Any mechanics on board? Bad gas milage

[I.rar]

My 2005 altima 2.5 has been getting around 15 mpg (rated at 21/29 city/highway) with just over 70k miles on it. It runs fantastic for a 4 banger and hasn't given my any trouble. No check engine lights or anything funny, just bad milage. I run full synthetic oil and regularly change along with the spark plugs and air filter. 

Aside from replacing the o2 sensors, what else could I look into? 

[A-Jay]

Tires pressure &  wheel alignment OK ?

A-Jay

[00 mod]

Also a fuel injection cleaning could be needed.

Jeff

[Buckeye Ron]

Vacuum leak in the intake system? CAT plugged up? Also check the front O2 sensor. The rear sensor basically just monitors the catalytic converter system.

Unfortunately, the Nissan 2.5L has a history of less than great mileage. Hope you get it figured out. 

[I.rar]

Tires are pretty new and were recently rotated. 

I've been told those injector cleaner additive stuff isn't that great for your car. Any truth to that? Or am I better off taking it to a shop. I can do basic stuff like brakes, plugs, oil and sensor changes but never done anything more. 

Can I test for vacuum leaks myself? 

Thanks guys, I appreciate it! 

[tipptruck1]

I am not a mechanic, but I do know my way around cars. This could be caused by a bunch of things. Lets start with the basic stuff. First check the air filter. As most need to be changed every 50-70k. Next check the spark plugs, cables and distributor. The plugs you can check you self. The distributor will have to be checked at a shop. Also see if you can change the fuel filter. While we are on the subject of gas. Buy your gas at a few different stations. I have had bad gas in my car. And thanks to me going to a different station. It saved me a lot of money.

Now for the not so easy stuff. There could be a sensor, camshaft, valves, injector, or other things. That could be causing this to happen.  My best advise if let them hook it up to a computer. They will be able to tell if its your injectors, bad fuel to air, timing, etc. Around here its about 60-100 bucks for places to test it. In my eyes it is worth it. Better then buying stuff and finding out you didn't need it, or its still doing it.

[I.rar]

I do have a good/trustworthy mechanic I've been going to for years that I could have check out but was hoping for maybe a quick fix or simple diagnostic. 

Thanks! 

[Jtrout]

What grade of gas do u put in? Do u drive like a bat out of hell? Lol i would check the basics that have been said and change the fuel filter

[I.rar]

Regular unleaded. 

I drive like a normal person, lol. I have pushed it a time or two but thats an exception. 

[speed craw]

No check engine light ? You mentioned you chane the spark plugs regularly.  Those are recommended every 100k miles not routinely.  If your using the wrong parts this could have an effect on the engines perfomance and fuel economy.  I would need more information such as milage , parts used etc .

[I.rar]

No check engine light is on. 

I've replaced them once with pre-gapped oem plugs when I bought the car with 50k miles. I've never waited until 100k lol. I don't think I know anyone who has either. 

What I meant was that is part the maintenance I do to my cars when it's due. 

[flyfisher]

Your right foot is likely the culprit....also it is pretty rare that any vehicle will get exactly what they say you will.  

Seems like everyone else already listed the stuff to check so i won't reiterate their comments but one other thing to check is to make sure your odometer is calculating mileage correctly.  A change in tire size can impact the odometer and subsequently your mileage calculations.

 

[tipptruck1]

2 hours ago, flyfisher said:

Your right foot is likely the culprit....also it is pretty rare that any vehicle will get exactly what they say you will.  

 

 

I know were you are coming from. On the hwy I can get about 35-40 mpg. As long as I stay out of the boost, and stay below 2500. In the city I am lucky if I get 15. I know that is bad. Due to how low the turbo spools up. I usually have 5lbs of boost built up. Just slowly taking off from a stop. Brand new my car was rated at 19/28.

[Fishing Rhino]

6 hours ago, tipptruck1 said:

I know were you are coming from. On the hwy I can get about 35-40 mpg. As long as I stay out of the boost, and stay below 2500. In the city I am lucky if I get 15. I know that is bad. Due to how low the turbo spools up. I usually have 5lbs of boost built up. Just slowly taking off from a stop. Brand new my car was rated at 19/28.

Did you ever get better city mileage, or has the 14 - 15 mpg city been what you have been getting from day one?

[I.rar]

10 hours ago, flyfisher said:

Your right foot is likely the culprit....also it is pretty rare that any vehicle will get exactly what they say you will.  

Seems like everyone else already listed the stuff to check so i won't reiterate their comments but one other thing to check is to make sure your odometer is calculating mileage correctly.  A change in tire size can impact the odometer and subsequently your mileage calculations.

 

I don't think it's me. Around town I usually have my daughter and very rarely exceed the speed limit. I don't 'race' around either. 

The tires were replaced with the factory size and speed traps confirmed my actual speed. 

I know the rated stats are just that but I got better milage in my '96 blazer with the 4.3l and my wifes rogue is getting 20+ mpg and has the same motor. 

[James Pondscum]

  First thought front o2 sensor.  They are recommended for replacement at over fifty thousand miles. You could pull it out and wash it with soap and water no solvents "".  Dealers do this to get them past warranty .As they get old they tend to react slowly.  Also check air intake for blockage.  Rodents etc. to intake.

[tipptruck1]

10 hours ago, Fishing Rhino said:

Did you ever get better city mileage, or has the 14 - 15 mpg city been what you have been getting from day one?

I don't know about day one. I bought the car used, and it was 3 years old by that time. I can say for the last 7.5 years. It has been getting that. I have thought about a putting on a bigger turbo. So that it would start to spool up at about 3k instead of around 2500. Although it has gotten a bit better over the last year or so. I have a feeling it was because I had replaced a cam positioning and crank positioning sensor. Here is were the funny part. I can head over to my family's during the holidays.. They live 110-120 miles away. I can go there and back on just under half a tank of gas. Granted its all hwy, and 100 miles of it is 70mph. The other 12-20 are 55.

[Fishing Rhino]

I was just curious as to whether or not, you had a decline in city fuel mileage, or it has been this way since you got the car. 

I used to love working on cars, but since they have switched to full on computer control they went beyond my capacity.  Back in the day, you could pull things apart.  If the points were pitted you replaced them.  If the distributor cap and rotor  were shot, you could tell by looking at them, and then replace them.

No more points, condensers, rotors and caps.  Heck except for the wires that come out of the coil packs to the spark plugs, ignition wires as I knew them are now a thing of the past.

They are now too technical for a shade tree mechanic. When a fuel pump when bad, you'd go to the parts store and get a kit which included a diaphragm, and a few other parts.  Remove the fuel pump, undo the bolts to separate the two main body parts, replace the diaphragm, and other components, bolt it together, and you were back in business.

Now the things monitor air temperature, air flow, and regulate the fuel injectors accordingly while determining throttle position.

Having said all that, I would not want to return to the good old days when cars were made of solid steel and other metals.  If you got a hundred thousand miles out of a car that was exceptional.  Today's cars, with proper care and maintenance can be expected to do two or three times that.

Problems are a rarity.  Exhaust systems last the life of a car.

I don't understand 'em like I used to, but I like today's vehicles better.

[tipptruck1]

3 hours ago, Fishing Rhino said:

I was just curious as to whether or not, you had a decline in city fuel mileage, or it has been this way since you got the car. 

 

I don't understand 'em like I used to, but I like today's vehicles better.

Like I said its been that way since I have gotten the car. I am really not complaining.  I do love the car when it works right. Having 270hp under my right foot. In a car that doesn't even tip the scales at 3000 lbs is fun. I have even spun the tires in third. Granted that usually happens when the tires are cold, and i am pulling 15lbs of boost. While I am getting on the hwy.

 

As for the second part. My dad and his friends went through the muscle car era. As munch as they loved there gas guzzling 4 barrel carbs. They didn't miss having to mess with them all the time. I grew up with turbo charged 4 or six bangers. They thought it was interesting how a little 2 litter motor. Could make as munch hp as the old v8s. That were 4 times the size.