First of all, I'll have to apologize for bad english - I'm from Norway..

Anyways, my 2001 2500 LT 8.1 has a really bad mpg.
I just drove about 435 miles on highway down to Germany, driving at an average of 75 mph.
The result? 53 US Gallon, which should give 8,2 mpg
When driving in the city/mixed driving, I get 7,8 mpg
As a sidenote, a gallon cost slightly more than $10 in Norway, so I rather see it fixed soon...

Something has to be wrong, even though it's an 8.1 engine.

In addition, when idle, it runs a bit unstable - although the rpm is steady.

It also throws out quite a bit smoke from the exhaust. However, it doesn't lose coolant.

Do you guys have any advice regarding these problems?
Please, if you can, name the spare parts you recommend by make and model.
That would make it a lot easier for me to order, giving the fact that I have to order through eBay or US stores.
There's not too many stores here in Norway selling parts for these cars, as a new 2014 Suburban cost almost $300 000

Thank you very much for any advice!

 

How many miles on it? When was the last time it was tuned up? Is the check engine light on?

I'd start with the basics - plugs, wires, air filter, fuel injector cleaner, etc.

Then I'd move on to things like the Mass Airflow Sensor and Oxygen sensor.

 

Hi, and thanks for your reply.

It has about 169 000 miles on it.

My biggest concern. however, is that we only have access to 95 octane gas, not 87 or 89 as it's recommended here in the forum.

Regarding spark plugs and wires, is there any brand that is recommended?
I've been looking at plug wires with 10.2 mm and more.
However, it looks like it's recommended with 8.5 mm only.
Some say that thicker plug wires will grant a better fuel economy.

 

I would also clean the IAC valve (Idle Air Control), and the EGR with a carb cleaner. If they are both clogged it can affect the idle speed and the fuel effeciency.

 

is this a new vehicle for you? if not, has the mileage gone down recently or has it always been around 8mpg? as i just posted in another thread, my 2001 6.0 just got 9.3mpg for a tank so you're not too far off from that. I would try and find out why its smoking so much though before putting parts in it.

 

See if you can get a hold of Chevron injector cleaner or RXP cleaner... Not seafoam.

Check compression while changing out plugs and wires.