Gizm0

iTrader: (1)

Everything is in the title. Does anyone know how our car's MPG computer calculates the gas mileage and dte?

I want to know all the factors that are taken into account by our cars to do the calculation (speed of the car, throttle position, amount of air measured by the MAF etc...)

phatboislim

iTrader: (27)

i trust the DTE over teh MPG...MPG...just do it the old fashion way

Gizm0

iTrader: (1)

Well, the reason why I am asking is because I have been getting pretty ****ty gas mileage lately (18-20mpg mixed driving rather than my usual 25mpg average) both indicated by the trip computer, and calculated at the pump.

I suspect that my MAF may be going bad, or maybe my throttle body (which I cleaned recently and every since i did this, my gas mileage went down drastically...)

phatboislim

iTrader: (27)

and you're not throwing codes?

Gizm0

iTrader: (1)

No codes... but mileage went down... performance is still very good, but sometimes it goes down...

tonyinclearwater

I was wondering this as well. I just purchased a 2003 TE AT.

I drive like OLD OLD grandma.

My MPG is showing 22.3 or so after mostly in town driving, and after a weekend of going to a LOT of garage sales. The garage sale driving naturally involves lots of stopping, restarting, and low MPH driving through neighborhoods.

So, anyway, back to the topic at hand.

The DTE. Does the car somehow KNOW how much gas is in the tank at any given time?

I am about 1/2 full right now. If I go and put a gallon in, will the DTE increase by however MPG it says I am getting?

If I siphon out a gallon, will the DTE actually immediately go DOWN by some amount close to my MPG?

For the MPG, does the car measure the amount of fuel delivered through the injectors and compare that against the distance traveled?

I hope someone who knows this for sure will chime in.

Always an honor to be a contributor to Maxima.org,

Tony

Feldman

iTrader: (1)

Have you checked pending codes? pretty sure knock sensor doesnt cause the light to come on but shows as a pending code when you pull them.

As for how the MPG is measured, i dont know specifically for the maxima but typically the ecu determines the fuel being used by using the load and duration information from the injectors, from there its simple math.

Determing the miles until empty is not exactly accurate unless you are standing still on a flat surface. The level sensor sends a variable voltage to the ecu depending on the fuel level that corresponds with a fuel level (gallons remaining) then multiplies that to your average MPG and tada miles until empty

Gizm0

iTrader: (1)

How do I check pending codes?

I have a replacement KS that I bought a couple of weeks ago. I need to install it, but I've been procrastinating...

However, I'm pretty sure it comes from the fact that I cleaned my throttle body. I cleaned my TB about a month ago, and every since then, my gas mileage went down. Not sure how that could be related though...

tcb_02_max

iTrader: (5)

Relating to how the MPG is calculated, does anyone have an [always] extremely "optimistic" calculated mileage? Mine consistently reads 10-20% better than I actually get (i.e. hand-calculated)... e.g. reads "34.0" when I actually get 28.7 mpg. Any way to "retrain" or reset this, or am I stuck with what I've got?

Child_uv_KoRn

iTrader: (7)

If power is good, but mpg sucks that's pretty much a sure sign of a dirty/bad maf.

But remember there's 101 things a crap maf can do besides that haha.

Waxima

iTrader: (3)

My car doesn't even calculate the MPG... the gas light doesn't work either. This is probably a good thing because it forces me to not be lazy and do the correct mathematical calculations for the MPG as everyone should. I would never rely on the computer to put out an accurate number.

OP, I have the same problem as you. I get 19-21 mpg (21 if I'm lucky) doing 80% highway driving. No CEL but I went to the shop after the engine shut down in traffic about 2 months ago and he said that the car threw codes for the MAF. I'd do the hard calculations for the next few fill-ups (and USE PREMIUM if you don't already) and see what your actual numbers are and if there are any trends to them.

Gizm0

iTrader: (1)

I always use 93 octane. The 19-21mpg I get is when dividing the miles by the gallons filled up in the tank. The trip computer tells me +/- 24/25mpg...

Question, will the autozone code reader be able to catch anything if I don't have a CEL? If not, i'll use a voltmeter to check my MAF and if I need a new one, I'll go for a 2k1 MAF and hope my gas mileage will get back to normal.

trooplewis

iTrader: (1)

Yours is normal.

Both my current Max and my previous Altima overstated mileage by 10-15%.

If it said I was getting 30mph on the car computer, when I filled it up I actually got 25-27mpg. I don't know whay they make the computer so optimistic, I'd rather it was realistic.