I have a 2004 Tahoe Z71. From some reason my truck has started to burn/use gas like never before. I normally use my "Range" to determine how far I can drive. Of late, with only driving a 1/4 of a mile my range is dropping 2-5 miles if not more. One morning when I got to work, it literally dropped about 15 miles while in park. While my SES light was on, I got a code of PO442 which the guy at part store said it could be my gas cap, which is only about 1 yr old or some type of emission problem. Now to back up a couple of months, I have noticed a leak from the front of my engine. From what I can tell it is only anti-freeze. Definitely not an oil leak. Not sure if this is related to my gas problem or not. The truck itself is not hard to start, it's running as normal. No high or low RPMs, no loss of HP, not mis-firing. Any ideas?
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The range setting is not accurate. It is an estimate based on the position of the fuel level sensor, TPS, RPM, and speed sensors and the weight of the tank. It estimates high during highway driving and low during city driving. You can sit there in park idling for an hour and it will be different from when you entered the car.

The rest is indeterminable because we dont know the route you take to work, or how you drive. If you take the local highway mpgs may drop because of different speeds you use to travel to work or even impediments on the route which make your speed inconsistent.

Plus in the winter mpgs are lower because of the colder air that enters the intake is more dense than warmer air you would experience in the hotter months.

 

Majority of my route is highway. While on the highway is where I am seeing the drop in the range. It also continues to drop while riding on local roads. Now the funny part about this is I removed the neg cable to clear the SES light. Range did not change however the noticeable drop in range stop for a couple of days or so. Now the range is dropping and adding by 15 randomly. It doesn't seem to matter if I'm on the highway or local roads for this change to happen. I drive 40 miles one way to work. The other morning my range said I could only go 47 miles so I stop at gas station to fill up. It took 22 gallons to fill it up. I also added some B12 at the recommendation of the part store guy. I normally use mid grade but this time I used the 93 octane. Initially the range read 383 after fill-up. Drove roughly 1/2 mile on local road and it dropped to 380. Then I drove 25 miles on highway and miles rose from 380 to 394. Local temp here lately has been around 22 - 33. After work drove home 40 miles, by the time i got home truck said I could 401. This morning I got up range read 384. By the time I got to work it read 374. So at this point, I'm sure if B12 is the greatest product in the world or not. I'm just afraid I'm getting false readings and maybe possibly find myself onside on needing a gas can. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>

 

I dont think you need B12 nor high grade gas. It is just the way you drive. I dont think you have a problem at all.

 

I'll be sure to keep you update. Thanks for reviewing my problem. Very much appreciated.

 

The B12 won't make any major OMG! improvement in your mpg, but it will help clean up some of the carbon and will help the vehicle run smoother.

As RacerX pointed out it is colder and you are likely to be using more fuel because of that, the best way to verify any change in mpg is to track your mpg tank by tank, and keep a record of it over a period of time....

If your vehicle has the avg. mpg reading you can use that or hand calculate it, some will say the the vehicle calculation is not as accurate as hand calculation, but use one method or the other as they will both be consistent enough for you to get a idea of fuel usage.

If you use the vehicle calculation be sure to clear it at every fill up...

 

Thanks in2pro! Much appreciated.

 

As Jeff said, the sure way is to hand calculate your mpg. In fact it's a good practice to do anyway so you have a database to see it something is happening. Oh and BTW, stop when the nozzle clicks off unless it's obviously not close to full. Don't keep going to the next round number.

If you think the B12 did some good, run some Techron thru it.

Now for the cold weather thingy, the mpg goes down for several reasons. All the lubes are a lot stiffer, the engine doesn't warmup as fast, and some tend to make shorter trips in the winter. The cold, denser air actually is better (see CAI kits) and the computer keeps the A/F ratio fairly constant from the feedback it gets from the O2 sensors when it goes closed-loop.

My friend's 427 Corvette that we had tuned a little rich in the summer would run like a striped a$$ ape in the winter.

 

I don't use my range, I barely drive, just a few miles back and forth to work. I just had front and rear transmission seals replaced rear engine seal, water pump, serpentine belt, all new plugs and wires. 2WD 8 cylinders (Z) Why all of a sudden would it burn twice as much fuel? I didn't even know I had any problems until Tran started leaking.