My truck averages 14.4 mpg empty on winter fuel, and Dad's averages 17.8, and we basically have the same driving style. The trucks are almost identical, except his is a 2001 HO with I'm guessing DDII injectors, and mine is a 1998.5 with 275's. They both have VA boxes and exhaust brakes. I cleaned my IAT sensor a while back, and it made little or no difference. Would replacing it help? What about the map sensor? I can check resistance on the IAT sensor, but what is the proper way to check? I maintain these trucks very well, tire pressures are correct, no dragging brakes, etc. Thanks a lot

 

In your discriptions you did not put the gear ratio , that could be the diff. , then theres the 5-6 spd diff also.

 

Both trucks are 3:55, and I would not think the slight difference in gearing of the 5 vs 6 speed would make much of a difference. One thing I forgot to mention is that my truck is supposed to have 215/85/r16 tires on it, but I am running 235/85/r16 tires. To compensate for this, I add 4% to my mileage, which I have read is the difference between the 2 sizes.

 

I checked the resistance on the IAT, and it is within specs per the dodgeram.org page on it. Could a sooty map sensor cause problems too?

 

The IAT is inexpensive enough to just replace it every 25K or so. I practically consider it a wear item! Just replace it when the MPG drops if you've ruled every other obvious thing out.

Checking resistance doesn't tell you anything if the sensor is good, unles you checked the resistance AT CERTAIN TEMPERATURES. If it has the right resistance at the right temps, then it's good.

The difference between 235 and 215 tires isn't enough to explain 4mpg, imo.

This one is kind of baffling.

I assume all the numbers you are giving us are hand calculated? It's well-known that bigger injectors will make the overhead read artificially high, and since your dad has bigger injectors than you do, it will make his overhead display higher MPG.

Heck, if I had an overhead in my truck, it would probably show 30mpg on the hwy!

 

Thanks Hohn, I probably will replace it anyway. The mileage figures are all hand calculated.

 

And a dually should do worse then a single rear wheel, and I don't think an HO usually gets better mileage.

I have the VanAaken, AFE air intake and 4" straight pipe.

I average a very consistent 16.8-17.5 on winter fuel.

About 13.5-15 during light towing.

Get around 19 MPG in summer though.

 

Assume you mean 75's ,...not 85's?
If so your 4% is correct. Can check it here...
http://www.sjdsm.com/tech/tire_size.htm

Did not see anyone mention Tire Pressure. Same as your dad's? Run em high for max mileage!

RJ

 

Your train horns are dragging you down Turn em around and blow em going down th road, you'll pick up 2mpg (j/k)

 

The tires are 85's. Tire pressures are the same as my Dad's. Looking at that website, the difference in the 2 sizes are 4.5%, not 4. Lol ten brooks, I never thought of that Thanks guys