Bad Fuel Consumption Problem

[pwbum1]

I have a 2003 Z71 5.3 liter vortec. I just completed a road trip up I-95 my mpg was around 9-14 doing 80mph. I usualy get anywhere between 18-21mpg at the same speed. I had a garage check it out they changed the fuel filter which was dirty and scanned it for codes but nothing came up. His gut feeling was the computer was giving me wrong information on the inst econ reading. After that driving in town it reads 3-9 mpg. The mechanic said my psi was 50 a little low but wouldn't cause that big of drop in mpg. He said he could replace the fuel pump for about $6-800 but wasn't confident enough that was the problem to rip it out. Does anyon have any suggestions on what it could be?

 

[73shark]

Welcome to the Tahoe Forum. First thing I'd do is run two or three bottles of Techron thru it. Also I'd do the math on the mpg to verify the computer mpg. I've found that the computer is always a little optimistic on the GM vehicles I've owned.

Honestly I'm surprised w/ the 18-21 mpg @ 80 mph. Have you ever done the math on any of those trips?

 

[Sepiroth]

Depending on where you live, also you could be running winter blend fuels that do burn faster and have decreased fuel mileage.

 

[Ajay]

Depending on where you live, also you could be running winter blend fuels that do burn faster and have decreased fuel mileage.

Ethonal Blends will kill mileage

 

[johnebgoode]

Check air cleaner also. That will hurt your mileage too.