Hmmm...I've been keeping track of my mileage, MPG, gallons bought, etc at every fill up since december 2011. I think I'll put mine in a spreadsheet too, and we'll see how my 4.7 compares. It'll be a few days until I get around to it though.

 

Well..... I took the Durango out for a romp after replacing the muffler and tailpipe. While cruising down the highway I got up to 18MPG! I was getting 16MPG at best before. I replaced the TPS/IAC Sensors and give it a thorough Throttle body cleaning...also replaced the plugs a few months ago...but it looks like the IAC/TPS/TB Cleaning actually helped! LOL.

New muffler is a Walker Quiet Flow with Walker Intermediate and Tail Pipe. Sounds OEM for the most part. "maybe" a bit thoatier when accelerating with "authori-TAY"....maybe just my imagination too. But very happy with the install.

J

 

Mine does ok around town and highway towing without o/d. Highway with O/D it can't do, idk why it struggles to calculate that.........

 

You would think the thing would be accurate, after all it accurately has your miles driven, and how hard can it be to make a reasonably accurate flow meter. Could part of our discrepancies be due to how we fill the tank? I suspect just letting it click could be different for different pumps/stations.

[Edit: I looked at the FSM after posting. It appears that the system uses the fuel tank float for the math, not a real flow meter. Since it is an arm/float deal, I suspect it's not linear (I've never seen one that was, arm arc, tank shape, etc). That would mean the accuracy would be dependent upon the tank level as we drove up to the pump.]

 

Every time I fill up, I reset the computer. With two tires in the back I was doing 14.1-14.2 mpg average.

Even tried to take turns hard to see if it affects the computer, but then I realized the float most likely has an anti-slosh thingamajig :P

My commute one way is about 12-13 miles, so based on the computer I'm burning a little less than 2 gallons per round trip commute. I top off once a week and usually by the time I fill up I'm slightly before the halfway point and I fill up to where the needle goes past the full mark which is about 12-13 gallons. So if I burn 2 gallons a day for a week it's about 14 gallons.

For me then the computer is pretty accurate. Not 100% but just enough to give me an idea. And I drive with O/D on. On drives I watch the computer like a hawk. Maybe I should clean the TB and check my sensors to get jjjefferson's mileage lol.

 

My trip displays is sometimes spot on. But most of the time it can be up to 1 mpg less than actual mpg calculated manually. Never seen the trip display will ever show higher mpg than manual calculation.

I avg around 10-11 in town and 13-14 on hwy. Looking to replace my cat on the exhaust to see if it will help bump up my mpg as I am just now over 130k.

I've done this with my 85 dodge shelby and noticed a jump in power and mpg even tho the inspections say the cat is fine. But replaced anyway. The original cat was way long and looks restrictive and the new magnaflow short fat cat had better flow.

 

According to my spreadsheet the overhead is on average accurate withing ±2.92%

I've been thinking about replacing the cat too eventually, after 15 years/164k miles it's gotta be getting gunked up.

 

I may just go straight pipe and ditch the cat with some custom tuning to delete that. I don't have to do any emissions testing here ......

My computer is usually on the low side for mpg's but has been as much as 2mpg high and at 11 mpg that isn't good. I always thought that the computer went off of injector pulse rates to calculate fuel economy? If that was the case with new factory injectors varying by +/-4% I could see it being off, especially with older fuel pumps.

 

There's no inspections at all in SC, but I am planning on moving back to PA after I finish school and they have some of the most rigorous inspections in the country, so I'm not going to be able to get away with that. Really all you'd have to worry about is disabling the CEL from the downstream o2 sensor since all it does is monitor the cat (doesn't affect running at all).

 

I already have the tuner and can tunes from hemifever so its just an upcharge to start removing stuff, but back on topic. I will start checking my overhead to actually contribute here once I have my trans done. Also does anyone know specifically how the trip computer calculates the average? Does it use the injectors or is it of the fuel level in the tank?