Hey there,
I have 2002 Infiniti i35 with 132,000 miles

I get about 16 mpg,
I get low gas indicator when I reach only about 240 miles after full tank

I changed sparkplugs, checked air filter, checked tire pressure, tried fuel injector cleaner

I don't have SES light and so I was wondering, it sounds like I may have bad oxygen sensor, but do SES light has to be ON if the oxygen sensor not working well?

Why do you think I might have such horrible gas consumption?

 

go to advance or autozone and have them see if any codes are pending...do you have a skipping or anything?

 

Is it possible to have codes even if it doesn't show SES light?
What do you mean by skipping?

 

from what i've read, yes...hence 'pending' codes...and when i say skipping i mean a misfire..

 

I used to have misfire on cylinder four, I changed ignition coil and after that it disappeared. By the way, I think the problem started when I changed 3 front spark plugs, but it may be coincidence

 

clean your throttle body....i did that on my 01 max with about the same miles as yours....helped a little

 

you might want to make sure about that...i've heard bad things about cleaning your TB on a 3.5

 

glad i didnt do mine yet

 

why is it bad to clean TB?
I brought some cleaner where I need to spray in the maniford from intake and at same time have about 2000 RPM
Also I brought Mass Air cleaner

I went to some good transmission repair place and I spoke with mechanic regarding my problem, he used OBD scanner to see if I have any pending/hidden codes and did not find any. He was clueless on what could be the problem.

I don't think that the problem is in stuff like dirty TB, manifold or anything else because I am getting 16 MPG instead of about 21 MPG and thats a HUGE Difference

 

I would definitely do the O2 if you haven't already. Its probably bad or close to it, if it has 132k on it.

 

Thanks, but do you think I must have SES light for O2 sensors? Or they might be bad without SES light?

 

I replaced one O2 sensor and will do second one today.

Here is the picture of the first old sensor, does it look bad?

 

Looks crusty. That's for sure.

 

Because it is electronically controlled. You will need to recalibrate the TPS . I also highly doubt that a dirty TB is going to make you loose that much MPG.

 

I would suspect a vaccum leak or something along them lines if no codes or ghost codes are being thrown

 

Thanks, what do you mean by recalibrate the TPS? I changed both O2 sensors, the one by firewall was pain in the ***, I think I bend the old sensor a little because it is really rusty there and really hard to get. I will let you know the results as soon as possible.

 

K i maybe wrong about the recalibration. But i know if you have issues after cleaning the TB your suppose to reset the ecu or something along them lines. I found a thread that maybe pretty imformatible to you

http://forums.maxima.org/5th-generat...ly-yes-no.html

and this post sounds like the most reasonable way to clean your TB

http://forums.maxima.org/6856217-post40.html

Good luck. Im a 4th gen guy so i only know so much about the 5.5 since ive done a 3.5 swap. I dont know much about electronic wise with the 5.5 gen

 

If your oxygen sensor has gone bad, it will throw a code. A bad O2 will kill your gas mileage, but it will also throw a CEL.

Is this 16 mpg in city or highway driving? How hard do you drive your car?

I know that even when my car is running 100% I can still get as low as 18 mpg in mostly city driving, but I drive pretty hard. I don't think a dirty TB will kill your mileage like this, although it might lose a few HP. If you were the one to install your spark plugs, are you sure you tightened them down to the correct torque specs?

 

I changed front 2 o2 sensors and mileage now even little worse. I got 15 mpg. Today I cleaned MAF sensor and will see if its going to help. I changed the sparkplugs by myself. I put in platinum +2 sparkplugs. Advanced auto parts said I don't need to gap them. Can you tell me more about torque specs? I just tighten up without any specs and as I mentioned earlier, it seems that the problem started after I replaced front 3 sparkplugs

 

hmm, I'm also having a similar problem except mine isn't as extreme. I was getting 17.2 MPG for months but, keep in mind that I mainly drive in the city. I found out that I was over due for an oil change but, that only brought me up to 17.3 MPG. When I think about it, my gas milaege changed when I added an air intake and throttle body spacer. My sensor was reset and it settled at 17.2 MPG. I thought I should get better gas mileage? BTW, I don't race the crap out of my car anymore. So, that's not why my gas mileage is low.

 

Did you change the 3 rear plugs as well? Could be a faulty mas. I don't believe it will throw a code.

 

Yeah, all 6 plugs are changed.
But here is what I thought.
I have Bosch platinum +2 plugs and I read somewhere that there might be some problems because Bosch is not very compatible with nissan/infiniti. I ordered 3 NGK plugs and we'll see if it's going to help.

Has anybody heard about bosch been not very compatible?

 

Little update.
Cleaned MAF sensor and still get 15.5 mpg
Today I replaced front 3 spark plugs with OEM NGK ones
we'll see if it will help. Other 3 are on the way

 

Does bad knock sensor trigger SES light?

 

I just ordered knock sensor on ebay for $30
You think its good?
http://cgi.ebay.com/ebaymotors/ws/eB...m=370485524639

It says its made in Japan

 

is this possible with a 99 I30t manual trans as well? i think im getting crap MPG but i went from a 1.9l 4 banger to this and i seem to only get about 210 miles out of a tank. and with $50 bucks of premium only getting me a lil over 3/4 of a tank on my last fill up, thats no good.

 

How long have you had your car? If you haven't had it the spring/summer then it may be weather related. I was getting about 200 miles per tank over the winter with primarily city driving. I'm guessing it's because of the number of short trips I was taking while also using the defroster, seat heater and heated steering wheel. When it's warmer (or when I'm at least not using the heated seats and wheel) I can get 450 miles out of a tank purely on highway driving. The difference is surprisingly huge.

 

= (

 

no bueno

 

Winter driving takes a bite out of fuel economy. Mine drops by 12%-13% in the winter months.

 

Well I live in Florida so no winter for me

 

How are you calc mpg?

 

i calculate mpg thusly: trip odo / how many gallons i fill up. if i was a stickler for checking my mpg, i would have a log book, but im not that guy lol. my mom has done it on every car she ever owned. that way she can see if she gets a big drop in mpg that usually means something is wrong.
ive had the car for almost a month now, and i do only work 5 miles away and the bar is about that far aswell, so yeah lots of short trips. hopefully this monday when i take a 2 hour trip to pick up parts for my el camino itll be better.

 

I have a 2002 I35 with about the same mileage. I just bought it about 2 weeks ago. So far I am getting about 28 mpg on 80% highway, 20% city.

Here are some thoughts.

Definitely gid rid of the Bosch plugs(they are crap). I also have an 00 maxima. It had Bosch plugs in it. I put the NGK Iridium IX plugs in and it made a big difference. Make sure you get the right temperature spark.

Do you have any mods to the air intake or manifold or are they stock? Have you seafoamed the intake or had injectors cleaned?

Considering the mileage and no codes, I'd be pretty concerned with a bad MAF, not just a dirty one.

If you have done everything you can think of to the engine and believe that it's running as good as it can, you may start considering problems with you rolling resistance.

I assume your tire pressure is good. Dragging brake calipers can definitely hurt your mileage. When was the last time you had an alignment? It won't make all the difference, but if you are out of aligment, you can really hurt you mileage (along with wearing out your tires fast). Tire type can make a difference also.

Just some thoughts.

 

Thanks. I dont think its maf because i dont have any performance issues. Just the gas mIlage. Does vacum hoses trigger SeS light?

 

well i filled up with premium the past two tanks and my mpg has gone up 70 miles per tank. i was getting around 17mpg filling up with regular and now im getting around 19.5 mpg. yay premium! Boo gas prices!

 

I don't get that difference from premium, may be .5, but no more

 

You think it will be good idea to take the car to infiniti for diagnosis? How long do u think its gonna take them for diagnose the car? They charge $120 hour

 

I went to my friend that had good odb tester and diagnostic tool and it revealed that I have problems with ignition timing advance #1. You think it could be problem to my gas milage? anybody knows how to fix it?

 

Also it showed that I have problems with two O2 sensors
B1S1 and
B1S2,
I recently changed B1S1, so you think there might be something that affects both of these sensors? if both of them are B1