Low gas milage - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 11 (permalink) Old 02-12-2011, 08:03 PM Thread Starter
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Low gas milage

What could be the reason why my Z all of a sudden gets 12mpg when for the last 2 years has been consistently at 17mpg?

Spark plugs are not fouled, cap and rotor don't look nothing out the ordinary, the fuel filter is due to be changed soon but its not past schedule, the injectors are barely 2 years old, same with the wires . I don't drive any harder than I usually do. What happened?
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post #2 of 11 (permalink) Old 02-12-2011, 09:31 PM
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Re: Low gas milage

decay. Check out the hoses, air filter, fluids, connections, tire pressure.


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post #3 of 11 (permalink) Old 02-12-2011, 09:41 PM Thread Starter
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Re: Low gas milage

My coolant and heater hoses are all fairly new. Air filter is also fairly new.

As far as fluids are concerned, coolant was drained and refilled about 4 months ago. Also had my front pads replaced along with a clean and adjust on the rears the same time. The brake fluid was flushed about a month later.
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post #4 of 11 (permalink) Old 02-12-2011, 09:46 PM Thread Starter
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Re: Low gas milage

And when I say all of a sudden, it was seriously ALL OF A SUDDEN. One fill up it was 17mpg then the next one it was around 12. And it's been 12 mpg the last 2 rounds. I don't get it.

The engine is bone stock.

Its a 77 280z 5 speed BTW.
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post #5 of 11 (permalink) Old 02-12-2011, 11:23 PM
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Re: Low gas milage

not that familiar with the s30 but if the coolant sensor went south (analogous to the chts on an s130) then the ecu would be giving the engine extra fuel thinking it was dead cold. does the s30 have the cold start valve? does the exhaust smell of unburnt fuel? fpr went bad and your fuel pressure is way higher than it should be. some things to think about

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post #6 of 11 (permalink) Old 02-13-2011, 12:57 AM
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Re: Low gas milage

Yeeeep, mine went from 23 to 16. Sucks. I've tried a lot. Changed out the fuel injectors...it does run better, but the reports were that it got 20 mpg. Then dropped to 16. So I went up there today and found the hose to the CSV had backed off 3/4 " and the clamp is nowhere to be found. Why did he not smell gas????

Chattanooga, TN 82 white w/ red na coupe 153,000 83 2+2 330k mi 82 Black/buck 126k mi
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post #7 of 11 (permalink) Old 02-13-2011, 07:29 AM
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Re: Low gas milage

yes you could unplug the cold start injector as an experiment, and test the wires at operating temp. If the car is warm and you got a signal going to the CSV then its dumping gas, because a temp sensor is stuck on cold


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post #8 of 11 (permalink) Old 02-13-2011, 07:55 PM
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Re: Low gas milage

Quote:
Originally Posted by palladin
Yeeeep, mine went from 23 to 16. Sucks. I've tried a lot. Changed out the fuel injectors...it does run better, but the reports were that it got 20 mpg. Then dropped to 16. So I went up there today and found the hose to the CSV had backed off 3/4 " and the clamp is nowhere to be found. Why did he not smell gas????
I bought an '83 several years ago that got pretty poor mileage when I got it (around 18 - 20). Changed out the O2 sensor and it jumped up to the normal (in my experience) 25+. This won't matter on a '77 but it might help you, Palladin.

'76 280Z 2+2 4sp, silver, stock drive train, MSA air dam and rear skirt, black interior, 120K.
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post #9 of 11 (permalink) Old 02-13-2011, 10:33 PM
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Re: Low gas milage

I changed it out already. The emission tech does not like Bosch though, says Denso is better.

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post #10 of 11 (permalink) Old 02-14-2011, 09:26 AM
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Re: Low gas milage

check your vacuum advance canister.

if the diaphragm breaks then you can lose a good amount of mpg.
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