# Poor Gas Mileage on 94 1.6



## itp (May 2, 2006)

I have a 94 Sentra LE with 168,000 miles. When I first got the car last year, it was getting 26 mpg city, and 35-40 highway. Now, it's getting 20-23 city and less than 30 on the highway. The car runs good, aside from the poor mileage. I keep the tires at 32 front and 30 rear. 

So far, I have:

cleaned TB, IACV
replaced fuel filter (purolator)
used fuel injector cleaner for 2 tanks
seafoamed through intake and several vacuum hoses; also crankcase
switched to full-synthetic oil (royal purple), instead of dino
relpaced air filter with k&n
replaced spark plugs (it had bosch in it, from previous owner) with ngk, from the dealer
replaced plug wires, distributer cap and rotor (oem from the dealer)
replaced pcv valve (oem from dealer)
fulshed and relpaced coolant (added water wetter.. don't notice a difference on the dash thermo)

Before all that, I was getting 20mpg city, now I get 22-24. Tonight, I replaced the hose for the pcv valve (didn't look like it was getting good airflow). 

What should I do next? Tomorrow, I plan to check the MAF sensor, and anything else that isn't too time-consuming. My next day off, i'm checking for ECU codes. What else should I look for, though?

Also, how badly does the a/c affect gas mileage on these cars? I'm running at higher fan speeds than last summer, and running the a/c more often and longer in general. Could that possibly add up to 2-3 mpg city and 5 or more highway?


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## Tinus (Feb 1, 2005)

Hi ITP,

Checkin' your mileage is best done on a route you drive often, like from home to work and back for instance during a week or 2-3. Start with a tank full of gas and your counter reset to zero. When you tank is empty, or the warning light goes on, note the mileage you have, fill up the tank, reset the counter and drive it again till it's empty. Etc etc. You know how much gas your tank holds, so with these figures you can get an average mileage during a longer period of time in all sorts of conditions.

A lot depends on how you drive; push the pedal 2 the metal and it's byebye gas. Keep your foot featherlight and drive relaxed, you will have much more miles on the same amount of gas. If you have a manual gearbox, you can save A LOT by shifting up fast and keeping your rev's below 3500 RPM (yes that can be done .

I drove like 400 km on 40 litres of gas (full tank - NX1600 with a GA16DS (elec. carb) manual gearbox). As 4 today I must pay a pure insane EUR 1.40 per liter gas (EUR 1 = $1,20)!!!!!!! I had to adapt my driving before going bankrupt... I now shift up very fast drive low rev's all the time and i manage to get an fantastic 600 km out of 40 litres of gas )

I think your airco can affect mileage indeed. As its compressor drains power (not to much) from the crank, it uses fuel one way or another, and electricity. That has to come from somewhere... You can test it as argo above by driving a while with, and then without the airco on.

Good luck!


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## HATEnFATE (Dec 24, 2002)

on a 1.6 litre, your AC is going to kill your Fuel econ. it hurts my 2.0 pretty bad. 
Everything your done is a good thing in the right direction but I think your reading into it a little to much. How long have you been getting this mileage and what types of temps do you get it in?

In the winter your car will take longer to warm up and we tend to let them sit idle longer. That eats fuel economy. 

In the summer we tend to run the A/C and drive a little faster. That also burns fuel econ. 

If you want real good fuel economy, you need to see how easy you can drive. Like was stated before, the faster you accelerate, the more you run your a/c, the harder you are on the car, the lower your gas mileage will be. 

Try to baby the car for 2 full tanks of gas and see where you end up. Shift at lower RPM's and keep your foot a little higher off the floorboard. You'd be surprised how much you can save. 

In town I average 22-24mpg in my 91 SE-R. I lead foot around too. 
on the interstate averaging 75-80 I can get up to 35 mpg depending if I have to speed up or slow down alot. 

try a few different things and see where you end up and then let us know. so far what you've done sounds good.


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## RBI*04 (Sep 10, 2004)

the easiest way to calculate gas mileage: fill the tank COMPLETELY topped off, untill you cant get ANYMORE gas in there. reset the tripometer. drive until you need gas again (doesnt have to be with the gas light on, or running on fumes) and fill the tank again, till you cant fit anymore gas in there. now take your miles youve driven (look at the tripometer) and look at the gas pump, and divide the miles by the amount of gas. and there you have it!! very precise gas mileage.


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## HATEnFATE (Dec 24, 2002)

I don't want to be rude but where in this thread did it say anything about problems calculating fuel economy?

ALSO...overfilling your Fuel system like that is the WORST POSSIBLE THING you can do. Your going to get gasoline backed up into your charcoal canster and damage it. They aren't cheap and you only get like 1/2 gallon extra at most. Fill it till it clicks. If you know there isn't enough gas in there or you question it, squeeze again and if it clicks within a few seconds, stop.....YOUR FULL...IT CLICKS FOR A REASON!

P.S. unless your CEL is on, you wont have any Codes in the ECU. Your still running OBD1


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## RBI*04 (Sep 10, 2004)

HATEnFATE said:


> I don't want to be rude but where in this thread did it say anything about problems calculating fuel economy?
> 
> ALSO...overfilling your Fuel system like that is the WORST POSSIBLE THING you can do. Your going to get gasoline backed up into your charcoal canster and damage it. They aren't cheap and you only get like 1/2 gallon extra at most. Fill it till it clicks. If you know there isn't enough gas in there or you question it, squeeze again and if it clicks within a few seconds, stop.....YOUR FULL...IT CLICKS FOR A REASON!
> 
> P.S. unless your CEL is on, you wont have any Codes in the ECU. Your still running OBD1


i fill my tank like that EVERY time, and have never had a problem :dunno:


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## HATEnFATE (Dec 24, 2002)

At my dealership we replace 6-8 canisters/month because of people who overfill thier tanks.


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## travis_k (Jan 14, 2005)

One item you haven't changed that can cause poor mileage is the O2 sensor. If it has not been changed in 168K its probably overdue.


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## Twiz (Aug 24, 2004)

I agree, you should test your O2 sensor, it's prolly one of those heated ones they're supposed to last 80K-100K miles. Since it's an expensive part you should run some tests on it before looking for a replacement, you'll need a digital voltmeter for this. I noticed a great improvement in gas mileage when I replaced the stock BOSCH one with a NGK heated sensor (think it was $54 shipped about 2 years ago). I replaced it at 96K miles after some tests.


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## itp (May 2, 2006)

HATEnFATE said:


> How long have you been getting this mileage and what types of temps do you get it in?


It's been since before it started getting hot here. I live in Florida, so it's mostly hot, humid weather. 



HATEnFATE said:


> If you want real good fuel economy, you need to see how easy you can drive. Like was stated before, the faster you accelerate, the more you run your a/c, the harder you are on the car, the lower your gas mileage will be.


That's the thing. The way I normally drive, I was getting 20 mpg. I've been going easy on it lately, and that makes a little bit of difference. The car still isn't getting the 26 mpg it was getting when I got it, and that was only 8 months and 10k miles ago..



HATEnFATE said:


> Try to baby the car for 2 full tanks of gas and see where you end up. Shift at lower RPM's and keep your foot a little higher off the floorboard. You'd be surprised how much you can save.


It's an automatic with no tach, so I have to leave shifting to the computer. 



travis_k said:


> One item you haven't changed that can cause poor mileage is the O2 sensor. If it has not been changed in 168K its probably overdue.


That was next on my list, but unfortunately it will have to wait until next payday.


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