Silviet

So my 98 maxima is getting 10 miles per gallon ( I did the math im 100% sure) basically i filled it up full tank using 93 octane ran it till empty and totaled up to 130 miles. This is really bad. There's no leaks whats so ever no smell of gas and its throwing out no codes. I have no idea what the problem could be. I did a tune up on the car when i bought it about a year ago. I've looked everywhere for another post like this and i couldnt find anything at all. Please help me save some money in my pocket

Amerikaner83

iTrader: (17)

how's the performance?

replace the fuel filter. What spark plugs are you using? Also, see if your main cat is clogged, and DOUBLE CHECK FOR CODES. Perhaps you've got some but the CEL bulb is burned out. It's happened before

Silviet

Performance feels fine, fires right up i checked for codes and it says i have none my cel is fine. I've already replaced the fuel filter

Amerikaner83

iTrader: (17)

see my edit re: spark plugs

Silviet

The spark plugs are new with the tune up their bosch iridium plugs

nsnrider

iTrader: (59)

no smoke from the muffler?
any leaks when you fuel up the car?
what kind of neighborhood do you park the car, it's not unheard of to have fuel siphoned out.

calculate your mileage again. is it consistent?

Silviet

I see white smoke from the muffler but obviously its winter here and its cold out.
no leaks at all and no gas smell at all. I'm 100% positive no one is stealing gas. This is the 3rd test I've ran and i calculate every time 10 or 11 miles.

Amerikaner83

iTrader: (17)

get rid of them.

Get yourself NGK Double Platinums if you want to not worry for another 100K. Or NGK copeprs if you don't care about changing them every year.

nsnrider

iTrader: (59)

you might want to rule out the primary oxygen sensors. I've a problem on numerous cars when the o2 sensors failed and sent the computer calling for more fuel, car ran super rich and had horrible gas mileage. Most times it did not set the code. Easiest way to check if its the primaries causing excessive rich condition is to unplug them and drive a bit. You'll get a check engine light t\for the sensors but the ecu will use the default fuel maps and you won't be hurting your car and it should be evident in a short period if the primary sensors are causing the issues.

nsnrider

iTrader: (59)

I second that.

Silviet

do you really think thats my gas problem?

Amerikaner83

iTrader: (17)

it could easily be a contributing factor...along with the O2 sensors that nsnrider mentioned above could also easily be a factor, yes.

foodmanry

iTrader: (15)

Do the O2 sensor test first as described.

I ran iridium plugs for a while and there was no difference in mileage. Plugs can make a difference, but NOT that much of a difference.

clive

Yeah I agree with Foodmanry. I've had Bosch plats in mine for about 30K miles and it runs just great.

Prophecy99

iTrader: (1)

did any one consider how the car is driven.... ? that can be up to 40% of the effeciency

how are u driving the car?

tire pressure? alignment? added weight like a stereo system?

many many additional factors, if everything else has been double checked.

matty

iTrader: (54)

Feel all your wheels after driving, especially your rear wheels. You could have a sticking caliper or two

Matt

foodmanry

iTrader: (15)

Good suggestion...this is pretty common.

Quickywd01

iTrader: (16)

Did you know that a bad knock sensor (KS) will not illuminate your CEL?

asand1

iTrader: (1)

Get the Bosch out and any flavor of NGK in. Also, did you fill it back up and note the amount of fuel, or just assume that the tank is empty? Because I guarantee there was a couple gallons still.

lightonthehill

I'm not on this section of the board very often, and so am not aware of whether I am in the midst of professional technicians or 'every day Joes' here, so apologize up front if I overdo things here.

I'm a little uncertain here. You mentioned filling up your tank and driving till 'empty.' I'm sure you did not really mean 'empty', but maybe the fuel guage was reading near empty. Your MPG can ONLY be measured by dividing the mileage driven by the gallons of fuel required to refill your tank.

I say that because, by going 130 miles and averaging 10 MPG, I assume that means it required 13 gallons to refill your tank? Your mentioning tankful brings up another issue. MPG cannot be accurately measured on one tankful, as there are 46 variables I am aware of that preclude this. I'm sure you are aware that fuel efficiency is totally unrelated to 'tankful'.

IF you did measure accurately, your MPG means something unusual is going on with your car. That is too big an MPG divergence from normal to be changed by the piddling points I am suggesting, but I will list them anyway:

Are you filling up while sitting in the same position at the same gas pump each time, and doing this for at least three fillups?

Fueling at the same gas pump in the same position means the car will have the same front-to-rear tilt and the same side-to-side lean, which means the gas will reach the point/level at which the pump will cut off the fuel at the same relative time each fillup. This is important because our fuel tanks are shaped sort of like mattresses, so a slight tilt or lean can make a big difference in how much fuel gets in.

Doing this at the same pump means the individual pump sensor will cut off at the same point/fuel level. Every pump sensor cuts of at a slightly different point/level.

Adding the mileage driven on at least three tankfuls by the total number of gallons required for the three fillups will give you a very good MPG measurement.

IF, after doing this very careful three-tank routine, your MPG is still below 15 MPG, either you live at the top of Pike's Peak (very steep climb), or you spend your days sitting at traffic lights, or your neighbor has figured out a way to siphon your gas at night.

Of course, if you are a normal driver driving in normal conditions, an MPH less than 15 tells us something of a major nature is not right with your car. I recall my 4th gen 1995 getting over 20 in suburban driving and between 26 and 29 on freeways.

Again, I apologize if I am overdoing this. I'm only trying to help.

njmaxseltd

iTrader: (19)

I agree with the above post. At 10 MPG the fuel consumption is over 2x normal. You should be seeing dark exhaust gasses, a very sooty tail pipe and you should be throwing codes for "system to rich" for both banks.

jtricer1973

I second the advise on calculating the MPG. I could easily see it going up at least a few gallons if not more if you follow his advise.
I also second the advise on the o2 sensor/sensors as I too have had them kill my MPG before, although you did say there were no codes. The last one I had this problem with was a 96ish Altima, can't remember if it threw a code or not.

jasoneon

Tried to post this yesterday with a long explanation but it kept saying I wasn't signed in so I gave up. Could be the coolant sensor. If it's sending a signal to your computer that the coolant temp is always cold the computer will run the car rich trying to warm it up. You'll get the same kind of problems if you were to remove your thermostat.

dwapenyi

iTrader: (3)

Primary O2s especially if you've never changed them before. Coolant temp sensor as well.

Nismo9055

a faulty maf won't usually cause the cel to light up and can have a drastic effect on gas mileage, but will usually be accompanied by performance problems. I agree to check the brake calipers. Do you have any funny noises or sounds while driving? A whining noise could indicate a bad wheel
bearing. Also if your tranny is an automatic, make sure it's going into 4th gear. You could also check tire pressure, but I doubt low tire pressure would
have that much of a drastic effect on mileage...