Well I just bought a 2004 2 door 4.3 ltr Blazer last month that has an automatic transmission with 26k miles on it. After the first week, I noticed I was getting horrible gas mileage so I filled the tank a couple of times, tracked exact miles, divided by how many gallons I put in and the result is my car gets 10.7 mpg - far below the 16/19 miles as stated. Now I know this topic has been addressed before, but I haven't seen anyone with this low of gas mileage, especially on a car that is practically brand new. My question is, besides the front axle not disingaging (which isn't my problem - I checked) and 02 sensors, could the previous owner have changed any settings to improve performance but ruined the efficiency? I know this truck was used for towing so maybe he set it up for more power? If so, how can I check for this, or could it be another problem?

Any help would be greatly appreciated cause this is killing me.

Thanks!

 

You could have diagnostics ran on the auto. It's a 4.3 liter and automatic so it's bound to be a gas hog.

It's a 2004 with only 26k on it. Sounds like you may have found out why the previous owner was selling it. He couldn't afford the gas. However, there are a few things I would do to improve the performance and gas mileage issue.

The first thing I would do is a full service tune up. You may surprised by how much this gets overlooked and how many gremlins letting this pass can cause your auto to have. From the plugs to the air filter. Full service. Your plugs not being gapped propperly could cause it to suck gas just like a nasty air filter will.

Last but not least. Run your tank as close to E as you can stand it. Get 1 qt. of automatic tranny fluid and a funnel. Insert this 1 qt. into the close to empty gas tank. Fill up with premium. Now this only works if your'e fuel injected and I am sure you are.

What the tranny fluid in the gas tank does is makes you 2 cycle. It's going to clean **** out of the injectors as well as lubricate the entire system. But the beautifull thing is with the addition of premium gas to this equation. Your engine will burn more hot than normal, clean out engine gunk or residue of any kind. Lubricate your internals, make you run more smooth, it also improves gas mileage.

I do this to all of my auto's. If you nut up and try this 1 tactic after you have everything worked out, you'll not only be thanking me, but you will pass it on as well.

Good Luck

 

I'm gettin 13 in heavy traffic and 18..... in the 80 miles hwy. I believe the figures are correct for the 2000 4 doors, 4.3 auto.
Suggested: 195º thermostat (maybe is clogged open or too low in temperature: more fuel to heat it up), check the rad fan always on (carefully, mechanical effort and lo temp)), a vacuum leak somewhere (poor gas air ratio and the PCM is trying to fix that), the MAF wires dirty... and your right foot.

 

Could you tell me how high octane gas will burn hotter?

 

I've never in my life heard of putting a quart of tranny fluid as a fuel injector cleaner. Can anyone back this up? I would try seafoam through the intake and in the gas tank. It worked very slightly for me, but it was better than nothing. I still get 10mpg on my 92 4.3l Vortec

 

Please lets not get off topic here. The topic is trying to help the author find the reason behind his low fuel mileage.

I know on my truck, it is finicky about where I get gas. It absolutely hates fuel from the local Walmart (can't think of the brand right now) and it will drop 4mpg just using that fuel. Fill up at either the local Mobil or at the new Kinney station and I gain that mileage right back. So maybe try a few tanks from a different gas station and see how it reacts.

As a start, I would also like to recommend that you try some Iso Heat in the tank to check and see if maybe you have gotten some water into the tank that is causing issues. Run it through a few tanks.

I would check over all of the ignition components. At only 26k miles, there should be nothing wrong with any of these components, but manufacturing as it is these days, it could have been a factory flaw. The wires can be checked at night with a spray bottle of water. Just mist down the wires and surrounding surfaces and look for sparks jumping around. I would also pull the plugs to check their condition and verify the gap.

Check/replace the air filter. If the previous owner had installed a K&N or other oiled aftermarket air filter, the oil could have coated the MAF sensor, causing all sorts of issues, one of which is poor fuel mileage. You would want to clean the MAF sensor (run a search, it has been discussed before).

Now, I have never heard of putting auto trans fluid into the gas and would highly suggest you do not. With the plethora of quality injector cleaners on the market (Chevron w/ Techron is what I use on a routine basis), why go with such an unknown.

Higher octane does not mean higher combustion temperatures. Higher octane simply means that a fuel can withstand higher pressures before spontaneous combustion occurs (pre-detonation). The content of say ethanol in the fuel will mean higher combustion temperatures due to the burning properties of ethanol vs gasoline. And ethanol is a very good cleaner of fuel systems. That is primarily where it gets its bad rep from. It will clean a fuel system well enough that the first few tank fulls may result in very poor mileage, however, it is just the varnish that was left behind by gasoline that is being dissolved by the ethanol that causes this. But again, that is a topic for another thread.

But before you do any of this, get some input from the dealership you purchased it from and explain to them that it is not running properly. 10mpg is not proper. At close to 3 years old and less than 36k miles, it should still be under the GM warranty.

 

Thanks for all of the suggestions. After doing some more searches on this forum and seeing that I'm way off target, I made an appointment with the dealer for Wednesday - thankfullly, I purchased the GM extended warrenty. I'm also going to pop the hood tonight and see if I have a K&N filter & check the MAF Sensor.

As a side note, I've been filling the truck only with Mobile or Hess 87 octane and the results are the same. I'll re-post as soon as I find or get an answer. I just hope they don't give me the runaround that everything is fine and try to send me on my way.

Thanks!

 

Cleaning the gunk out of your injectors unrestricts them and allows them to work propperly. With an MSD dist cap and wires and iridium plugs, it just burns more hot. 92 octane burns more hot than 87.
Once you fine tune your combustion times with your spark times and your gas to air ratio, this is what I mean by hot. I don't really mean combustion temps. Sorry for the slang on my part.

As for the tranny fluid. Try it. The smoke you see is the carbon and other residue being burnt off. Run the tank half way down and refuel. With premium, you can use 87 oct. and still feel it working. But the premium sets it off. I tried sea foam in the gas tank. it was alright, but the tranny fluid costs less and works better. I tried marvel mystery oil in a pich on a otr trip. It was about the same as sea foam.

Some of you chevy guys think different than the crowed I am used to. But that's cool. I can dig it if you cats can.

 

it also might be possible that the guy before put lower gears in you said he used it for towing. that will keep your gas mileage down no matter what you do. just another idea.

 

Very good point about the gears. What are the tell tale signs if they were changed? Lower RPMs?