Well last Sunday (March 21st) I decided to top off my 1994 S15 Jimmy 4-door 4x4 with the 4.3 Vortec CPI with 87 octane fuel. That cost me almost 45 bucks and the tank wasn't even empty. So I thought that I better start driving a little more carefully to save gas and I did. I made a habit of accelerating gently, to the point where I was always the last one out of the red light by far, and I didn't let the rpms get very high at all (my truck doesn't have a tach so I was going by ear lol). And the second the speedo would hit 45 mph, I'd let off the gas to coax the transmission into shifting to overdrive. So that tank lasted me exactly a week. The gauge read empty on Sunday a couple days ago, and I drove it like that for a little while, to the point the engine would stall on firmer stops. The range I got was just around 250 miles on that tank before I burned another 20 bucks on gas.

So considering that I have an 18 gallon tank (thats what I read on this board), 250 miles divided by 18 gallons equals... 13.8 mpg. WTF?! The EPA rates my truck at 15 city/20 highway.

I drive in mixed conditions, but mostly around town so that results in a good amount of stop-and-go. Although once I had to go up to New Hampshire (from central CT) with my dad and my truck got about 300 miles to a tank since it was all highway, which still resulted in 16.6 mpg. Still not that good.

And get this, my driving habits prior to this resulted in about 200 miles per tank, which results in 11 mpg. Terrific. And it's not like I drive like a douche either.

So tell me, what can result in my truck chugging that much gas?! Is my gas gauge perhaps inaccurate? Although the truck does start stalling on stops after driving on empty for while so the gauge might be fine. And I also replaced my cap, rotor, and wires a few weeks ago. And I replace my air filter twice a year. Although I'm not sure how old the plugs are, I'll have to find out. Can old plugs really kill MPG that badly? What kind of mileage do you guys get?

 

1) I'm pretty sure you have a 20 Gal. tank. The funny numbers like 18 I'm pretty sure are for the second+ gens. You might want to check where you found that out to be sure.
2) You're not figuring your mileage correctly so you probably did get better than 14 mpg's. You have to divide the total number of miles by however many gallons you put into the tank. not just the number of total gallons the tank can hold. And i realize that may be hard if you're not always filling it up all the way, because then you can't always get a true MPG. Just to be sure, I would fill it up all the way, drive it and then fill up all the way again and do the math to get a definite number.
3) Where did you get a 15/20 rating for these old beasts?! Edmunds says 16/17 which yes is better than 13/14 but still, factor in age.
4) I got 12/14 all winter with mine. I FINALLY, for the first time started getting 15/16/17 when I drove everywhere in 4th gear as much as possible (you called it overdrive).

Other than that, you can do a basic tune-up. Cap, plugs, wires, oil change. You could spend the cash on a K&N air filter too but some people will disagree with that.

You could check to see if your engine is running rich or not getting up to temperature also. Mine was doing that for awhile which affected mpg's quite a bit. Running rich could be the FPR (fuel pressure regulator) and temp could be the thermostat (with those being the easiest cheapest solutions that you should be crossing your fingers for). I always get over 200 miles per tank. I don't fill up till around 250.

 

Thanks for the response but...
1) If so then my mileage is even worse (12.5 mpg).
2) I topped of the tank so maybe give or take half a gallon tops? My tank wasn't totally empty so I didn't wanna go by how much I put in. I'm not sure where the pumps cut off but I tried to squeeze in as much as I could.
3)All in the first sentence of my original post. 1994 S15 Jimmy 4-door 4x4 with the 4.3 Vortec CPI with 87 octane fuel.
4)EPA website:http://www.fueleconomy.gov/Feg/findacar.htm
But yeah I guess age can have a part.
I'll try topping it off again tomorrow and see what happens, but I remember averaging this range for a long time.

Almost all of the tune up parts (cap, rotor, wires, oil, air filter) are very fresh on my truck, except for plugs. But I'll have to check how old they are since I have no clue.

EDIT: I see that you edited your post....

 

I edited my post after I read over yours again. Sorry about that. I put in a few suggestions at the bottom

 

No problem... I make the same mistakes all the time lol. Thanks for the advice! Regarding the thermostat, my temp gauge (on the dash) usually hangs around in the 170-185 range. Is that OK?

 

I think you are figuring your milage wrong there.

Miles driven divided by gallons added. Im on litres and kilometers up here.

Set your trip to zero when you fill the tank (let it click off and dont top up). Then drive however much gas you want to, half a tank, full tank, whatever. Then fill it again and see how much gas you put in, and whats the trip say?

200 miles divided by 10 gallons or whatever numbers you get. Thats the most accurate measurement you will get.

 

Its also better to do it over a longer period (say a month of driving normally) to see what the MPG's are. It makes up for the "Mostly city/some highway" stuff. Its more of an average.

 

Thanks guys. I guess I'll run the truck to empty and then I'll fill it to the top and take note of how much I dump in. Although what about the fuel that's already in the tank? How much do you think is left if the gauge says empty and the truck stalls (from fuel starvation) on stops? Since I gotta have SOME fuel to make it to the gas station lol.

 

It makes no difference whether the tank is empty or half full at fill-up. Start at the next fill-up, zero the trip odometer or write down the mileage. Drive it one month and record the total number of gallons you buy. At the last fill-up divide the total miles driven by the total gallons bought. Simple as can be.

 

Its the simple things that I struggle with LOL. Thanks for dumbing it down for me hahaha. I'll be sure to do that.