12-14 MPG Average?????
 

So I had a bad misfire issue and what not for about a week (p0300) and other codes saying my bank 2 was running lean. Had it diagnosed and changed out the bank 2 side MAF sensor. Ever since then I can't get higher than 12-13 Mpg on average??

Can anyone please help or share some advice on the matter? I'd like my 20-23 MPG back lol.

I'd check the oxygen sensors.

How would one check the o2 sensors without having to buy new ones?

Get an OBD/CAN monitor and watch the O2 values.

Will do!

I'd freak out w/that fuel mileage....still 24 & up consistently/ after mods....down about 1-1.5 from stock.

May need a fresh set of plugs; as the lean condition created a lot of extra heat,,, bank 2 (being the drivers side) gets air from the passenger side throttle body,,,you must have had a vacuum leak or dirty air entering to KO maf?
Also don't rule out a weak or failing fuel pump.

Only have about 45k miles on the car. Ill change out the plugs and see what happens.

And thats odd, I changed out the driver side MAF sensor. Also the codes were telling me bank 2 was lean. Thats the same side?

Bank 1 is the right side (passenger side on US models). Bank 2 is the left.

I know the bank 2 is driver side, but I also changed the MAF sensor on the driver side intake. He is saying they are backwords, so how did that fix my issue if the MAFs are opposite of the banks?

I wasn't considering a right handed steering car when i said "Driver's side was bank 2"

Cross-Ram intake manifold.

Ah. It sounds to me like he's saying that the Bank 1 MAF is measuring air going to Bank 2 cylinders, so a bad B1 MAF would lead to an improper mixture (and corresponding O2 readings) in B2 cylinders. I'm not sure if that is true or not (or how it would affect your engine), but jchammond is pretty reliable.

Unless you have run terribly rich in the past, spark plugs shouldn't be a problem at 45k miles. I'd check a few of them before deciding to replace.

Have you had the upper plenum off, or installed a CAI recently? the po300 random cylinder misfire could be any different one.....or did it say cylinders 2,4 & 6 only (bank 2 cylinders) ?

Anyways, Yes ill buy 6 new plugs and the Z1 fuel port to check my pressure and go from there. Also check my o2 sensor values. (Not sure what they are supposed to read though)

Berk HFC and AAM short tails but they have been on there since like 20k miles and the issue just started happening. Once I changed out drive (US) side MAF sensor, all the problems cleared. But now I have horrible gas mileage.

Here's an intake pic,,,not oem- but you will see how air flows.http://uploads.tapatalk-cdn.com/2016...346a05515b.jpg


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You also don't want to just start changing parts to see if it corrects problem w/fuel milage,,,As SouthArk first suggested to test values of O2's & run a test....would be first step...I'm not sure if you had your ~Z~ Tuned,,,but a re-tune on Dyno would definitely help.

Just seeing you have HFC's,,,hopefully they are not clogged/damaged.

Update on it, 8 took it to get the codes pulled again and it's still saying bank 2 running lean.

Probably stupid comment but you did reset the ECU to get rid of the codes afterwards right? :)

I have no idea why kind of mileage I get, except that it's going to get a lot worse lol

Update on this and my misfire issue. It was all due to a bad CRANKSHAFT position sensor!

How much is the part and how difficult to replace?

From the Nissan dealership it cost me $188.?? and it wasn't to bad but was a very difficult spot to get your arm and ratchet in.