93 maxima se poor mpg, dirty oil?

[machinehead26]

I just recently purchased a 93 maxima se auto and I've got really bad gas mileage. Its only get about 100 miles per half tank of gas(city driving), could it be a bad o2 sensor? I also notice that my engine oil got dirty a week after changing it? What could it be problem?

[MTZI30]

Bad gas mileage could be a number of things. Any check engine lights? Car running ok? When was the last time it was tuned up. Check to see if the airfilters dirty? Now what do you mean the oil is dirty after only a week? Like it was gold going in now its black? How hard do you drive the car? Miles?

[machinehead26]

180k on original motor,I don't beat on the car ,no cel, car running smooth just replaced all injector and tune up about 1000 miles ago. Air filter are clean, oil was gold a week ago and now its black?

[MTZI30]

Well if you say 100 miles per half tank of gas your prolly using the gauge to measure gas milage. You should get a full tank and run it until it appears empty and see how much gas the car takes and determine your mileage that way. Like me, ill go 300 miles and be a little low on gas and my car will take 15 gallons, so I get 20 mpg. As for the oil being black, ya know if your going a few hundred miles and it looks a darker i wouldnt be too worried, car does have quite a few miles. Sounds like you take care of it though and i can understand you wanting to save some money. Maybe you got a buddy with a smog machine? See how much HC/CO/NOX its putting out? Like higher hydrocarbons could be old spark plugs?

[James92se]

It's likely your 02 sensor assuming it's never been changed.

Then again, a lot of little things can add up to give you less than stellar MPG. Air filter, tune-up, etc.

Also, as was said above, the gas gauge isn't linear, so basing perceived MPG off half-tanks per the gas gauge isn't very accurate. You need to do a fill-up, reset the trip meter, run the tank to nearly empty, then fill-up again and calculate your MPG that way to be more accurate

[Chris92SE]

One thing that sucks about these older Maximas is the lack of information from the OBD 1 computer. Rare to get a CEL and generally, it won't tell you anything until something is already toast.

I would start with the o2 sensor, but another common problem is the knock sensor. Does your car seem to lack power when the engine is hot? That is usually a sign. Knock sensor is a PITA to replace, though.

There are some auto basics that can contribute to poor mpg. Dirty air filter, throttle body, injectors, low tire pressure, a lot of weight in the car.