2001 diesel, 34,000 miles. I towed a 3,500 lb. trailer about three hundred miles on a relatively flat surface and was surprised to only get 11 mpg. I bought this truck because my old suburban only got 11 mpg. Would you folks comment on what might be causing what I think is poor mileage.?
Thank you

 

auto or stick
sicks get better mpg
do you have any mods or is the truck stock, try changing the fuel fiter or changing trans. and diff oil

 

I don't know much about the 2nd Gen Diesels, or other Diesels, as many of the people on this site but if it only has about 34,000 miles your not going to get very good milage because you need to break the engine in. Milage will drop even more with low miles on your engine because its under load. A rough estimate for engine break in is 100k miles. But keep in mind that each engine is different and may break in at a different milage. They also break in faster if you tow with them a lot simply because there is more weight and more load on the engine so it could break in as much as 20k miles sooner. Once you break the engine in you will see an improvement in your milage. I hope this helps. Sorry if any of my information is incorrect.

 

You should be getting much better milage than that - a Cummins shouldnt even feel that kind of load. Theres lots of things that it could be:

Dirty fuel filter, dirty air filter, pickup issues in the tank module, air leaks in the fuel system, lack of fuel pressure, unhealthy VP-44, brakes dragging , torque converter or other transmission issues, etc. etc.

Arne, please spend some time reading the second gen forums to find out about the importance of guages, and in particular a fuel pressure guage.


EDIT, I did not catch the mileage - mileage will likely improve you are a long way from being broke in

 

First thing, kudos on finding a practically brand new 01. 2nd, add an Edge EZ, and you should pick up 3-5 MPG.

 

Also, I moved this thread cause this is not an urgent situation.

 

Check your fuel filter. Get yourself a good set of gauge such as Boost, Pyro and Fuel Pressure.

 

Arne - I returned your PM. Please read the stuff about a fuel pressure gauge carefully.

 

11mpg, lots of possible issues.

Were you towing a building? Wind resistance can account for huge variations when towing.

Also, speed and gearing make a huge difference.

But most likely culprit, dead lift pump.

As mentioned above, check the fuel pressure first, replace fuel filter.
Pull and clean MAP and IAT. Use brake cleaner, do NOT use carb cleaner.

And a plug in box will net a few more MPG, however, you are far too low for my likes.

As far as stick/ vs auto and mileage, when the auto is locked up, it's like driving a stick. I get over 24MPG and make over 650HP.

Dave

 

As stated above, gearing and speed can make all the difference. How fast were you driving and what is the axle ratio of your truck? Axle ratios can be found either on a sticker on the underside of the hood on inside the glove box door.