Nissan altima 93 125000 m gas mileage very bad

[catkoot]

Nissan altima 93 125000 miles

I did tune up cost me $250 .Still the gas mileage 14 m/g local why?? Is thats

right! should i buy new car better. I make around 150 miles a week .

[methodmix]

When you say "tune up", what do you mean exactly? What exactly was done during the "tune up"? New spark plugs are usually a given, but for $250 I'm guessing they cleaned out your throttle body and injectors as well, but if not then you got ripped off. Another common issue could be a bad O2 sensor (usually your engine light will come on for this), a dirty Mass Airflow Sensor. You might also want to check to see if your air filter is clogged, but this should have been checked during the tune up. That should be enough to get you started. opcorn:

[catkoot]

I guess the tune up that was done, the spark plugs and wires, air filter, gas filter, distributor cap ,oil + filter change ...
Any way the check engine light is not on . could it be sensor 01? !! Should i change them any way 01, 02 ?!

[methodmix]

With the amount of miles you just mentioned, you definitely need your throttle body and fuel injectors professionally cleaned. If your engine light isn't on, your O2 sensors should still be okay. Another thing you might want to have checked is your compression and ignition timing. If your timing is retarded, your engine will run more rich causing bad fuel economy, but this also results in incomplete combustion in your cylinders which leaves behind carbon deposits. Carbon deposits are bad for your fuel economy because they create extra friction in your cylinder walls, which means your engine has to work harder to achieve the same performance. If your compression is higher than what it should be, that is a good indicator that you have carbon deposits. It's a vicious cycle so you really need to get this checked out soon!

[mckinney_noel]

it might be a knock sensor going bad or is bad