When it was in the shop they were only replacing one injector at a time and by the third time my dad demanded that they all be replaced. That is when it went from 12.5 to 9.25mpg.

 

interesting[:-] now i wonder if its even worth doing it? me and you dad seen to have alot in commen with the truck, if i go ahead and do the injectors i would be in same shoes with the 9.25....

 

I don't even look at the lie-o-meter any more. When I used to it was about 4 mpg off. The best I ever got was 17.5 on a 450 mile trip right AFTER an oil change, then back to 12-13 in about two tanks.

 

When trying to use MPG as a way to see if a Dodge pickup's engine is 'sick' in some way...it is always better to do a 100 mile or longer test at a steady 60 mph on a interstate highway.

Recently Trailer Life magazine did some 2005 to 2006 comparisons of Dodge Cummins Rams lightly loaded and if memory serves me right both were in the 19 MPG range.

Tank to tank MPG in mixed driving varies so much you can't use it to diagnose. If you floor your accelerator pedal and accelerate hard you will get 4 to 6 MPG. If you loaf along at 50 mph you will be over 20 MPG...so you can get MPG anywhere from 6 MPG to 20 MPG on healthy engines.

Spend the time and money to do a steady 60 mph MPG test...it is worth it.

I feel it is worth it to do a test like this every so many months just to catch problems early.

On a Cummins the boost gauge readings should be written down in a little notebook along with the MPG calculated by hand and what the overhead trip computer said, the outside air temperature, and a guess of what the wind speed was blowing that day compared to the direction the truck was going.

If your overhead trip computer MPG starts wildly varying with the hand calculation that is a potential warning signal that the fuel pressure is either dropping low or injector flow past a bad pintle is somehow going high....both things that should be further investigated.

It is also a good idea to use the stopwatch built into your cell phone to legally find the 40 mph to 70 mph all-out acceleration of your pickup on a level stretch of highway, and record this in the same notebook along with air temperature, and wind direction...with a note if the weight in the truck is much different than normal.

 

something is wrong with my truck then. because its a 2004.5 dodge ram 2500 quad cab 4X4 that i bought used. it has 190000 km on it now. My lie-o-meter constantly says between 23 mpg US and 27 mpg US. I drive empty at 70 mph when doing it. I slowed down and reset it and went 60 mph and it can read 27 mpg ish. is it hooped?

 

That is a good first step, to check the trip computer at a steady 60 mph for a short distance.

To really know if something is 'sick' you need to do a longer trip of about 100 miles or so...this is so you can calculate the MPG by hand and compare it to the trip computer.

If you can get more than a true 20 MPG calculated by hand at a steady 60 mph your Cummins engine is probably healthy, and at least in the 'normal' range.

If your 'well broken in' Cummins Ram with 190,000 km/117,800 miles
really is in the 25-29 MPG range on the highway
like the trip computer is indicating
with the torque converter clutch locked up
...it is actually better than average.

If the tank to tank MPG in mixed driving on city streets is below 10 MPG
then either the truck is being accelerated hard,
or is carrying a lot of weight in the bed,
or possibly the torque converter might be having some unusual problem
and is slipping a whole lot.

 

Someting has to be wrong. i always hand calc out my MPG and get 16 to 18 in city driving. i got 22 MPG on a 600 mile trip where i set the cruse control at 65 and left it there. this is in a 06 2500 auto with no load or trailer.

 

Does running ULSD make a difference? Seems like when I switched over for #2 I lost about 3 mpg.

 

does any1 elses lie-o-,eter read like mine? mine says 22-26 all the time on highway

 

The ULSD diesel fuel has hurt MPG on big 18 wheel truck fleets
where their careful records are showing
5-10% worse MPG since ULSD came in.

On the newest Cummins Rams burning ULSD
the MPG hit is probably worse
because of the backpressure of the particulate filter
and the 'burnoff' cycles to clear out carbon from the particulate filter.

I have heard mixed opinions about whether the heavier flow of cooled EGR gas on the new diesel engines is hurting fuel economy.