Dual Exhaust Mileage Drop

[robig]

I have a 2007 Silverado 1500 Z71 5.3. I installed a cat-back Flowmaster dual exhaust. Once on the truck my mileage, which was close to 17 mpg, dropped down to 12 mpg. ?????

[omegafiler]

Stop giving it so much throttle.

 

But seriously, there is no reason why a cat-back would cause that much of a loss in MPG by itself unless something else was wrong. Or you're just unknowingly using more throttle than you used to because you love the way it sounds. Which wouldn't be the first time that's happened.

[robig]

The heavy-foot syndrome may have been true at first. However, after I saw the drop, I ran through a couple of tanks of gas--being extra careful--and the mileage was the same.

 

Flowmaster told me to reset the computor, but I was told that this could not be done in the '07 models.

 

The Flowmaster unit does sound nice, but with the price of fuel I'm considering going back to stock.

[Darkanion]

Well, if it's not HFS, I think I'd have sensors checked before I put the old system back on. I doubt the exhaust is actually causing the problem. But, there is a possibility that an O2 sensor (or something else) maybe got unplugged during the install. That could be throwing off the computer, causing it to burn a lot more gas.

[Truckin2003]

I'm no mechanic but i believe bad O2 sensors and cause a decrease in fuel mileage. maybe one got messed up by accident when you were installing the system.

[formulation]

I installed a Flowmaster system on my '06 Silverado w/5.3L auto and saw a drop in my city driving of about 1.5 MPG and just a slight drop in Hwy MPG. It was worse at first but then seem to improve.