I have a 2005 extended cab silverado, with 3.90s and 265/70/17's, and I noticed I'm getting terrible gas milage. I filled up with a full tank on thursday night, and last night I had to fill up again because I was at empty after driving only approx 250 miles. Usually I get anywhere from 325 miles on up per gallon.

Does anyone have any ideas on why the mpg dropped? Would seafoam help? Howabout a clogged fuel filter? I have a custom tune; could I be running rich? I also have yet to do the crank relearn sequence, could that be affecting the mpg as well?

I always keep my tires properly inflated, and I generally do not drive faster than 70-75 mph...

I appreciate any help!!

 

it's probably just your driving style/driving conditions. do you drive city a lot? 75 miles is a big jump though. coulda been some bad gas. if it continues i'd have it looked at

 

I drive an equal amount of city and highway, and its been happening for awhile now. I don't quite know what to make of it.

A friend suggested that it was the lift I put on, but that still doesn't make sense to me. My pickup sits about an inch higher than a z71, so the lift was nothing drastic, and like you said, 75 miles is a big jump.

 

well are you running the stock sized tires or larger?

if you have gotten bigger tires and haven't changed the PCM to realize that you have larger tires, the odometer will read a shorter distance than actually traveled.

if your stock tires were 29's and you went to 33's. you travel 1.14 times more distance than with the 29's, meaning your "250" miles really is more like 285. which 35 miles will make a difference.
lemme know the specs of your lift/tires. i'll try and find it in your cardomain page

 

check your tune
winter blend gas takes a good chunk out
check for exhuast leaks
clean your maf

a clogged fuel filter shouldn't effect MPG, just performance as far as I can see.

 

I have never experienced this much drop with "winter blend" gas. Really, I have never experienced any drop.

I will check for exhaust leaks... but how do I go about doing that?

I have a large suspicion that my tune has something to do with this, but I have gotten the PCM adjusted to my tire specifications, so everything as far as that is concerned is fine. Btw, the lift is a 4" spindle lift.

 

[QUOTE=4.8 Liter Of Cola]
I will check for exhaust leaks... but how do I go about doing that?

start your truck and hold your hand against the end of the tail pipe....if it pushes your hand away then you have no leaks.....

 

your truck, doesnt really have a serviceable fuel filter.. its in the tank.

 

yep on the bottom of the pump right? Thanks GM

 

I had forgotten about that....