what's up guys, just signed up so I can ask some questions. I just bought a 03 sedan at 136k. when I first bought it the thing was getting 11mpg everywhere so I did a tune up aired the tires to 45 psi changed plugs to some good plugs changed the pcv valve cleaned the maf sensor tried a fuel cleaner and did premium gas this helped the car get to 15mpg hwy. I did a ecu reset and air control valve recalibration this didn't do anything. now before anyone says its the way you drive understand I grannyed this thing after resetting the ecu im talking no more than 2k rpm anywhere.... please do not post its your driving because I know its not. I'm considering getting a programmer or a ecu tuner I've owned a 03 g35 before and it got 20+ even when I hauled *** everywhere. now this car only gets about 70 miles out of $20 I can't afford to drive 45 miles to work and 45 miles back everyday I'm going to go broke. does anyone have and real suggestions about what could make this car use its factory gas mileage. it doesn't have any cel's, sel's. it drives great! lots of power. smells a little rich sometimes but I know these cars are tuned rich factory. remember I granny this car please no posts about driving habits Dont waste my time or yours with the useless tip every gas mileage thread gets hijacked with this.

 

Have you replaced the o2 sensors? If not you could try that.

 

hmm, usually o2 sensors will throw a code if they are bad. the car was first bought in cali. i wonder what extra things they put on it for emissions. anyone got a idea?

 

O2 sensors throw a code when they fail. When they are dying they dont and can hurt mpg.

 

the car has 4 of them right?

 

Right. On a negative note, it could also be failing cats with that mileage, (especially if the previous owner(s) ran regular fuel). A check of the entering and leaving exhaust temp. from the cats should give you an idea.

 

Sedan can run regular so I doubt that would matter. However, if you are burning oil that will kill cats quick. How much oil do you burn between changes?

O2 sensors arent cheap, but cheaper than cats. I would try those first then cat. Things that clean carbon can kill o2 sensors. If too much carbon is cleaned and leaves it can deposit on the o2 sensor damaging it. Stuff like seafoam and the like.

Fyi my car has 190k miles or so and has original o2 sensors and cats. In fact everything is original in the drivetrain except fluid, belts and plugs. I drive 33 miles one way 4 days (264 miles)and have a little over 1/4 tank left at the end of the week. Not sure why cats would go out at your mileage unless you burn alot of oil. O2 sensors I could see.

 

Please tell me what the sticker on your driver door jamb states for tire PSI inflation.

 

the car does have 4 but only the front matter. So just get the front 2, they effect the AFR the most.

So you went from 11mpg to 15mpg , what is your end goal? Keep in mind these cars are gas hogs on some of the more extreme levels. Best i ever got was 23-24 pure highway cruising at 70mph with A/C on. But i nomrally average 18mpg. But when my GF drives the car she averages 16mpg, even tho she doesn't drive it hard. She doesn't coast to lights, thats all i noticed. I'm not saying your driving is bad.

I also think being that your a 2003, you might have the OLDER ECU which is not able to be modded and that can cause lower MPG.

Always scan for codes, make sure to check pending faults. I dont think there is much you can do. Check your brakes as you might have a dragging/stuck caliper or sliding pins. Make sure you dont have a 200lb sound system in the trunk.

You might just have to accept the 15mpg.

Also this is KEY here, how are you calucating MPG? I wont say what the right way is until you answer it.

 

That sounds about right if it's canadian gas prices,
But another +1 on the front O2 sensors and maybe even the air filter.

 

+1 on O2 sensors. Wheel bearings okay?

 

Since my 04 sedan has averaged over 21mpg overall in it's 111,000 miles, he should be getting much better for highway mileage. Obviously, what the problem is is the question

I even got over 29mpg once on a road trip over 500 miles back in May. Now, that was just the once I got that high. But even high mileage can do well.

 

You have to determine the condition of the engine. If the engine has burnt exhaust valves, (not that uncommon on high mileage engines) you're losing efficiency. If you car is burning oil (loss in compression) you're losing efficiency.

Buy a leakdown tester at HF and see what condition the motor is in. The car doesn't run rich from the factory. Maybe when the throttle is pegged the fuel trim riches up but these cars have dual A/F sensors (AKA wideband o2) to monitor fuel trims so it's unlikely nissan wouldn't tune the engines for maximum efficiency.

If you are satisfied with the condition of the engine, the next thing I would do is have the fuel injectors cleaned and balanced. People are pinching pennies at the pump and put in the cheapest gas they can find. Some people say, those cheap gas stations use fuel with less additives that keep your injectors and intake valves clean. Clean injectors and valves are important for good fuel efficiency.

You can also get a scanner with live datalogging capability and check your fuel trims. Specifically, your long-term fuel trim correction. If you have a high + correction % that could be indicative of mechanical problems. Your fuel trims can also tell you if you have a vacuum leak before the ecu triggers a fault code.

 

I also want to add, you should check your engine coolant temp (ECT) on a scanner. If you ECT sensor is reading too cold, you're computer can be in warmup mode which uses a richer fuel mixture. Your car should be running at 175+ degrees once fullly warmed up. If it's any less, you have a bad thermostat or a bad ECT sensor.