I've had my 00 since it had 30K on it. It currently has 145K on it. I've always gotten about 370 miles to a tank. Actually, I believe I got about 330 prior to the intake and cat, but for as long as I can remember, I've gotten 370.

In any case, it recently went to hell and I'm only getting about 300. I had a coil go bad, so I replaced it. I also replaced the plugs as the mileage seemed to be bad after I replaced the coil. I figured the plug got fouled and I was due anyway. I had already replaced the plugs ~ 90K with Bosch, but wasn't too impressed. I went back to stock NGKs.

So...what gives? With today's gas prices, this really sucks.

My check engine light has been on for about 100K. I scan it and reset it every couple of weeks. Its an O2 sensor code and I know that those typically cause MPG decreases. However because I've only had this issue ever since the coil, I don't believe it to be the culprit.

I have also had a couple of tanks where I got closer to 370.....seems like only when I fill up at BP. Perhaps my car will now only run on 92 octane???

 

If you got an O2 sensor code, it's most probably the reason for the decrease. Whenever these pop up, it's usually a sign of them going bad and then completely failing. In fact, I had one pop up on me last week (front 1, bank 1). I cleared the code, but ever since this code popped up, I noticed my gas mileage went down. The code hasn't reappeared since then, but I know for a fact that it will come back. I have the sensor to replace it, but I am just waiting for the weather to get more warm. Until then, I just have to suffer!

 

the o2 sensor is what senses the fuel trim level, so if it is bad you will get bad mileage.

 

Depends which sensor.

 

The only reason I'm not all over that O2 sensor is because the light has been on for over 100K miles. I've only been getting bad mileage since the coil went bad.

 

You don't have any misfire code or anything associated with a bad coil, so you need to eliminate the obvious first. If you have a o2 code on a front sensor, your engine is not making any fuel trim adjustments.

I don't don't know what kind of setup you have on your car, but did mention something about a cat. Could there be a clog?

Also, please check your MPG by getting a fill-up and zeroing out your trip meter. Then the next time you full up, divide the miles on the trip meter by the number of gallons it took for the new fill-up. That will be way more accurate.

This per-tank number you're giving us is a guess at best.

 

. You mean the ECU isn't.

In some cases, the ECU will refer to the secondary O2's.

I don't have any primaries on my car, and still get 26 MPG highway in my 03, which are all Calispec. ( 2 primaries/2 secondaries)

 

Yes, pardon my misstatement. I now see why you have over 16k posts.

 

I couldn't tell you the MPG off the top off my head, but I do calculate every tank and its down a few. I believe I get 23-24 usually, and right now I'm around 20 - 21.

I have a Random Tech cat - how could I tell if its clogged?

I understand that I should replace the O2 sensor, but I'm still not convinced that is the cause of the issue. I was getting 23 - 24 mpg....coil goes bad so I replace it and all the plugs...instantly now I'm getting 20 - 21 mpg.

 

16K posts! Holy ****!

 

damn these o2 sensors sucks major a$$.
My frikkin mpg is averaging at 250 to the tank.
14mpg avg

I get engine check light and I was told last summer that its pulling up o2 sensors. didnt chenge em yet but it looks like itll be a *****.

So far I changed PCV valve , Fuel filter, engine flush, trans flush, spark plugs + full tuneup in november. The muffler is rusting and is on brink of falling apart, with bees in a can and all. Oh yeah, my suspension also sucks a$$. Now other than that and the MAF that i got from a junkyard, what else could be culprit to SH*TTY mileage. Is it the O2s most likely???
Cuz after reading 4 pages of O2 madness, cost, and confusion incl. Im wiggin the f*ck out like wtf!!

o2 confusion link:
http://forums.maxima.org/showthread.php?t=312876

 

i'm thinking O2 sensor

 

get o2 here while u still can:

http://forum.maxima.org/showthread.php?t=529259


.

 

So true. When I got the CEL, I got only 300miles/tank. After a reset, I got back up to 400miles/tank. My CEL pops on every few other weeks too. I'll probably Seafoam then replace o2.

 

Coool. Thnx for the link also. Gonna go get those check engine codes again for the part #s.