.

 

weather?

 

Much colder weather and short, slow trips because of iced up streets kills mileage. If the car is running better overall, it could be you are dipping into the throttle more than you think.

 

I was a little Thrrottle happy the first week but last week i was driving less aggressive. There hasnt been much ice/snow and i did 2 long trips last week which i thought would show an improvement on MPG but didnt. Will the NWP spacers help me out on my MPG and will going back to copper help as well. Thanks for the input guys

 

Where are you located?

It's about this time of year that the winter blend oxygenated fuel shows up for the northern states and everyones mileage goes to crap.

 

NYC. But why wouldnt i notice bad gas milleage before the plugs. The plugs were changed 2 weeks ago. And the weather has been pretty much constant.

 

You might be right, but I think the gas usually shows uop around now.

And depending on how much of the old gas was in the stations tanks and in yours could have had something to do with it.

Another thing to look at, how is the car idling?? Could you have a IM leak or a vacuum leak?? If you do have a leak the ECU might be able to compensate by dumping more gas in the system.

Just a thought.

 

cold weather = crappy gas mileage
new plugs are probably burning off more fuel then the old ones so the ecu has to readjust the fuel/air ratio. Try unplugging the battery over night

 

Your car is designed to use a "Laser" (double) platinum spark plug, not a standard platinum. This could account for a bit of the difference, but will really show up in the plug life. You will only get about half the life out of this plug due to faster wear of the ground electrode (where the other platinum tip is). Going to a copper plug will only neccesitate even sooner plug replacement.