OK, SO I wanted to see just "how bad" my gas mileage really was.

The one thing that works really well on my car is the odometer...

Last time I topped off the tank I recorded the mileage (248,927), then I drove it until it literally sputtered out... a little too far actually, because I had to use a gas can to put 1 half gallon in to get me to the gas station . This happened at 249,255 miles

I drove it to the gas station and topped it off again. I'm still having the problem of "Where is the rest of my gas" because I used almost all of the 1/2 gallon just to get there, but could only FORCE 18.7 gallons into the tank.

A little math with the calculator tells me that I avereaged a little over 18 miles to the gallon.

So, first question:

How does that compare to everyone elses mileage?

And...

Why does my car "run out of gas" when there is clearly AT LEAST 2 gallons of capacity left in the tank?

Feedback is much appreciated.

Rod.

 

As best as I can tell last time I checked, I was getting about 20 roughly. This was doing approx. Half my driving in town and half on the freeway. I didn't, however, run it completely out, but rather used gallons vs. mileage on the trip meter...

 

I tend to average about 22 mpg in the city and 28 when I am using the highway. But I did notice my gas mileage got better as I went to thinner air (where I had less torque and didn't feel like flooring it as much, since it was less fun (I guess haha) ). This was using Carl's Z's method below

but to be honest, I think the most I've ever gotten into my tank was 19.8 gallons and I was definately sputtering. I've heard on here that our tanks might have crap in them from 23+ years that is taking up space, or our tanks have been dented. *shrugs*

 

18 is bad. I'm probably getting 18 right now with my poorly running engine. I'm not sure why though.

I used to get 22/23 overall. Then with the 3.54 rear I was up to 24/25 average and 32mpg out on the highway to California. I was even running a little rich as my car would not quite pass emissions.

 

I am getting about 22-23 average. If you've got you foot in it all the time, it will drop below twenty...
Going to the Z meet in Portland Aug 13, be interesting to see my mileage for that trip with all the work I've done recently.

 

Wow, I guess mine is not doing to bad then. I am a little above 18 mpg all around town driving...a bit better If I am not flooring it all the time lol and that's with the 3 speed auto, no O2, exhaust leak, 3.54:1 gear, and tires that make it stay at 3,000 rpm at 55 mph. So I am sure once I put the 5 speed in here, fix the leak, and get the right size tires I should be around 40-50 mpg in the city....yeah right but it should be in the mid to upper 20's..I hope.

 

I used to get WAY better mileage than I am getting now. I am pretty sure my AFM is just toast. I'll swap it out and see what happens.

As for the tank capacity... My tank is not dented, so it must have A LOT of hard sediment at the bottom to take away 2+ gallons of capacity.

18 MPG overall with more than half of my miles on the freeway is pretty bad huh?

I figure that means I'm maybe only getting 14-15 MPG in town... LAME!

I need to find a good AFM now...

Rod.

 

Before the turbo swap my car was getting roughly 14-15 mpg HIGHWAY. I had the 3.9 coupled with an early 4 speed from an S30. On top of that most of my highway driving while I was calculating was up in the 75-80mph range (my trip cross country). The turbo I'm sure would've done much better but I never bothered to calculate it.

 

I'm sure that I lost some highway mileage when I put the '79 5 speed in the car because 5th gear is noticeably shorter, but... That alone won't explain my poor mileage overall.

Rod.

 

Or you're incredible dissapearing fuel Which magically reappears when you go to top off the tank

 

I think I am getting better mileage now, because I leaned out the AFM some. I am almost to 200 miles, and haven't burned a quarter tank yet. I will keep watching it though. I never thought moving the AFM a couple teeth clockwise would improve it that much. I know before the leaning out, I went 16 days one time before I had to fill up again. Which was between 20-21mpg.(And that includes quick take-offs, with mostly city driving) Of course my little fuel pump leaking problem dropped my miles. Because of the leaks, and I was pouring fuel on my back and arms. Fun times though.

As for filling the tank, when I get fuel. I put almost 18 gallons in my tank when I fill up. And the little red needle on the fuel gauge is still above zero. So I think my tank is fine, but I never tried to run it out. Because it can be a pain to get fuel again. And I calculate pretty much the same as Carl does. Except, my tripometer don't work. So sometime I would like to swap it out for another 130 speedo I have.

 

Ain't it the truth?!

 

Same with mine, hasn't been functional since I've owned the car. With your tripometer not working, how did you measure your mileage to calculate MPG?

 

Why not have the tank resto'd, Rod? Its cheap enough and then you can be sure you dont have a huge pile of crud at the bottom of the tank.

 

It is the old school way. First you write down what your odometer says, when you fill up.(I write it on my fuel slip) Then you drive your car like normal. When it's time to fill up again, write down the mileage it says. Subtract it from the previous mileage, and you get how many miless you did on certain gallons of fuel. Then you see how much it takes to fill it back up, and you then divide the gallons and miles. example( 369 miles, 17.76 gallons) Divide those 2 figures, and you get your MPG.

Here is a rough example on how you get the end result.

196,849 miles
196,480 miles
369 miles done on the tank
17.76 gallons of fuel
Subtract these 2 to get your miles. Then take the miles, and divide by the gallons.
369/17.76=20.7778, which would be rounded off 21 mpg.

And there you go, this should make it easier for you to do it next time. Hope this helps.

 

Math... It's a terrible waste...

 

I got 19mpg towing a "4x8" trailer weighing as much as the car from Virginia to florida.




It was a 1981 280zx turbo stock and the turbo crapped out halfway down so I pulled into a dennys, had lunch and cut up the metal shield of a floppy disc.

I undid the two bolts on the turbo drain tube and used the thin piece of stainless I had made from the floppy to block the oil drain so I wouldn't pump exhaust into the pan.

Then I disconnected the waste gate and replaced the T fitting with the oil pressure sensor.

Car still got 18mpg though I had problems with hills in that I had to go about 90 down them to still be at 55 at the top of the next one.

It was auto 3 speed with 3.54

Of course, I had disconnected the 02 sensor before the trip and played with the spring to net a relatively lean mixture during steady state cruising.

It was hairy in traffic but not as hairy as when I towed a maxima on a car dolley with the same car.

 

Ok I am getting 22 mpg with my bad afm. You just have to know when to adjust it. the only thing I could think of your low fuel capacity, is crud in the tank. you can pull the carpet up and do a check through the floor into the tank. I did mine, and it is clean enough to eat out of. my 79 2+2's tank was another story.
If you know your afm is toast why not do what I did and experiment by puting a little tention in the spring a little at a time, and see what happens.

 

oh yea my speedometer dos not work, but I normaly run 3500rpm down the road. so take that for good gas milage.

 

Ah, I thought it would be obvious that my odometer didn't work too when I said the tripometer didn't... I guess they don't die at the same time though. Anyway, both of mine seem to be non-functional, trip and odo

 

does your speedo still work?

 

No it's cool, I thought yours would be the same as mine. If I reset my tripometer, it will go to 9 miles, and stop. I never could figure out why that was. And I am just too lazy to swap out another speedo. But yeah like J asked, does your speedometer work at all? If not, that would explain why nothing is working. Because most cases if the odometer doesn't work, your speedometer, wont work either. And that usually is a speedo cable issue, I would check it out. And make sure it is hooked to the tranny, and the back of the cluster. If it is, you either have a bad cable, or the speedo is bad. I swapped out my cable from my '81. After I found out the '82's was no good.

 

Yup, it sure does. I don't think it even wobbles any. And its dead on with the radar speed displays around town.

 

To start off with mine is a 1979 2+2 with full interior, powersteering and disconnected (no belt) air conditioning that is obviously never used. While most everything on my car works perfectly (electrically speaking) other than my temp and fuel gauge my fuel light does still work so I know to fill up whenever the light comes on. I get about 300 miles to the 18 gallon tank so that figures Im getting roughly 16.6 mpg but, Im not driving it bone dry. All of my driving is done in the city and I shift at 3k except for a couple times during the week when I get on it in first and second. Does anyone have any idea how much fuel is left from when the light first comes on until the car dies? either a mileage estimate or fuel volume would be fine for me.

Oh and my EGR is completely disconnected so, Im sure that has a great deal to do with the mileage, my tires are slightly underinflated, and I think my timing is still too advanced as well as my cam gear being set at the #3 position (not sure if that makes a big difference)

 

Oh and I messed with the IAC to get the idle where it should be, I guess that could've also affected the fuel mixture for the worse.