if you pulled off the airbox and just flipped the butterfly plate up to clean that, then your throttle position sensor is out of calibration. at my dealership, we dont clean TBs that way, at least not on the newer throttle by wire TBs. the only fix is to do a relearn.

 

I have been getting 320 ish per tank (20mpg) since day one? Am I reading that people are getting close to 400 miles per tank?

Doesn't the oxygenated gasoline drop gas efficiency? Chevrons sites lists some interesing info about it?

http://www.chevron.com/products/prod.../whwyoxy.shtml

 

that only applies to the 5.5 gens to my knowledge. Both Whitemax and I have year 2000s with the 3.0VQ.

 

i get 240-260 a tank.

 

You're ideas on heat transfer do not make much sense since as the engine block it hotter its heat transfer is greater to the air and coolant so there is more energy loss from the engine not less.

Actually Carnot theorhetical efficiency says the greater the difference in temperature between the hot resevoir (the mixed combustion temperature) and the cold resevoir (outside ambient air) the greater the efficiency and thus, better mileage.

In real life this doesn't happen but its not because of your theories. Poor mileage due to cooler engine temperature is more of an issue of poorer combustion, a chemical issue, more than heat transfer and thermodynamics.

Especially if you have a stuck open thermostat and the engine is running cool you'll get significantly poorer gas mileage. That's because of poor combustion, not an issue of heat transfer between the engine block and the ambient and coolant conditions.

An additional factor is the higher ethanol content of winter gas, up to 10%. Ehtanol, gallon for gallon has much lower btu content so the more you mix in the less you get per blended gallon. Aslo, in driving through winter slop, there's more drag on the tires, further decreasing mileage.

 

doh! i didnt look to see what year you were driving. im just so used to always working on these newer cars so i automatically assumed, oha well sorry exnay on my informationay

 

The decrease in the winter is not due to refinement, as much as it is due to the increase in use of defrosters, and running idle to warm up the car, etc. I haven't noticed a change in gas mileage (although, I had BETTER gas mileage down south in Louisiana when they weren't injecting it with the ethanol crap like they do in Chitown).

 

WhiteMax,

I experienced a similar problem with my Max. It was hesitating at certain RPM's. I replaced the MAF sensor and the problem went away but car would stall as I approached a stop sign and put the clutch in. I went to Nissan, got the Consult-II reprogram and that helped adjust my idle and allowed the ECU to recognize the new MAF. Please note: from what I've read on the forum, a reprogram is necessary with all MAF replacements. Some guys on here have gotten away without doing it, but in your case I think its necessary.

BTW, my fuel mileage was approximately 20MPG before the reprogram (city). Now I am getting 24 MPG (city), with a 5 sp.

Hope this helps.

 

Actually, my problems started just like yours. My max would also stall upon coming to a stop. After reading through the threads, I decided to clean my throttle body and iacv. I'm pretty sure for whatever reason, that caused my maf to go out. Either it was on its way out or perhaps some tb cleaner got on the maf. Anyway, I ordered a new one from Dave B. and that fixed everything. I didn't bother to do the reprogram because everyone said it wasn't necessary. I had mine reprogrammed the other day, so I haven't really driven it enough to see if has made a difference. Turns out, it was running rich. I have driven 130 miles and the gas hand is between 3/4 and 1/2 tank. So, just by that, I would say that the reprogram after replacing the maf is definately a must even if the car is running normal as mine was also.

 

id say its possible that your car, if running faster, is using more gas with the cold air (cold air is better for mixture...hence the idea of the cold air intake...but less economical) and like the fellow said above, a lot of gas is wasted keeping the engine warm to keep compression correct.

using the climate control will consume gas, especially the heater during winter...at least on my maxima.

 

I think the reprogram took care of it. The tech said that bank 1 was running at 87% and bank 2 was running at 89%. According to him those values are too low and indicates that the car is running too rich.

 

how much do the dealers charge for the reprogramming and how long does it take them?

My gas mileage has gone down after changing the coil packs. I get about 200-220 per tank city driving, about 400 highway.
The needle is on the first quarter mark and I only have gone 45 miles since filling up.

 

WhiteMax,

I think your mileage is about right. I get about 113 miles when the needle hits3/4. And that's in cold weather. Keep in mind that you have an auto and depending on where you live the cold weather will cause the engine to naturally run rich...reason: cold air is more dense, therefore more fuel is injected to compensate for the increase in air volume.

Regarding your Alpha A/F %...ideally this should be at or above 100% for both banks. Mine were at 95% before the MAF replacement and now at 105%.

Keep us posted on the full tank mileage.

 

The cost on the reprogram was $83 and it took about 45min-1hr. It may be cheaper at your local dealership. Also, they were able to tell me immediately that it was running rich. I guess it takes less time to diagnose everything than it does to correct the problem. Hope this helps.

 

Air intakes might have effects on the fuel economy as well.

I just discovered that the Injen CAI actually decreases fuel economy for those of you have it out there, because the filter is placed behind the radiator fan. However, I did a little experiment by removing the second part (or tube) of the Injen CAI. Then just put the cone filter right after the MAF sensor. Although the temperature sensor is connected to the second part of the intake, just leave it out and tape it to the battery wires so it wont be hanging loose. So now the cone filter is on the left side of the battery and a little bit above the radiator fan. I drove it, it had better mpg and more power than the original set up by Injen.

 

I have the stock intake

 

I went in for a "diagnosis" today at the dealership (even though no codes were being thrown), and I must say that I was treated wonderfully. The tech let me stay out with him for almost an hour as he looked up all the possible causes for excessive fuel consumption and ran some stuff through the consult II. I brought up ideas that the thermostat and o2 sensors may be the cause, so he checked both and they were fine. He kept running other things that were suggested causes of bad mpg and he even gave me the printouts from the consult! So the short of it is that pretty much my engine was running a bit rich, and I had a caliper that was dragging. I replaced the pad and caliper on the dragging side, and the pad on the other($300 installed), and had the ecu reprogramed *with* a 2º timing advance!($40, where whtmax paid $83 - major difference in dealerships .. yea) so I'll let you know how the gas mileage is after I've lost my lead foot from the new timing lol, and I'd also like to share the printouts from the consult for anyone interested or anyone who (if the reprogramming didn't fix my gas mileage problem) can diagnose my problem from the printouts .. well, here:


The second printout (the one that looks like a full page,) as I understood it was before the reprogram, and the other was after the reprogram (still running on 87 octane, which, of course, is now 92 octanne)

 

wow u get 25 mpg? i get like 21 i think.
so 220/half tank, round to 400/tank = 400/16 (around) = 25
anyone else gets it that high?

ok, not only me getting this mileage. i feel bad for the guy getting around 260.
note: i use premium gas, not plus.

 

So they reprogrammed your A/F/ from 98% to 103% and charged you for it.. Theoratically it would have automatically adjusted itself from a rich to lean condition anyways since the drag was fixed???
BTW to an earlier post.I know his problem was fixed by the reprogram...But spraying that into the TB could defiently cause a 02 problem and not trip a code...(Switching from .1 to .95 every 150 milliseconds instead of .01 to .95 causing the A/F ratio to run rich but still not throw a code)

 

no, I paid $40 for a diagnosis of the problem, so technically they told me a caliper was dragging for $40 and then charged me to replace it and just reprogammed everything for free.

Either way, the tech charged me for less time than he spent on my car and didn't try to pull any $hit, so I'm completely happy with the dealership and I don't feel overcharged or like something was stolen from me lol.

 

in the colder months i believe gas is also oxygentated. I forget exactly which months it is. correct me if i'm wrong...

 

When i used a K&N cone filter my mileage decreased as well...after i put the stock airbox back in my fuel economy went back up.

 

Guys, I think your mileages are being miscalculated. Doesn't the 2000 Max have an 18.5 gallon tank, not a 16? Window sticker claims 20 mpg city / 28 mpg highway for an automatic, so we should be getting 370 city and 518 highway miles per tank.

Anyway... I seem to be having a mileage problem too...

Before my CEL came on around 52k miles telling me to replace my ignition coils, I was getting 18mpg city and ??? highway since I don't drive enough highway to make a difference. That's about 333 to the tank. After the CEL came on I started getting about 16mpg, which is just under 300 to the tank. I do have my A/C on 99% of the time that I drive (South Florida - hot hot hot!!!), though... so that could be contributing.

I just replaced ignition coils, spark plugs (used NGK coppers), air filter was replaced a few months ago, tires are inflated to 38psi, used STP fuel injector cleaner last fillup, and I just started using Mobil 1 SS 10w30.

I don't have any performance mods.

What else can I try? I drive almost exclusively in the city... though granted, I do tend to accelerate and brake hard... but I don't think that should have such a big affect on my mileage. I also read that Overdrive saves gas on the highway but wastes it in the city and is not good for your engine, so I've been driving with O/D off for the past few days. I'm just a tad under 3/4 of a tank right now and I have about 65 miles... x 4 = 260. Garbage!

What else can I try?

 

Some food for thought. EPA ratings are overstated. I'm not going to go into detail but do some research on it. The tests they use to measure MPG is not very accurate.

 

Should I replace my MAF? I have read about others getting slightly better fuel economy after replacing the MAF, but I haven't seen any threads on figuring out whether or not mine needs to be replaced.

I did read something about RPM and response from the vehicle, so maybe this could help you diagnose. It said that a totally bad MAF won't let you exceed 3000 RPM, but that's not the case with me; however, I do notice a slight delay in response at times when I drive... like, if I'm going 30-40mph and I floor it, it'll be about 1-2 seconds before the acceleration kicks in and I can feel the pressure of the car speeding up. Sometimes I'll floor it and the speed will just gradually increase until I ease off the accelerator.

What could cause my MAF to go bad? Should I just go ahead and replace it even if I cannot be sure it's bad? Is it one of those guaranteed-maintenance-necessary things on a 2k Max like the ignition coils?

Thanks.

 

Mike, you may be suffering from number of things: delay in shift could be the tranny slipping or your TCM not shifting fast enough, as for bad mpg, what is the mileage on your car, you could have a clogged fuel filter, problem with injectors, your pre-cats could be going bad, MAF is to consider too, etc...

First thing I would do is reset the ECM, i.e. disconnect the battery over night and see what mileage you get after that... 18 mpg is low, but if you are driving 100% in city that may be a realistic consumption... Take it out on a hwy ride 200-300 miles no AC, cruising at 60-70 mph, and you should get mid-high 20's...

 

I'll do a search and see what I come up with. If you happen to have any links handy, I'd appreciate it.

Car has 53k - bought it new. It's a 2000, and I'm told that a 2000's fuel filter is next to impossible to reach. I do use STP Fuel Injector cleaner every 3,000 miles, though - don't know if that has anything to do with it.

By ECM do you mean ECU? I did disconnect the negative battery terminal for about 6 hours while I was replacing my ignition coils (coils: 1 hr, removing and replacing the screw I broke while securing the last coil: 5 hrs ). I've gone through 1/4 of a tank already so when I get to 1/2 I'll fill up and see what my mileage was. Haven't been on the highway yet and I'll make it a point to stay . I'd be happy with 18mpg city (seeing as how Nissan's claim is 20mpg), but being down to 16mpg lately is just nonsense.

 

what to do to checkservice engine light how to get rid of it?

 

two or more when you come a shore i can burn you with my hooked up turbochargded and turbo equipped

 

i can top out 60 mphs in 1.9 seconds

 

There are TSBs for both MAF and tranny. You can look them up in stickies...

Like I mentioned, try taking it out on a hwy, or next time you have a weekend trip and see what mpg you get then... Making short city trips will destroy your mpg any way you slice it

 

I live in South Florida so it's normally a blazing inferno. The mileage started to suck when my check engine light came on, and that was sometime in late October I believe. Temp was still over 80 degrees daily back then. Heck, up until about two weeks ago, we didn't have any days under 70.

Coldest it's been has been about 50 and it always warms up in the afternoon.

Coils were bad and threw a code. I replaced them and the check engine light is gone now. I replaced the spark plugs too. Only thing left on your list is the MAF but I'd like to know if there's any way to confirm that it is bad (or will eventually be guaranteed to go bad and thus benefit from an early replacement) before I go out and spend ~$100 and pay the stealership to reprogram my ECU.

 

You won't likely need to reprogram your ECU after MAF replacement. I have not done it and still runs fine and so did many other orgers. I don't really know of any good way of verifying it... Perhaps someone else can shed some light on it...

What was your mpg before the coil replacement?

 

Before my first ever check engine light: 18mpg city.

After CEL: 16mpg... give or take .25 mpg.

After replacing coils, turning off O/D for city driving, and switching to Mobil 1 SS: Unknown - in process now.

So far, however, it looks like I'm at about 70 miles 1/4 way through... giving me 280 to the tank. That's less than 16mpg... i.e. suckage.

 

18 mpg 100% city sounds about right...

Before you go any further troubleshooting, I think you need to do more exact measuring of your consumption. Another thing is O/D, it will prevent the car from going into O/D meaning you will be running at higher RPM -> higher consumption -> lower mpg. In order to properly assess your situation, you should keep the number of variables to minimum (O/D mentioned). First, as I mentioned, do the mpg calculations properly: reset your trip odo next time you fill the full tank and on the fill up after that take note how many miles you have passed between fill ups (try to make it a full tank). That will give you exact mpg. Looking at the gauge needle is not exactly the most accurate way of doing it...

 

I thought that using O/D in city where you will be stop & go'ing and driving at low speeds will reduce mileage as opposed to improve it because the car will be doing a lot of unnecessary shifting into higher gears, etc... If that's not the case I'll leave it on from now on... sucks too because I felt I was getting a better response with it off.

I plan to.. just mentioning where I am after 1/4 of a mile. Being off by even 5 miles would make a difference of 1 MPG so it is significant.