2005 GMC SIERRA 4.8

JZavala · March 10, 2020

Good day to all of you GM TRUCK owners,

I have 2005 Sierra with the 4.8L engine. Recently I've started to pay attention to my gas consumption and noticed that my truck goes thru a tank of gas in a matter of a week. It runs very smooth, it doesn't sputter/misfire, it has 200+ miles on the odometer, and recently I added a cold air intake. The tailpipe is covered in soot (BLACK SEDIMENT). Could this be a situation where the truck is running too rich? if so, any of ya'll have suggestion on how to improve the gas mileage. Thanks in advance

CamGTP · March 10, 2020

Well you gave a poor explanation of your issue.

A tank of fuel per week does not tell me jack squat about actual fuel mileage. I could floor my truck all day from stop light to stop light and the tank would last 3-4 days at 3 miles per gallon doing that. Or I could drive it calmly at 70mph get 22mpg and over 400 miles of range. Then if my weekly commute was 380 mile per week, that would make it last me all week.

You get where I'm coming from now?

So you tank of fuel is lasting you 1 week. How many miles are you covering in this week? What is your hand calculated fuel mileage?

What king of maintenance have you done to the truck?

If you have a hand held scan tool you could watch what the engine is doing. If you knew how to read the tool and understand the data, you'd want to look at fuel trims. If the long term and short term trims are extremely negative, the engine would be using more fuel than really needed and is having to remove fuel on it's own to make it happier. A loss in mileage may be noticed from this.

And soot or black in the tail pipe is pretty normal. It's going to happen on a gas engine like these. If it's spewing black smoke, that is a different story.