i got true dual straight pipes and didnt notice a difference in MPG when i drove it like i did but let me tell you that it is hard to do with the sound it talks you into taking off hard and keeping on it... i think that is where you gas is going. Drive it like a grandma and see how it does and keep your foot out of it or expect to pay the bill.

 

Ummmm the post O2 sensor has absolutely nothing to do with the way the engine runs. It only sets a CEL if your Cat goes bad. The pre O2 sensor controls the mixture.

 

It didn't really make much difference in my mpg's when I got my straight pipes put on. Possibly a little bit of a drop, but that could be because I tend to push harder with my right foot these days than I used to. I'd say try and drive with a lighter foot and see if it makes a difference, then do somethin' else. But don't hope for anything very high and just enjoy the truck!!

 

yeah.....
umm you need a decent amount of backpressure to regain your low-eng power and MPG...

keep cat gutted, or install a high flow cat, and at least a box type muffler - "flowmaster, etc"
not a straight thru glasspack... =no backpressure

umm on a 2001 truck right??
You should DEF. have a downstream o2 sensor...
maybe someone removed it completely?...

 

My MPG went up about 2-3 MPG when I got rid of my Cat and went to true duels and Magnaflow mufflers. Most likely it's because the Cat was bad. But I never had a CEL before or after I had this done. I had the shop put the post cat O2 sensor back in just in case.

 

Why do you need back pressure anyway? What does it do, and how does that increase low end power and MPG?

 

thats what were talkin about...

 

XXL- when I got it, it had 3 inch off the cat, that was welded on after-market, and it didn't have a post cat o2, maybe someone did remove, but it runs okay, and it doesn't throw any codes or anything like that, no wires hanging down there either.... is there some way I can trace a wire off the PCM to find if it ends in a simm or something like that?

 

Everyone else is talking about the post O2 sensor. The post O2 sensor will not have any affect on the way the engine runs. The only reason for a sim is so that you can pass emisions. If you CEL light is on you won't be able to pass emisions.

I reread your post and you were talking about the precat 02. You can't put a sim on the front O2. The engine won't get the correct mixture and you'll either be way to lean or way to rich. The precat O2 is extremly important in the way the engine runs.

 

I know this is going to create an argument but here it goes. Backpressure is a bad thing that is commonly misunderstood. It used to be thought that backpressue would help to close the exhaust valve quicker giving you more time to fill the cylinder with air and gas giving you more perfomance. If this was the case why aren't we all running 1" pipes. The truth is you want the exhaust gas to have a constant velocity. This way exhaust gas can move freely and smoothly out of the system. If you throw a 6" pipe on for your exhaust then when the gas leaves the cylinder it's going to expand causing it to slow way downand rob you of performance. So you need to strike a balance. Something small enough that the gas dosen't slow down and something big enough that it can still move freely. If you get this balance correct then the momentum of the gas will actually create a negative pressure behind it (It sucks). This will create a negative pressure in the cylinder helping the exhaust valve close and increseing the amount of air into the cylinder.