so i have a 5.7 hemi and a diablo 93 octane tune. I just installed my pacetter long tube headers and dropped my cats. I only have my front O2 sensors pluged and my rears disconnected which i obviosly gives me a check engine light...The problem is my fuel economy dropped severly...Does anyone know what the reason for this is? I'm planning on staying catless but do I still need to have my rear O2s in or what? Someone help cause Im literally getting like 9 to the gallon which is ridiculous lol

 

Wow, my mileage, as long as I stayed out of it ( ) went up after the header install. Did you add or remove fuel to compensate for the headers? Did you add anything to make it run richer ie 180 t-stat or powerwire? How long have you had the headers installed? if it has been a while thats one thing but if its recently maybe the cooler weather is adding to the problem. I know I get worse mileage in the winter by 1-2mpg over the summer due to the weather and gas (although the truck feels much better when its cool outside).

 

Oh for your rear O2's you need to do the non fouler trick to get them to not throw a cel and read right. Also need to get a wideband O2 in there as well.

 

what does the wideband O2 do? I've had them on for like two weeks now...I"m guessing its runnimg extememly rich but I don't know why. I didn't do anything else...just the headers and no cats...

 

The wideband will read the AFR and tell you if you are running to rich or to lean. Have you done the nonfoulers with the rear O2's already? Most of the time long tube headers will lean the system out quite a bit sometimes to the point that they willl throw a code for being to lean

 

i'm running the pacesetter long tubes as well. It did of course throw a cel, but i went ahead with a custom tune and fixed a few issues at once. As far as you getting 9MPG i would pull i think it's fuse 15 to reset the computer. I did a lot of things all at once, but i gained milage.

 

You sure you are not just "gettin' on it" since the headers went in? All things being equal you should gain fuel economy. More efficient breathing coupled with a slightly leaner mix would gain an MPG or two.

My CAI, tuner & headers leaned me out quite a bit. Not quite to throwing a code, but pretty lean. I did the 180* stat band aid to richen it back up a tad.

You really didn't need to omit the cats, they actually are pretty high flowing for stock cats and keep just a tad of backpressure in the mix for low end torque...

 

I also have Pacesetters and cat-less and as said above, put the front O2s back in and use non-foulers stuffed with 0000 steel wool on the rear O2's. other than that, try resetting the PCM to make it relearn everything.

 

1-2 mpg is basically 15% increase Hammer. Aint gonna happen. He might see a 5-10% increase if he keeps his foot out of it (which would be like .8 mpg).

In any case, if you're only gettin 9 mpg my guess is you're runnin wayyyyy too rich. Pull a couple random plugs and see if they've got any carbon on the tips. Do a PCM reset just to be safe.

 

So those running no cats where are you placing the rear o2s? The fronts go in the bungs on the headers correct? I'll be installing mine soon. I already have 2 non foulers from moes.