I just bought a '01 2500 with 117,000 miles, 5.9L 24 Valve Cummins Turbo Diesel, Automatic 4sp w/ electronic overdrive, 4x4, Quad Cab, SWB, SLT Lariat. *3.55 axle ratio', that truly is in excellent condition. Everything is stock except the Increased capacity Air filter and the tires now (285/75/16) rather then 245/75/16 which were the stock tire size. I have the complete service and mpg history and it went down from 16.0 city mpg on the 10,000 miles before the tire change to 14.8 mpg city During the 10,000 miles after the larger tires were put on. Over the past few tanks, I have been getting 16.5 mpg with empty, no towing, highway driving. I want to see what the best fuel economy possible is so I keep it as close to 1500 rpms as possible. although I live at high altitudes (8000 ft) all of my driving over the past few tanks have been over nearly flat roads. I have a couple of friends whose nearly identical trucks with more miles (rough ranch/farm miles at that) get 20+ easily, but they can't tell me why. Any ideas? Most of it's "life" was spent in Texas with city driving and I bought it from a guy who just moved back to Colorado from Houston. If I can't get it to 20 highway I'm going to have to sell it and it's too
beautiful of a truck to do that without trying to figure this out.

Thanks

 

Has the speedo been recailbrated for those tires?
Next, is there fuel pressure at the injection pump? If not, or it is low the injection pump may be damaged.
These trucks must have a fuel pressure guage inside so you know what is going on. Does it clatter like other 02's? Maybe the injectors ar in need of service.
many other things to look at.

 

try cleaning the intake air temp sensor or replace it. if it gets dirty it will lie to the computer<I just changed mine it was getting 17mpg now its back over 22 mpg

 

The Gen 1 Cummins got the best over all mileage at 15-1600 rpm.
The Gen 2 Cummins gets the best over all mileage at 18-1900 rpm.
The stick shift gets slightly better mileage than an automatic, depending.
Tire pressure at the max gets the best mileage you can get.
I've only gotten 20 mpg one time. The average with no load is 17-19 mpg.
With the camper on, driving @ 62 mph, I get 15 mpg on the flat. (10,000 lbs. gross) Not on the flat:

I"m getting up enough in mileage on the motor to change the injector pump to the Fedex pump, which is supposed to increase mpg and power at the same time. No wire for me.
regards, as always, jefe

 

I had similar problems when I bought my truck 3 years ago, and now with time I've worked out all of the kinks and am getting around 14-17 city, and high teens-low 20's unloaded, on the highway on a consitent basis. The most important thing is to not give up, have patience and learn your new truck. I've noticed that after a slump of poor fuel economy, if I keep my EGT's higher in the 1000-1100 range, with either a canyon drive or tow the car hauler/or boat out to WY or to CO, once I get back I immediately get better mileage unloaded for an extended period of time, usually 3-4 full tanks of diesel. With daily, unloaded driving, to and from work, I realized that my truck hardly gets up high enough into the EGT's, usually not getting above 800-900 degrees, to actually properly heat up and create optimum operating efficiency. These trucks are really cold blooded and can take a good while to heat up properly, so the best thing to do is to make sure you stretch its legs once every few weeks and make it work to keep things running well. Something else that helped me out as well, is installing an Edge J/A module and exhaust, from this alone I picked up about 2MPG in all conditions, loaded or not. Anyhow, regardless of the aftermarket electronics, the main point is I that using these trucks once in a while for more than daily driving will in effect render better fuel mileage.

 

Thanks for all the suggestions, I'starting with going back to smaller tires and a fuel gauge pump. Also, you're right, the best milage comes after driving it for a good distance, the further the better. Tires needed changing, winter is coming and all my friends who have had aggressive mud 285's in the past hated them in the snow and went back down in size and tread.

 

Hey rebel, where is the air intake temp sensor?

 

JEFE has it right. At 1500 RPMs you are lugging the engine and not at its best point for efficiency. 1600 to 2000 is pretty much the sweet spot on the 24v.

Reference: Robert Patton's TDR article "Its about the fuel economy stupid"
http://www.turbodieselregister.com/t...ueleconomy.htm

 

Tom,
After rereading your original post, I notice that you have not replaced the lift pump. You need to upgrade the lift pump and go to a big line kit. Right now. It is the one single thing that will make your rig go south in a hurry. There are a lot of fixes for the orig. lift pump. Do a little research on 'lift pump' on here and you will get an education, ... and a long liturgy of despair.
regards, as always, jefe

 

That isn't bad mileage for around town.

Try: Cleaning your IAT sensor
Adding a lubricity/cetane booster to your fuel
Hand calculating your mileage
Calibrating your speedo/larger tires throw it off
Checking mileage on summer blend fuel(winter blend is starting to show up in the hills)
Returning to a stock size tire of highway tread design and running them at factory recommended air pressure.
Calculate true mpg on a longer run trip to see what it is capable of.
Make sure your trans isn't slipping.
Don't believe everything you hear about high mpg trucks, you can expect around 20 highway from a stocker and can be **** proud of it. After all its a 3.5 ton truck empty!!

 

I checked the milage with a GPS and am actually running 9.65 miles for every 10 my odometer is reading, also I aways hand check the mlage, and computer is only about .2 mpg off. Was going to go back to stock tires (245 75 16) but a friend suggested 235 85 16, they look good on his truck. The lifters will be modified quickly, already heard the horror stories.. Where is the IAT sensor located? lastly, what are the pros/cons of straightening out exhaust pipe?

 

The IAT is at the back of the head/drivers side. Takes a deep13/16" IIRC. Use electrical parts cleaner only or you will fubar it.

An aftermarket 4" exhaust, turbo back with muffler helps lower the egt's substantially and is a good bargain for starting a power build up. I have had an aluminized MBRP for over 5 years now and it is showing no signs of corrosion or wear.

 

http://mopar.mopar1973man.com/cummin...map-sensor.htm