mpg?

[z_boi]

me again, I was wondering how many miles per gallon on a 78 280z(stock) should i expect, I'm not quite sure about how mpg i am getting but it seems as if im gettin very little mpg? any one know?

If there anything i can do to improve my fuel economy?

Thanks again!

[GunnerRob]

Hi z_boi

I had a '78 and now have a '75. They both got around 20 mpg on the freeway and 17 mpg around town. Both of them had 4 speed transmissions and were pretty well maintained.

I now have an '81 5 speed in my '75 and am getting about 25 mpg on the freeway. The 'around town' mileage is about what is was with the 4 speed.

[Smokey]

You should be able to go about 300 miles between fillups. That is pushing it. I usually filled up at 250 miles. That was around 20 miles/gallon, and was a '72 240Z.

[Biz280Z]

I used to have a 72 I drove as my daily car. I always got about 25 to 26 mpg unless I let the oil get low in the carbs. If that happened the mpg dropped. In fact on one long trip I got 30 mpg. Currenly I have a 78 and when I checked the mpg I was getting about 25. If you get less I would believe you have lead in your shoes or it's not tuned right.

[Inf]

I've been waiting on my service manual for about 6 weeks, Andy from datsundude.com has been waiting for a shipment since then. My Z has been getting absolutely horrible gas mileage since I got it. I haven't really driven it much because I haven't had time to make it inspection legal until now(spring break now!).

I filled it up about 90 miles back and it is already near the E on the gas guage. Since I have no documentation yet, maybe you guys could give me some info so I can do some investigation

1) How many gallons will go into a 72 240z tank before the pump shuts off (total amount the tank will hold without topping off or anything)?

2) What could be the possible causes? The exhaust smells like it is running a little rich, maybe the carbs aren't tuned right? Need more oil in the carbs? How do I tell if the oil is getting low in them? Idles around 700-800 RPM, but it doesn't feel as smooth at idle as some of the other vehicles I have driven. Before, I figured this was simply a characteristic of the vehicle.

I haven't really been driving it wild or anything yet. Just the occasional acceleration from a stop light to get a good feel for it. Even if I had been driving it with a lead foot, I doubt it would cause under 10 miles per gallon! With gas prices at such extreme levels, I am very reluctant to drive it at all until I get this working right.

I am pretty anxious to get my service manual so I can really get to work on things.

Thanks for any info you guys can give me,

Andrew

[beandip]

It sounds to me that you need to ballance the carbs and adjust the mixture. As for the oil in the carbs , there is a line on the dampiner rod that shows the oil level . If you over fill the oil in the carb it will just go into the carb throat and into the fuel mixture and be burned with the fuel, no worries they only hold about 1 tsp full. My '73 tank holds 15 gals it says it on the gage if you look closely in red. When the carbs are in tune and the timing and plugs are all set as well as the valves the engine should be s m o o t h .

[Mudge]

I was getting 15 MPG when I first got my 240Z, if your getting 90 miles on a 13 gallon tank that is 6.9MPG! If the gas isn't litterally leaking out, something is very, very, very out of tune!

How do the plugs look? I felt horrible getting 15 MPG, I can hardly imagine anything worse on these tiny little engines. I am around 20-22 now, with dual DGVs and I believe a 3.90 R200 (only guessing because that is what my RPM agrees to). I do 3400-3800 on the freeway with my early 5 speed (.864 OD), but do mostly commuter driving to San Fran, which is semi stop and go.

[z_boi]

i have a stock 78 280z fuel injected.

[Mudge]

Lots of possibilities, bad AFM etc, a fuel injected car should turn 25+ MPG.

[sjcurtis]

In my 240Z I installed an injected L28 in Australian trim with the standard style injection, management trimmed to my own settings and it regularly returns 26+ MPG in town and 30+ MPG on Highway cycle. To this I run a 3.9 diff ratio through the a 5 speed box.

my 2c

Steve:classic:

[dozer171]

i would regularly get 24 mpg on the highway with my 78 280Z, but that was also with getting easily bored in fifth gear, dropping her down into 4th, sometimes 3rd taking off, putting her back into fifth and slowing back down... i would say you should be getting around 26 mpg or so if you have a five speed.

[z_boi]

does anyone know how big the gas tank is? It seems to me as if it is about somwhere around 15 gallons. not sure. but my gas mialage seems pretty bad rite now. i tinks i pumped about 9.5 gallons in when i still had about an 8th of a tank left. i got about 7/8th of the tanks filled. but im now below a half a tank and have only driven about 60 miles. i guess you can say its somewhere around 10miles per gallon. thats not very good. well. next i fill up on a full tank. i'll make sure i reset the trip meter. And i'll let you guys know.

[Mudge]

13 or 13.5 gallons. Do not let it run down and leave you stranded before you calculate MPG. Go fill up the car (dont top it off, just let the pump shot off normally). Drive it around until you get to the 1/2 tank marker if not 1/3 or so, and then fill it again.

However much you put in (7 gallons or whatever), versus how many miles you went is how you calculate. 7 gallons and 140 miles would be 20MPG.

I have noticed that on my 73, the gas gauge does not read linearly, many cars are like this. You will have to get used to what the gauge means, but generally once you calculate your average MPG you should know by # of miles how much gas is gone and how much you have left about. When I hit the 1/2 way point on my gauge, it starts going down fast, so it is obviously not reading linearly.

[Victor Laury]

No matter how you do it, you need lots of data. I have a log book and enter into it religiously. MPG varies from 23 ~ 10. Average 15 MPG - But I have a very heavy foot.

[2ManyZs]

Fuel tank capacity for a 240 is 15.9 gallons.

280's had a slightly larger tank at 16.3 gallons if I remember right.

Have you checked your vent hoses on the tank to see if any are blocked off or crimped? You may have trapped air in the tank while filling it, and therefore not getting the tank full.

[z_boi]

ok, i jus filled up today, put in about 12 gallons, according to my guage, it is almost full. which means i have somewhere around a 13-14 gallon tank, which according to 2ManyZs is incorrect and that i have a 16.3 gallon tank, i dunnoe, n e way. i will keep track or my miles per fillup and report bak.

[Mudge]

I sure thought it was a 13-13.5 but I guess I am incorrect(?)

Just keep in mind gas gauges are almost never accurate, usually this is because of the float device and the shape of the gas tank, modern cars are often the same way depending. My 94 Camaro for instance, same thing, 1/2 tank on the gauge is really 1/3 tank. I have to burn 5 gallons after filling it (not topping it off, just full) for it to say 4/4 FULL.

For my 73 240Z it is probably similar, when it gets down to 1/2 tank the tank empties FAST thereafter. So I assume it is around 1/3 or so. Either way, to get an accurate number you should fill it, so that you can fill it the second time around, but you should be pretty close so long as you dont get sloppy with the math, break out a calculator if needed

[z_boi]

Ok. Now im pretty sure that im getting around 10 miles a gallon or so.

So what is there i can do to fix it. Again, I have a 78 280z fule injected. Seems like i have a vacuum leack, can that b a problem. but i cant seem to find the leak.

My timing might b off, seems like i have no more room to turn the distributor to get the timming right. it say timing mark 10 under the hood"s lable. Help me out guys.!

[tanny]

I'm getting great mileage with my 73 240. The trick is to put in a 3.9 rear end and not change the speedo gear. I seem to be getting around 30 mpg. Not bad for a six with triple Webers. Dream on.

[z_boi]

I have a 78 FI 280z with the stock r200 3.545 rear, with the stock 4 speed. Only thing i'v done is put on an k&n cone filter.

Im getting about 10 miles per gallon. What could be the cause?

My injectors dont seem to b leaking. but like i said earlier, i have a vacuum leak, but i cant seem to find it, so not sure if it is a vacuum leak. And my timing might be about 4-5 degree advance.

the timing mark under the hood shows 10 its at about 4 or 5 but i have no more room to turn the distributor to get to 10i can only turn it the other way.

[z_boi]

ANY ONE?