So, I have been doing hand calulations as well as the overhead displays...

Well...

I filled up the other day, drove 35.2 miles on 2.032 gallons of gas, in town.. 17.347mpg hand calc'd... 17.2overhead

I filled up after a 68.7 mile highway trip... took 3.337 gallons or 20.587mpg hand calc'd... overhead, 19.2

I filled up after a 51.8 mile highway trip.. took 2.363 gallons or 21.921mpg hand calc'd.. overhead.. 19.5

I filled up after 26.7 miles in town, took 1.562 gallons or 17.093mpg hand calc'd(this is also in the hilliest town I've ever drove in... 15 - 20% grade hills... that I always have to drive up..) overhead... 14.7

I then drove home, at 81.6 miles highway, took 4.006 gallons or 20.36mpg... overhead 20

So... I dunno about you guys, but my overhead is way off for the most part....

However, I like my mpg's... :-)

 

Ya, I dont have the overhead thing, which sounds like a good thing LOL, I'd be cussin it rigth out the window. But 20mpg is soundin good. I just ionstalleda power wire in mine, reset PCM.noticed better cruising so far, but only 35-40 miles so far

 

ya, I think mines off too

 

I hope mines off...it says I average 12.6 MPG. I'd say my whole ting is off since the other day i drove by two bank temp thingies and they said 91...mine said 78 ....hmmmmmmmm
Guess I need to bring that up at my next service.

 

If your overhead trip computer's MPG
does not agree with your hand calculations
that is usually a clue
that either
your fuel pressure is below/above specification
or some of your fuel injectors are partially clogged or otherwise malfunctioning.

But I would not worry about things not exactly agreeing when we are only talking about 2 to 10 gallons because it is impossible to fill your tank by hand to exactly the same level.

The gas tank is designed to trap an air bubble so that the vapor from the fuel can be controlled. The size of the air bubble varies with how level the pavement at the gas station is.

Keep track of the next 100 gallons by hand and compare it to what the overhead trip computer says was gallons used.

The 'other side' of any MPG calculation is the miles
and I would bet that your odometer is reading 4-8% fast
so MPG calculations are off this much too.
All new Chrysler vehicles that I have test driven
and at least two 4.7V8 Rams I have rented have read fast.
It has been too consistent to be random
and I suspect it 'consistently' saves Chrysler about 6% in warranty costs.

In Chrysler's defense they would probably say they set the odo/speedo on the high side so that it will read more accurately as the tread wears down....and so they won't be sued as having caused someone's speeding ticket.

 

what is a power wire to the pcm ?? is that a mod ?

 

I don't have an overhead display. When I calculate mpg I fill the tank and reset the trip odometer. Then on the next fill up I record the miles I drove and how many gallons I put in. I then divide the miles usually anywhere from 194 to 214 miles by the number of gallons. I never let the gas gauge go below the quarter mark so I put in anywhere from 14 to 17 gallons. This seems to me to be acurate but since I don't have the overhead computer to compare it with its hard to tell.

 

They aren't going to be right. It has too many variables to calculate. They probably did that on purpose.

 

Power wire is a wire with a resistor in it that you add inline with the IAT sensor. Makes the Fuel injection think its got colder air, and thus, advances spark timing a little at cruise RPM, as well as add some more fuel at WOT. The PCM is Powertrain Controll Module. It's basically the brains of the truck. It also learns how you drive, and how the truck responds, etc. WHen adding new mods, it's adviseable to reset the PCM so that it starts fresh with the new mods that are done.

I found out about the Resister in the IAT trick from this form thread http://www.dodgetalk.com/forums/show...ght=Power+wire
So, me being a Electrician myself, I made one. Used Weatherpack connectors so I can remove the wire easily, not that I'll think I'll need to. Also, the lnger wire will work great with my IAT sensor relocation in my CAI tube

HAHA I see that forum is not alowed here LMAO. FOr those who really want to read about it, type in dodge talk in where the astericks are in that link

 

I actually think in the examples you stated that it was very accurate, if its within 1mpg, I'd say that thing is pretty good. I thought they were BS but seems like there the real deal.