4X4 Problems on a '97 Blazer

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THere are no hubs to lock, jus a axle disconnect on one side of diff. If it was stuck engaged it would make maybe 1 mpg difference at most in that truck. If you have it jacked up with oversized rubber to I would say 12 to 15mpg is good as some get less. How you drive it too has some effect on MPG and in hot weather with A/C on a lot it will drop some too. ALso if it is hot and you are using 87 octane in that engine the DCM could be retarding spark a lot to control knock (you only hear it when it is so bad that ECM can no longer control it.) and this retarding can murder MPG and performace too.

Everything is stock on it. I will try the higher octane in it and see what that does. When I drove it to the airport last week, all highway at 65 mph, I burned half the tank going and the other half on the way back, about 190 miles total. I don't notice a big difference in town or on the highway. I gat about 190 miles per tank. I am going to pull the plugs this weekend and see what they look like. Would the ECM give a code if it is retarding too much? I have only gotten the o2 codes so far. Also, I assume that could have added to the o2 sensor code? It does have 120K on it anyhow. Thanks for the direction.

Just for an update. I have been away from home for the last two weeks and just got in last night. My wife told me that the Blazer had thrown another engine code. It was the front O2 sensor again. I just replaced them both so I don't figure the sensor is bad. I am going to check the condition of the plugs tonight. Anything else you guys think I should look at?

Try checking the connection on the front O2 sensor, its still possible that the o2 sensor is bad, especially if it was purchased at autozone, We got two for our 99 jimmy and they went bad within two months and I had to replace them again.