10mpg 2001, no codes, no smoke runs smooth

Ok my Girlfriends 2001 blazer is in great shape, was getting 19mpg give or take a mile here or there. Just after Christmas it started getting about 13mpg. I checked everything, pulled the plugs they all look great, air cleaner fine,5w-10w oil fine. no brake issues. No smoke out of the exhuast, runs great, shifts fine, everything works except the gas guage its sort of eradic.
I took it to the Chevorlet dealership here in Alice,tx and told them that its getting horible milage. That afternoon go to pick it up and they say they cant find anything wrong with it only that there was a code for high voltage to the fuel sending unit there for the eradic readings on the fuel guage other than that the guy ask if I was calculating the milage right?
So paid the bill $122.00 and still wondering:crying:
So I thought well maybe it needs to be put under a load to blow out some carbon. So normally I tow a 1ft trailer with a L4400 tractor on it with my 1992 blazer and with that wieght (4400lbs) I get about 14 mpg with it. Oh it has 124,000 on it, My 92 about 290,000
So I had hers this weekend and 132 miles It took 15.5 gallons.:banghead:
I pulled fine no odd sounds or smoke or power issues. It would stay in a lower gear most of the time, my 92 would be in OD.

Im open to suggestions on where to look next, the vehicle is 100% stock just cant figure why the sudden lost in mpg. I would think it would be hesitating, or stalling , smoking somthing:jerking::jerking:

Is the SES light on? If so, did you retrieve the Diagnostic Trouble Codes, (DTC's)?

transfer case in 4Hi?

It would stay in a lower gear most of the time, my 92 would be in OD.



This is the only thing I see that throws a red flag. Being in a lower gear wouldn't account for the bad reduction in mpg you are seeing. Possibly whatever is causing the low gear is also causing the low mpg. It is that the throttle plate is open further of course, but why? IDK.

How about doing a vacuum test at constant high speed in OD with convertor locked up in both vehicles?
How about doing a timing advance test at same conditions? (flat ground)

Another thing seems to be occuring too: it is getting worse which means easier to find soon. :frown:

Any possibility of an odometer issue?

did you check the gap on your plugs? a dirty air filter will also do this. and are you using ac's for a plug? and don't rual out the cat getting cloged aslo sounds out of time unless it's the cat. and don't forget don't put air in your tires that they say on tire go buy what they want to run air pressure look on the sticker on door or owners maual you will get more milage per gal on gas with right air pressure.

Not much has change no codes at all had the GM Dealership check it again, They thought it was stuck in 4HI but it wasnt, Double checked air cleaner, fuel filter, tire pressure. Got 15 out of it last week but thats it, And thats driving 27 miles at 60mph no traffic lights , only 3 stop signs by my work takes about 35 minutes to get here. My 1992 blazer gets 21/23 at 60-65mph. Oh thought it might have been possibly AC compressor hanging up but havnt ran the AC the last two weeks its been pretty cool out.

High voltages are generally a symptom of bad grounds. If the ground is bad, the device will pull more voltage to try to operate.

There is some drag on the engine to drop the mileage that badly. Anything that far out of spec would seem to be soon to fail.

My torque converter lockup solenoid went out and killed the gas mileage, but that sets a code.