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So I heard these cars are rated to 27mpg highway?


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So after searching around I couldn't find anything on this site related to gas mileage. So I went to google and found that the 280z is rated about 18mpg city and 27mpg highway!

 

Well I'm running a mostly stock 280z (just intake and 2.5" straight exhaust) and I'll get 16-18mpg cruising 50% highway at 70mph @ ~3800RPMS, and most of the rest on country roads at 55mph @ 2500RPMS. I think the only other things affecting mileage would be wider sticky summer tires (225s) and a 3.7 rear diff, but would that really kill my mileage that much? I have new plugs and wires as well, and my car idles rock solid at 750rpms, but I don't have a wideband (yet) to check my AFRs

 

Are other people getting similar mileage, or is my car running too rich for some reason?

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I used to get 27-29 highway mpg, driving in Colorado about 70-75mph.  I was running a stock turbo engine with the Z31 ECU, 205/60/15 tires, and no aero mods except an air dam.

 

T5 transmission, 3.54 rear gears.

Edited by SleeperZ
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I've got the stock 5-speed 280Z Trans and an air dam too. I figured the 3.7 rear end would hurt mileage some, but this seems extreme to me.

 

Its odd that some people get over 25mpg and others are stuck below 20. What gives?

 

I know I had a bad coolant temp sensor on a previous car that was causing a rich condition, so I replaced the one on the Z, but apparently there are 2 on this car? I replaced the small, single wire one. It's not really a huge deal since next year I will be going turbo and converting to a MS ECU, but if there is something simple and cheap I can try in the mean time I'd definitely do it. Premium is expensive!

Edited by osirus9
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I got around 35 MPG on a trip this summer in mine.

 

'73, with a 2.8L and turbo (N/A 2.8L + turbo), running Delco (GM) EFI, 5 speed trans, 3.9 rear, 225/50/16 all around, My girlfriend, myself two dogs (smaller dogs) and some luggage. I was light on the throttle and almost no stops for over 4 hours so a pretty consistent 70 or so MPH.

 

Most of the time I get WAY less than that, but it's how I drive it. I beat on my car like it's stolen, which means the throttle spends more than enough time at WIDE OPEN, which makes my fuel consumption go way up. If I drive it sanely, fuel mileage is great easy to 20+ MPG.

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huh, well I know my timing is fine, I already checked that. I'm using some unknown injectors though. You'd think they would flow less over time instead of more though?

 

Any options to check them without having to send them away?

 

They will flow unevenly, so the fuel will not atomize as well, and the result is more fuel is needed for the same power level.

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On a recent trip to the Datsun show in Williams AZ, I logged 1000 miles. The first half I was going about 85-90 mph (got busy at work and couldn't leave early) and got 24 mpg. The second half I was able to cruise back home with the other club guys. The 1200 we were with had 12" wheels so we went the whole way at 65mph, that netted 33 mpg. This is on a high comp l28 with mikuni 40s, verified with GPS and an ohmmeter.

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In my old 280ZXT with 3-speed auto I was getting 22 at best. This was completely stock. I never actually measured mpg with the Z31 ECCS/MAF setup. So I imagine by just adding a 5-speed you could be sitting at lower RPM on the highway and easily push that number upwards.

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Many Nissan ecus whether 280zx turbo, z31, and others will switch to open loop and ignore the 02 sensor usually within 100rpm of 3500rpms.

 

These cars were made when there was a 55mph speed limit and were never expected to cruise at speeds that put the rpms above that point.

 

Two solutions are tuning with nistune if you are using a Nissan ecu or gearing it such that you aren't over the rpm in which your ecu goes into open loop at your desired cruising speeds.

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How can you run in closed loop without an 02 sensor? There was no 02 sensor on the 78 correct?

 

And I'm sure my mileage will improve later with an aftermarket ecu, but in the mean time I was still curious about other people's experiences. It seems like half the folks here get over 25mpg pretty easily, while others can't get 20mpg to save their lives. It just seems like a pretty big gap to me is all.

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'77 280Z, NA with '83ZX 5-spd and 3.90 R200.  Never got better than 24 MPG.  I log every fill-up at the service station - #gallons, cost, #miles driven, and actual calculated MPG. I've done this for over 40 years with all my cars starting with my 1970 'Cuda.

The interesting thing is that the same 280Z, 200 lbs heavier but now running an LS1/T56/3,70 R200 LSD, gets the same maximum 24 MPG.  Guess it's pretty much about aerodynamics.

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How can you run in closed loop without an 02 sensor? There was no 02 sensor on the 78 correct?

 

And I'm sure my mileage will improve later with an aftermarket ecu, but in the mean time I was still curious about other people's experiences. It seems like half the folks here get over 25mpg pretty easily, while others can't get 20mpg to save their lives. It just seems like a pretty big gap to me is all.

 

The 280z has no closed loop operation but it is possible that it also goes into a pretty rich map at the 3500rpm mark.

 

I haven't hooked one up to an ecu simulator in about 3 years so I don't really remember if it goes full rich at 3500 like later ecus or simply follows the airflow meter and uses a map without changing modes.

Edited by HowlerMonkey
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