Ever since I had a Magnaflow cat back installed on my Truck I've noticed a significant decrease in gas mileage. Techs @ flow said that this was normal untill ECU relearned free flowing exhaust pattern after driving 300 to 1000 miles, or after a reset of the ECU by removing negative wire frim batt and then allowing to idle then drive 1 complete cycle. haven driven 1000 miles plus 3 resets I have not gained any increase in gas consumption. Have any one else suffered this or similar problems with a cat back system? The exhaust was proffesionally installed and the truck only have 47.000 on the dash.

 

What engine? 2X4 or 4X4? Previous and current mpg?

 

I never really computed mileage because of no trip odometer, however the mileage was good, now it has plumeted, I drove about 50 miles today @ speeds of 50 to 85 and used a little less than 1 qt of tank.

 

In order to intelligently discuss your fuel mileage, you must be able to accurately compute your fuel mileage. And yes, you have a trip odometer. 'About 50 miles and burned about a quarter tank' means nothing. Are you a product of our wonderful public school system?

 

Let's not started shall we? I just realized that the trip odometer is the same as the mileage indicator (duhhhh) any way when I tried to reset the trip mileage back to zero it will'nt allow me to. Is it a way to do this or is mines damage? the engine size is 5.4 and it's 4x4.

 

I figured it out, thanx

 

The mileage on the truck has improved since last post here. I'm really impressed.

 

i had the same problem. i installed my magna flow exhaust system and my mileage went from 16.5 to 13. it took a while but it went back to around 16.

 

Ive had my 04' FX4 scab for a month or so now. I have 1,600 miles on it. I installed a Magnaflow cat back si/so w/ stock 2.5 input but went with 3" output w/ stainless tip. ($320 w/ install)

I regret not doing a mileage check before installing it. On my last tank I got 12.3 MPG. This is a 20 mile commute to work and some in town driving. Moderate driving with 70-75 MPH highway speed.

Im not upset with this, however, Im not pleased either. Can I get some input on MPG.

Will this get better? When? What about when I put on an Air Force intake kit?

Stu

 

Stock, i get about 14 in town/highway. best i've ever seen with this truck was 16 constant 80mph on a trip to phoenix and back.

That's a 5.4L, 4x4 supercrew.

 

With the weight of these trucks and the low torque output in the normal running range, you have to open the throttle farther to get the power to maintain road speed.
The more the throttle is open the more fuel is metered into the engine.
Look in the rear view mirrior to see all that fuel you leave behind......doing this.
Fact of life and science.

 

I estimate i can get about 100 miles (give or take) on a 1/4 tank under normal driving conditions, with the occasional heavy foot, mix of freeway and stoplight to stoplight miles. Which puts me at about 425 miles to the tank, give or take... which puts me in the average of about 17MPG... 14 - 15 if i get on it more often... i have a 97 4.6L

 

Since this thread topic is fuel consumption,
a report hot off the road this evening.
4.6 Screw, 3.55 gears, total weight 5900 +/- lbs.
Conditions, 20 to 26* temps, Pocono mts. Eastern Pa. 138.6 miles round trip with some idle time and a small amount of 4wheel drive use on 8.35 gal of Gulf 87 out of the same pump. Thats 16.5 mpg in cold weather. Road speed 60 to 65 mph with partial Cruise control use on level road.

 

in cold weather arent you more likely to get better fuel economy? Regardless of how cold it is outside... the intake warms up the air as it makes its way down the chute... but having slightly cooler air is actually known to help out the ignition process... thus the reason for "Cold Air Induction"

 

the iat will read cooler temps and add more fuel