zook1977

The gas mileage on my 1999 Nissan Maxima GXE has droppped. I used to get about 26 miles to a gallon, but now its dropped to about 21. I changed my fuel filter, cleaned my fuel injectors, but still no improvement. What could cause this drop in gas mileage???

Colossus

iTrader: (1)

One possible reason is the switch to winter gas blends. Check your tire pressure and air filter since you already changed the fuel filter.

Nismotic

iTrader: (25)

check out the stickies for some helpful info. also, do a search through google including maxima.org in the search, and it should pull up the 1 billion threads on this.

jbreit

Assuming you have no engine codes, I would also blame winter gas, and the longer warm up time your engine has in colder weather....especially if it sits outside overnight.

Just thinking out loud, there could be some other rare mechanical issues...bad wheel bearing(s), sticking brake caliper, alignment problem. A bad coolant temp sensor would throw a code and have other problems around it, as would an EGR valve. Knock sensor may be on the way out, and that will not throw a code.

I am assuming your other maintenance is up to date....plugs, tranny fluid namely

Those are the only idea's I have....
good luck.
JB

Batxel

iTrader: (1)

check your ecu codes, check tire pressure, bad o2 sensors can cause bad gas mileage. People have said that the knock sensor can cause bad gas mileage, but doesnt trigger the check engine light.

Broaner

iTrader: (10)

You lowered? Have you bottomed out lately? Get on the ground and check that your rear o2 is intact. That sensor has been the culprit of my bad fuel mileage three times.

zook1977

Yes I did bottom out recently. Which is why I changed the fuel filter. Anything else I should have done?

njmodi

iTrader: (4)

Broaner - I thought the rear O2 sensor didn't contribute to the air/fuel mixture... i.e. didn't affect mileage.... assuming rear means the one near the cat.

NmexMAX

iTrader: (22)

Why would bottoming out require the changing of the fuel filter?

njmodi

iTrader: (4)

Maybe he interpreted it as "bottomed out the fuel tank" so he may have sucked crud into the lines/filter...

zook1977

I did think he meant the fuel tank. Does it mean something else?

njmodi

iTrader: (4)

I think he meant, "did you drive over a speed bump/curb/object that bumped the under-carriage of your car?" - which could have potentially damaged your O2 sensor... but as I had already stated, the O2 sensor that could potentially damanged by such an event doesn't affect gas mileage (the one downstream from your cat).

NmexMAX

iTrader: (22)

Yeah leave the filter out of this...