Poor MPG, Stumped
 

Hey guy's so here's whats up. My 2000 wit 89K on it has been getting terrible gas mileage over the last month or so. I'm talking in the range of 11-13 with a mix of city and highway driving.

About 15K miles ago, I changed all the plugs, fuel filter, and air filter. About 3 days ago I cleaned the MAF sensor and the EGR valve. I can't seem to figure out why mileage has been terrible.

I've even been under the truck looking for leaks and checked the transfer case and front axle to make sure there is no problem there (replaced that vacuum switch on the t-case about 25K miles ago, it was stuck and causing my mileage to stink)

Anyone else got any idea's on what I can check?

oxygen sensor?

I thought of that... No Code though to tell

my blazer gets that, its because its cold out you're going to see worse gas millage when its cold out. blazers don't see much over 15 mpg's unless you drive like an old man

It has never done this before though, normally in the winter it runs about 14-15 even with some 4WD, and it was weird because it got the normal MPG that I'm used to, and then it randomly started getting poor mileage over the past 3 tanks

Thats always a tough one when no codes are thrown.
With what you have done already is a good start. Only other things you can possibly check would be.
tire pressure (which is a duh), fluid levels. Other than that your starting to get to the end of things where codes would or would not be thrown, such as temp sensor, o2 sensors, and your cat plugging up. It is difficult but sometimes these things will start to malfunction but not throw codes, there might be some other threads here about how to check /bypass/eliminate some of these

Yea, tire pressure was one of the first things I checked. I think I may try the wires and the cap and rotor since they weren't replaced when we did the plugs... I don't want to try the "shotgun" approach. I just don't know :-\

if its not running to rough it might be a long shot, but you can check the cat by checking the back pressure. I would try the cap and rotor before wires. I burn up cap and rotors, i think i run through about 2 or 3 of them every 100,000km

ANOTHER THING you can/should check is your rear brakes!, dont know how this one skipped me. I HAD this problem before, for me it was the rear passenger. the caliper was not releasing properly and the brake was riding the whole time.....easy check is go for a highway drive then feel all the wheels and see if one is hotter than the other. or take the wheels and calipers off and inspect the sliders/pistons/pads.......I figured it was this problem after a) i blew up a pad. and b) on the highway i drove from edmonton to winnipeg without using my brakes once!......i downshifted with the tranny and coasted into stops and gas stations and saw the gas mileage slowly improve.

hmmm what kind of mileage were u getting before this serious sudden drop?

i'm pulling an avg of around 17.5 mpg in my 97 jimmy slt with 280,000km's or 174,000miles PURE stock on winter tires - and avg temp here has been around 20's f or -5 c or colder (recently much colder) could your intake be blocked off or the filter clogged already?

Just a couple of thoughts.
Is your Blazer garage kept?
Do you fill up the gas tank at the same place?
Which octane to you use?
What kind of engine oil are you using?
I watch my rpm's more than I watch my speed.
And yes I drive like an old man especially during
winter time. 15mpg city 21-23 highway. Light on the pedal.

Mark