I have a 2001 Blazer LS 4x4 4dr. I am either getting horrible gas mileage or my gauge is screwed up. I topped off an 18 gallon tank, and drove 160 miles and my low fuel light came on because the gauge was on empty. I have no fuel leaks in the tank or lines, I am an amatuer mechanic and cannot figure this one out. Someone told me that this could be a sign of a bad fuel pump. Why would my gas gauge be doing this? If it is not a problem with the gauge, why am I getting such horrible gas mileage? I would greatly appreciate any novice or expert advice. Thanks.

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a bad fuel pump is a good possibility. Do you notice if your gas gauge jumps around alot? that is a good way to tell if its the pump

 

It doesnt so much jump while im driving.... It fluctuates really bad in neutral and park. The parking lot where I work is level and it was on half a tank when i went in work, when I came out from work and started it it was on 1/4. It confuses me. . . . I even run a K&N filter and a tornado fuel saver for better gas mileage, they worked at first... now i cant tell. . .

 

A very easy way to see if it is the gauge or the fuel mileage is to reset your trip meter when you fill up, then the next time you fill up, write down how much fuel you put in and how far you went. Divide the miles by the amount of fuel and you get your MPG.

The Tornado has been proven to be a farce and a waste of money. Car & Driver and Motortrend both did tests with just about all "fuel saving" devices sold and not a one of them actually worked. The tornado was one of them and in all of their tests it consistently got 0.3 mpg less.

One posibility is that the oil from your K&N filter has coated your MAF sensor, causing inaccurate readings, giving you poor mileage. CLICK HERE for a post I made awhile back on how to clean your MAF sensor. It may just restore your lost performance and economy.

Try cleaning your MAF and getting an accurate calculation of your fuel mileage and let us know.

 

I must have missed the article in Motor Trend, I have been a subscriber for 5 years and I wouldn't have bought the tornado had I seen it. I just put a brand new Mass Airflow Sensor in the truck. I will try to clean it anyways though. Thanks for the help.

 

If it's new, I don't know what it would help to clean it, but so long as you are careful, it shouldn't hurt anything. It shouldn't need to be cleaned with a q-tip. If you remember what the elements looked like when new (should have been almost white), that is what you want them to look like.

As always, when cleaning your MAF sensor, BE VERY CAREFUL! You know how much you paid for it. You don't want to spend that again if a mistake is made.

Also, when was the last time that an whole tune up was done (plugs, wires, cap/rotor)? Also, how many miles are on the vehicle? If you confirm that your mileage is down, it may be time to change the two upstream O2 sensors as they can get lazy and effect fuel mileage long before they actually get so bad that a DTC (diagnostic trouble code) is triggered.

 

my 99s10 does the same thing just changed plugs cap and wires has 101,ooo milesgas gauge does this only reading half tank or lessneedle goes crazy low fuel light comes on even though i know there is at least 6gallons in truck have been told this was the sending unit in tank was als told you can buy this from a parts store seperate from pump assembly an expensave gm part any input will help thanks steve.

 

Do what Kyle said and "track" your actual mileage first it sould be between 18 and 22 mpg give or take depending on your driving. A couple of quick checks that you can do to see if it is your fuel level sender (which is available seperately from the fuel pump assembly even from a dealer) is take it to autozone and have them scan for DTC's a faulty fuel level sensor will set at least 1 of 3 codes (P0461,P0462, or P0463) If one of these are set it is ALMOST always a faulty fuel level sensor, and these are type C DTC's which means they will not turn on the Service Engine Soon light. Also you can turn on the ignition and violently rock the vehicle back and forth while you are watching the fuel gauge usually if there is a dead spot in the sending unit this will cause the gauge to fluctuate badly and turn on the low fuel light.