# D21 gas milage issue



## Jpmc (Sep 19, 2019)

I have a 1994 Nissan pickup D21 two wheel XE, which I purchased new. Over the past few months the milage has dropped from 21 MPG to 14 MPG. The engine has 302,000 miles on it and has been trouble free up until now.
It runs fine, but the milage has dropped substantially. I just had the oil changed and ask the mechanic to check the milage issue. He just said it's old. Not the answer I'm looking for.
Any help will be appreciated.
John


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## rogoman (Dec 16, 2004)

The bad gas mileage could be caused by the following:

- Low compression.
- Worn spark plugs.
- Leaking fuel injectors.
- plugged up air filter.
- major vacuum leak in the intake system.


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## Jpmc (Sep 19, 2019)

rogoman said:


> The bad gas mileage could be caused by the following:
> 
> - Low compression.
> - Worn spark plugs.
> ...


Thanks, I'll check them out one at a time.


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## smj999smj (Jan 1, 2006)

Excessive fuel pressure can cause it, as well. So can a bad oxygen sensor.


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## 2016 Versa (Sep 24, 2019)

Could be a bad 02 sensor. When they go bad it's not uncommon to see a 25-40% decrease in fuel mileage. I used to drive an '88 Ford Escort that as a normal rule got 40-43MPG. When the 02 sensor went bad the mileage dropped to around 30MPG. If you find out it's the 02 sensor you can usually buy them cheaper on eBay than at a local parts store. I've bought 02 sensors on eBay for about $10 that would have cost me $60-70 locally.


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## zanegrey (Dec 5, 2005)

check tires and wheels
make sure no brake dragging.
check heat range of engine...
302 k miles when has the t-chain been replaced..are you hearing engine Moises ..?
is the idle changing..?


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## zanegrey (Dec 5, 2005)

it being such a simple thing...


read the codes...


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## mrholmnquist (Oct 16, 2019)

Also possibly a catalytic converter which is beginning to get blocked will affect fuel economy and also reduce engine power


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