Nissan Sentra 2001: to much fuel is required

timeau

Hello everybody,
Does anybody know how to solve the problem:
My Nissan Sentra GXE, 2001, required too much fuel, so I have to fill a tank each 210-220 miles (i.e 20-21 mpg instead of 26-27 at city and 22-23 mpg instead of 32-33 on highway). I was asking dealership to fix this problem 3 times:
1. I got an answer that all has been fixed (quite true, became 23-24 mpg at city). But two months ago all came back, 20-21 mpg
2. They said that nothing wrong with my car (Do you believe?! I don't...)
3. They asked the detailed 2 months log how much fuel have I filled and how many miles I drove.

Do you know how to solve this problem?
Thanks.

carlmoorejr

My 94 SENTRA with the 1.6 engine and 105,000 miles is averaging 28 city/hwy combo. 33-35 on trips. You did not say how many miles you had on it, but if it is around 30k you might need the injectors cleaned[not cheap at dealer].It probably would be about time for new spark plugs and maybe a new fuel filter{also not cheap}. Maybe check your air filter and keep an eye on your air pressure in your tires. You might want to change brands of gasoline and go with a name brand such as CITGO etc. Limit your idle time and just coast to a stop and start off easy. I am not a mechanic so these are just suggestions. You may have already tried some of the above. I would think you should be getting quite a bit better than you are. The log is a good idea, just make sure you put the same amount of fuel in each time.IE:top it off or stop it when it clicks off. GOOD LUCK.

timeau

My car has just 22.000 miles. Air pressure is always OK, I check each week. I tried to use gas from any brands (last time I use Shell), but the same result. How do you think, will be it possible to change/check some of parts you have mentioned by Nissan warranty? I am able to change air or fuel filters myself, it is not a big deal, but to fix injectors... :-(
Anyway, thank you for your responce. Will "kick" dealers again :-)

carlmoorejr

I doubt at that mileage if your injectors are clogged up. But it is possibly if you have been getting fuel with contanimants in it. The dealer probably would claim this falls out side your warranty work. {as routine maintenance}. I do not know, I guess it would depend on your relationship with the dealership. I was under the impression the fuel filter was difficult to change,so I have always left it up to dealer.{I could be wrong}. Spark plugs are probably o.k. ,& easy to check. I have incountered some strange problems in all the years I have been driving. One other "remote" possibility is your odometer,tripometer,speedometer could be inaccurate causeing it to show less miles on it than it is actually going.{not very likely this is the problem}You could check that out against a friends car. Maybe go to another dealer if that is possible.They might have a suggestion someone else overlooked

tboner1965

Does your car have a temp gauge? If so, is it low, high, normal?

It is possible that a stuck open thermostat would cause the engine to run cool. Cool engine uses more fuel. I would suspect the Check Engine Light (CEL) to come on.

Do you have a stuck brake somewhere. Does the car pull to one side? How about coast down? If you put the car in neutral and let it coast, does it seem to coast ok, or do you feel drag.

Is this an automatic or stick shift? If a stick, how long are you holding each gear? Are you running to redline before you shift, or the other extreme, do you "short shift" at low RPMs?

If a manual, does the clutch slip?

If an automatic, is the overdrive (O/D) turned on (many cars have the ability to turn off the O/D) and that would certainly cause problems. Also, if your car has a locking torque converter, if it doesn't lock up it could cause poor fuel economy with giving any driveability issues.

And of course, I have to ask the obvious question, are you calculating MPG based on the tank capacity or how many gallons you put in the vehicle?

timeau

"Does your car have a temp gauge? If so, is it low, high, normal?"
Normal in any case. I have never had problems with temp.

"I would suspect the Check Engine Light (CEL) to come on."
I hope it will not. No, not yet.

"Does the car pull to one side?"
Yes, a little bit. But I have heard that in US it should be so for better water draining... I mean that roads have "^" profile.

"How about coast down?"
I didn't pay attention, but I didn't see anything wrong... Of course I can be mistaken...

"If an automatic"
Yes, it is.

"is the overdrive (O/D) turned on?"
No, but I have such an opportunity. I used it a few number of times for last year.

"Also, if your car has a locking torque converter, if it doesn't lock up it could cause poor fuel economy with giving any driveability issues"

I think I do not have it. Sentra is rather cheap car...

"Are you running to redline before you shift?"
No, moreover, it is difficult. This engine has a max torque at 2400 RPM, so transmission try to make engine use these RPMs...

"or the other extreme, do you "short shift" at low RPMs?"
I think, no. I didn't change my driving style, and I have never had such problems on other cars.

"I have to ask the obvious question, are you calculating MPG based on the tank capacity or how many gallons you put in the vehicle?"
It will be easier to describe my calculation scheme :-). I fill my tank "by edges" and reset the odometer (sorry, if I mix up with names). When I need to fill the tank again, I can see, how many gallons (N) should I fill at THIS, not THAT time and how many miles (M) had I driven. I just divide M to N and result is ready - about
22-23 mpg on highway and 20-21 mpg in city.

BTW: Today I was in another (third) dealership again. I got an answer that they saw 27-28 mpg on highway (even if this is true, it should be 33) and I am not to complain.

tboner1965

If the car is an Automatic, then it is shifting on it's own.

I would be suprised if it did not have a locking torque converter, as most cars today do, even the cheap ones. Especially since cheap cars are often sold on their economy merits.

I am curious how the dealership is measuring fuel economy, since I doubt they are driving a significant distance.

Unless....

They measure fuel economy the same way the Federal government does. When the EPA measures fuel economy, they don't measure how much fuel is used. Instead, they run the car on a dyno and measure the components of the exhaust gas, plug this into a formula along with other values such as the weight, frontal area, drag coefficient, and perhaps the phase of the moon (just kidding about the phase of the moon thing) and then the derive the fuel economy.

However, this really isn't real world, as there are many other factors that impact fuel economy, such as low tire pressure, head or cross winds, how much you carry in the car (a small car is much more suspect to any extra weight you carry in the car), that Yakima bike rack you might have on top really provides a lot more drag.

Even my 1987 Buick LeSabre, at over 3600# has wildly varying fuel economy. I have seen from 19 MPG to 31 MPG over the course of the past 14 months. But the long term average is right at 23 MPG.

I suggest filling up, letting the pump stop at the very first stop and then keeping a log for 4 weeks. Record you mileage at the beginning of the period. Indicate the types of trips and distance, such as stop and go, interstate/freeway, or other significant characteristics, what kind of traffic, weather and what not. And of course, record every time you add fuel and the amount.

At the end of the four weeks, fill up at the very same pump, and again stop the pump on the first automatic shutoff.

Then add up the number of gallons and the total number of miles travelled.

I suspect this will be more accurate as you will have a much larger sample.

Then look at your MPG and compare that with the type of driving you do.

In my case, four weeks is about 2500 miles, so I get a pretty good sample. I find I use about 105-110 gallons of fuel per month.

TB