~30% MPG drop after better driving habits
 

Alright so I joined this forum in hopes to find a way to get my 2000 Chevy Blazer to stop chugging gas like a frat boy drinks keystone. I've seen the success stories, read the tips, looked at the possible mods, etc.

I recently refueled and for this entire tank have kept the vehicle under 2k RPMs (got a lot of honks though), stopped hitting my brakes as hard, popped it into neutral at every light and released the brakes while on flat surfaces, haven't let the engine stop the car when backing out of the drive way, took my roof rack off, and I'm sure maybe some other things that I'm not recalling right now. Basically, I've stopped driving like a 22 year old guy normally drives.

Since my last refuel, I've driven 150 miles and I'm at empty now. Usually I will get anywhere from 220-260. So how the hell is this happening? I recognize that something could be wrong with it, but there's no check engine lights going, it sounds great, and hasn't been acting up.

I went from 15.5 - 17.5 mpg to about 10. What in the world do I do about this?

Automatic? If you're always accelerating at under 2,000 rpm, it may be that the torque converter never locks up, giving you horrid gas mileage.

That's a big drop while trying to do the right thing. :(

I've had unexplained "bad" tanks and only later realised that I mustn't have filled the tank completely at the start, or maybe overfilled when refilling.

Your post seems to say that you haven't actually filled the tank yet. Maybe your fuel gauge is playing up?
Lately, my fuel gauge drops like a rock, but when refilling, I find it's still a long way from actually empty.

Anyway, I hope it's nothing serious. ;)

More than often because of my highway driving routes I'm using cruise control that holds it at 65mph and 1700-1800 RPMs. I didn't think about the torque converter at all.

So the quicker I can get the torque converter to lock the better gas mileage? Sweet! I get to floor it everywhere!!

Well, maybe not floor it, but brisk acceleration in an of itself won't hurt mileage. Unless you end up doing it right before another red.

I will keep this in mind on my next tank. I felt like such a douche accelerating so slowly anyways.

Get an OBD2 tool like ScanGauge, that will tell you what's happening when.

Yes, get a ScanGauge or maybe an UltraGauge.

Do find out what really controls torque converter lockup.
I've read it's determined by road speed but there's no guarantee that's correct.
I do think it only locks up in top gear, or maybe in the top two gears.

Do you want to chase down the lockup solenoid cable and have it run a light on your dash?

agreed with above the reason older autos are considered worse then manuals is because you have to use the torque converter to get better mileage when accelerating. The torque converter is basically controlling the transmission like a manual still not as efficient though. This is why normal people think modern autos are better than manuals due to the torque converter locking up more often than older ones.

I find on my '02 grand am it is much much easier to lock up the torque converter in top gear and only after the transmission has warmed up. I can get it to lock up in lower gears but its much harder to do

A step back to go forward? Too slow of acceleration (as other have said) will use more fuel, try 2.2K to 2.3K in first and second. Again without instantaneous MPG read out your are just guessing, get some kind of gauge and keep a fuel log. I haven found putting it in neutral at lights to be much of a fuel saver, however no AC and shutting it off do.

On a heavy vehicle a key point is when you lift and coast length. Up your tire pressure if you haven't. What type of commute or driving do you do? If you do much city driving the lights and timing my not allow you to reach the speed limit between lights before you need to back out.

Let us know what works for you.

Good luck.