Okay, I use 91 octane, the highest I can get out of a pump from where I live. I have heard that the loss of gas miles per gallon is because of bad O2 censors. Is this true? Because I am averaging 20-23 miles per gallon, is this right? It doesn't seem like it. Are there any other leading factors as to why I am getting bad gas mileage?


~Thanks

 

Is it cold where you are ?? The car works alot harder and uses alot more gas during the winter months becuase of warm up.

I dont even test my milage durine the winter due to Oxegenated gas causes 3-4mpg less and I warm my car up alot before I drive it. Sometimes at work ill go out 15 min before I leave to warm it up for the short ride home, and when it snows, forget about it...I leave my car running the hole time I shovel

-matt

 

bad O2 sensors, knock sensor, FUEL FILTER or fuel injectors. Do the easy cheap stuff and then do the injectors if nothing else helps.

 

the mileage difference is really that drastic huh? i went from 22-20 to like 14 or 13 now, bit ridiculous, but i did warm up significantly more than i usually did this week. im obviously having the same problem, just wanna confirm that the knock sensor is the culprit, gonna move onto the fuel filter, bothers me if my car isnt operating at peak

 

Well first you need to check what IS wrong. The fuel injectors are really easy to find and check, the fronts at least. The KS isn't that hard and the O2 sensors aren't bad either but you need to remove them to really check. I replaced my KS and it improved a bit. Unfortunatelly with the winter here the fuel economy is back where it used to be before the KS replacement.

 

Octane here is, 85, 87, and 91. Would it be alright if I use 87 octane? I currently fill my tank with 91, and I know that's good, but would it be safe to run with 87?

 

How does a faulty O2 sensor have a negative effect on fuel economy?
My fuel economy severly decreased but i thought it was b/c i switched from synthetic oil to non. i guess i need to check my o2 sensor too now.

 

"1) Air filter. The stock filter on the car is a drop in panel filter. If you bought your car used there is a chance that the filter may have never be changed. This would be the time to do it and you have several options: drop in K&N filter, cone filter or CAI. A search on any of these terms will resolve any questions you may have. If you have a cone filter, the filter may be dirty. K&N makes a recharge kit that is available at Pepboys to clean the filter.

2) Fuel filter. The fuel filter is small gray cylinder on the back of the firewall that is to be changed on a 60k service interval. It is often to blame for bad gas mileage, but can be a pain in the butt to change, but it can be done. The filter is relatively cheap from Nissan. Some members reccomend buying a fuel filter for a Nissan 300ZX. Its the same size hoses, but twice the size, so it lasts 2x longer and is doubly effective. The choice is up to you. The writeup to change the filter can be found here: www.maximadriver.com

3) Spark plugs. If you're running anything other than NGK plugs in your engine, or you bought your car used, go get some NGK spark plugs for the dealer. Spark plugs are to be repalced every 60k miles, but rarely are. They will cost about $10 a pop. Sprintmax has a great spark plug changing writeup that can be found here: http://www.sprintmax.com/tails/sparkplug.htm

4) Dirty throttle body. The throttle body is the first piece of metal behind the intake system. It accumulates a certain amount of dirt and grime. Those who clean it out after long neglect find their car is smoother and that fuel economy does increase. Writeup can be found here: www.motorvate.ca

5) Tire Pressure. Stock tire pressure is 29psi. I found recently that mine were at 25 and filled them up and found a substantial increase in fuel economy. If your tires are low, go ahead and fill them up (I filled to about 31, but everyone has a preference).

6) Oxygen sensors. If an oxygen sensor is messed up, it will trigger a Check Engine Light. There are three sensors in total. 2 rest in the respective branches of the Y Pipe (these are the Front Heated 02 Sensors) and one rests in the catalytic converter (95-96) or in the B Pipe right behind the cat (97-99). If any of these sensors fail, gas mileage will decrease substantially. Many sites exist that sell oxygen sensors (dealers will charge a lot). www.buyoxygensensors.com gets good reviews on this site frequently, and they have good prices. For a writeup, go to www.motorvate.ca, or search around the .org

7) Knock Sensor. This is the bad boy, the code everyone fears. The sensor is actually just a piece of metal that rests under your intake manifold. They cost approximately $110 from various sources (www.thepartsbin.com is usually cited as one of the best). The sensor is not terribly difficult to change, but as my friend Harold described it, "Nissan must weld razor blades under the manifold." Due to tight fitting, the sensor often results in a bloody hand. The writeup for the sensor can be found at www.motorvate.ca

8) Dirty fuel system. As a car grows older, carbon deposits in the fuel path, clogging areas such as the injectors. Many modern gasolines are designed to combat this (such as Chevron with Techron) and there are many additives that can be added to gas to clean out these systems. Many mechanics offer a full fuel system clean out for about $50-$75. Many .orgers believe this to be BS, some think the process is valid. The choice is yours."

copied and pasted right of the FAQ section of the forum

 

I appreciate all your help and replies.


Thanks again.

 

I am averaging 19mpg and i thought it was normal, because when i had 4 cyl Nissan 240sx i was averaging 25mpg

so whats normal then?

 

Manual: 22 mpg / 27 mpg
Automatic: : 21 mpg / 28 mpg

 

The rear O2 sensor doesn't affect fuel economy.

 

stock tire pressure is 29psi? geeze when my shop put my new tires on they filled them up to 44psi and told me if the ride was too bumpy to lower them to about 40. is that correct. should i just leave them 44psi? they're michelin hydroedge btw