My first 4 full tanks of gas in my rodeo varied from 16.5-17.5 depending on how hard I drove it. Then my alternator died and me and my dad pulled it out, had it rebuild, and reinstalled it.

Since then I have ran out of gas on the side of the road twice. The first time at 286 miles (13.6 mpg).

And yesterday I ran out again at 297 miles (14.1 mpg).

In between those too I filled up the tank completely at about 200 miles, but did not work out my mpgs for that tank.

I really dont know what could be causing this horrible milage and whatever it was happened between the alternator dying and getting fixed. I was thinking that maybe we could have knocked the timing off in the engine or hit the distributer, but really have no idea. It may have nothing to do with the alternators installation and maybe something else that coincidently started to mess up at the same time. Maybe I have a dead cylinder? I have not noticed any loss of power although I don't really have a means in which to accurately measure it and I have also been driving as conservatively as ever so that is also not the problem.

Any help is greatly appreciated.
Thanks!

Just a shot in the dark. As your alternator was dying your electrical system would have been down on power, this might have led to a weak spark, and finally, build up on the plugs. Probably too easy, but you may want to pull your spark plugs and have a look.

If you find the distributor or a way to adjust the timing, you have more problems than bad gas mileage. <img src="/forums/images/graemlins/smile.gif" alt="" /> I can assure you that you did not bump the distributor.

If you did not do it when the alt was replaced, disconnect the battery for a while. It may help reset the computer. Other than that, start looking the usual problems. Bad fuel filter, dirty air filter ect. If that does not turn up something, then get the codes scanned and see what the computer has to say. It may be as simple as a bad O2 sensor.

Good Luck,
Michael

Like Michael suggests, look at the easy stuff first- make sure your tires are aired up, replace the air filter. 14-16mpg is pretty typical for a stock 1998+ 3.2 4x4 w/ AT, that's not doing straight hywy driving. One of your pre cat O2 sensors may be on it's way out, but not totally failed, as to set of a CEL. If you have over 100Kmi, it's not a bad idea to replace those two O2 sensors. Any major malfunctions with this truck will light up the CEL. G/luck
Joel