MPG Drop after upgrades

**nlocho11** · 11-12-2009, 10:29 AM

ok so i just put in ac delco plugs and msd wires, a spectre cold air intake, oil change, brand new tires, all thinking it would improve the truck's performance. however, as the comp. is showing me, my mpg has declined from 17 to 15 average, and i'm noticing my instant econo is lower in the same places i would previously drive compared to now. is this something that will work itself out overtime and i'll see the benefits, i realize 2mpg isnt a huge loss, but i was expecting the results to go the other way. any thoughts?

**ejohnson03** · 11-12-2009, 10:48 AM

Not sure why new Plugs and Wires would be an issue, but tires will very.

Even if they are the same size. the tread pattern and material can cause a little change.

**andymax** · 11-12-2009, 06:50 PM

If it's not too much of a job, switch the cold air intake back to stock...there is a lot of data out there about them ruining mileage on some cars and improving on others. this may be a function of the computer not playing nice with higher volume of air...

**Z71_guy** · 11-13-2009, 06:19 PM

if the tire you put on are more aggressive or are heavier it will cause a drop in mileage

**nlocho11** · 11-19-2009, 12:23 PM

the tires could be it...i kept the stock 245/75/16 but went with 10ply instead of passenger tires like were on it before...could be it?

**raueda1** · 11-20-2009, 12:18 AM

Are you saying that the new tires are LT's? If so they almost certainly need sustantially more pressure that the OE passenger tires. Iif you're running them at the same pressure that could acount for loss of mileage, you''re underinflated.

**nlocho11** · 11-24-2009, 12:45 PM

Originally Posted by raueda1

Are you saying that the new tires are LT's? If so they almost certainly need sustantially more pressure that the OE passenger tires. Iif you're running them at the same pressure that could acount for loss of mileage, you''re underinflated.

yeah, the new tires (mastercraft a/t's) are running 80psi, though Town Fair Tire didnt properly inflate them as i checked the other day. put the right air pressure in and are running better now.