New exhaust lowered mpg by 4

[Jasco]

I have a 2006 long box 4x4 six speed all stock except a bhaf air filter. The truck has 900 miles on it. I know it is not broke in yet and the mileage will get better. That's not what I am concerned about. I do not have enough miles to know exactly what my mpgs( hand calculated) are but I have driven some 100 mile round trips, all highway driving and according to the over head it read 20 to 21 the whole time. I got new exhaust installed last night and the mpgs were 16 :{ at best going the same speed. The muffler is a 41" donaldson straight thru design, and the kitty is m. i. a. I had a module on my last truck and the overhead was way off sometimes due to the different engine parameters. How could this setup affect miles per gallon this much or is the computer just fooled somehow? Any suggestions are appreciated.

 

[KBennett]

Many people have had issues with the overhead giving them mis-readings. Mine has always been within 5-10% but I hand-calculate to be sure. With a "box" or "chip" your overhead will definitely be off.



The box changes the information going to the the computer.

 

[TAbbott]

I have a 2006 long box 4x4 six speed all stock except a bhaf air filter. The truck has 900 miles on it. I know it is not broke in yet and the mileage will get better. That's not what I am concerned about. I do not have enough miles to know exactly what my mpgs( hand calculated) are but I have driven some 100 mile round trips, all highway driving and according to the over head it read 20 to 21 the whole time. I got new exhaust installed last night and the mpgs were 16 :{ at best going the same speed. The muffler is a 41" donaldson straight thru design, and the kitty is m. i. a. I had a module on my last truck and the overhead was way off sometimes due to the different engine parameters. How could this setup affect miles per gallon this much or is the computer just fooled somehow? Any suggestions are appreciated.

I don't see how freeing up the exhaust could reduce your fuel mileage unless you are now driving the truck differently or the engine is now not getting up to and staying at operating temperature. Did you recently fuel up with some different fuel, maybe a blend? I know if you were running low sulphur and now got a batch of the new ultralow sulphur that could make a small difference, but certainly not from 21 to 16. Maybe the wind shifted and you were bucking a bad headwind or you're getting a soft tire or you managed to get it stuck in 4x4 or something. Lowering the exhaust restriction should make it run more efficiently, not less.

 

[Cattletrkr]

So you have no idea what you actually got before, and you're really not sure what you're getting now. Do I have that right? What's the problem again?



Get back to us in 6 months.

 

[Jasco]

Thanks for the positve comments. I'll wait and see what the hand calculated mpgs are. Oh and cattle b f'er thanks so much for your educated post.

 

[Mark Craig]

Jasco,



We hear this on occasion as we sell tons of exhuast systems too. Most likely you are actually seeing less MPG, BUUUUUT you are also probably hearing the exhaust a looooot too!! New toys always need to be played with, once you get back to driving "normally" I bet your MPG increases.



Mark @ DPPI

 

[Nine Ball]

It has been my experience that free flowing exhaust tends to improve mileage. It has done so on every car/truck I've owned.

 

[GaryCarter]

Straight piping mine made it burn more fuel.

Playing with the pedal to get more echo off the curbs and store fronts.



It's hard to drive for economy when it sounds so good!

Gary

 

[fozzy]

If you are using the overhead as a guide have you re-set it recently? How many miles are on your trip meter?(overhead one) I was told by a dealer mech. that the overhead will be more accurate the more you re-set it ( like every tank or on a long trip). He said that it does not hold the average of the miles put on the trip meter. It resets the MPG gauge every so often by it's self. That is why one day you are getting 21 because you have a lot miles on it, then it re-sets and you have to start climbing back up on the MPG's. I have not seen any write up, but that what he said to do to keep the overhead a little closer to a true reading. It did help mine get close enough to trust.

 

[JThiessen]

I'd guess that the shop that put your new exhaust in disconnected the batteries (for welding), thereby resetting your mpg calculations.