01 maxima ae with milage between 12 and 16

[bennuss]

I am at wits end and considering selling the car. I am getting 12 city and 16.6 highway. I used to get 23.5 highway and I was using regular gas. I cant seem to find anything wrong. Should I put in new o2 sensors even though I am not getting any code? Also the maf is only 6 months old and the car seems to be running smooth. Any other sensors I should look at? The car has 145,000 miles no codes.Anybody see anything that would be the cause?

[bennuss]

Does anyone know what the normal fuel flow rate should be?

[Fezzik]

Wow. That is bad. My first thought is the o2 sensors giving bad readings saying the car is lean and giving it more gas.

[bennuss]

Are there any numbers there that seem off?
Can you help me with which o2 sensor to buy from rockauto. I assume its the upstream ones that i need. I looked and their seems to be multiple different ones.
Also someone said to me about buying a universal bosch with is cheaper and wiring it. I know electrics/electronics so should not be a problem for me just need to know the item numbers i should buy. thanks

[loystock]

Ensure you don't have a vacuum leak nor problem with ignition. Normally, a faulty O2 sensor will generate a fault code. As for the MAF sensor, did you buy OEM?

The O2 sensor normally swings from 0.2V (lean) to 0.7V (rich) with mid-point of 0.45V (ideal fuel/air ratio). From the info you have provided, Bank 1 Sensors 1 (front) and 2 (rear) are reading very low with an average of @ 0.2V. This tells the ECU that you have a lean mixture and thus more fuel than necessary is being fed to the engine. I didn't see the voltage from Bank 2 sensors.

FYI, Bank 1 is the right side for cylinders 1-3-5 (towards the firewall) while Bank 2 is the left side for cylinders 2-4-6 (towards the radiator). There are 4 O2 sensors with front and rear mounted in the pre-cat (there is no sensor in the main cat, unlike the earlier Maxima/I30s). There are 3 connectors near the radiator (red, white and blue harness) and one connector (black harness) on the rear pax side near the intake manifold.

I usually go to IoS (Infiniti of Scottsdale) or Sparkplugs.com to find out the part number and pricing of the O2 sensors. The OEM Bosch sensors are expensive, usually over $100 so I use the equivalent NGK/NTK. You can also get it cheaper from Amazon provided you know the part number you are looking for and verify it fits your car.

[bennuss]

I am assuming that I need to change all four or just the upstream ones( the ones before the cat) which would be b1s1 and b2s2
How would I check for a vacuum leak?

[loystock]

For Bank 1, yes, both of them. For Bank 2, I don't know since you did not provide that data. If you are going to do it yourself, better buy an O2 sensor adapter ($10-15) to facilitate sensor removal/installation and avoid damage to cable.

Check for obvious sign of leak from the air filter box all the way to the throttle body and IACV. There are several vacuum lines there. Spray suspect area with carb cleaner and listen for slight 'surge' in RPM.