Without changing any driving habits my mileage has really gone south! My Z never did any better MPG than 16.3 to 17.2 according to the onboard computer. Suddenly over the course of the last week, it has dropped to 13 to 15 at best.

The last mod was a Borla TD and Kinetix cats. All was well after that install for about a month. Now mileage is suffering. The car is running fine as usual.

Any ideas?

 

whoaaaaa..... im not sure what kinda style you are driving, but i get 22-26 mpg base on the onboard computer. I also keep track of it by reseting the milage screen everytime i put in gas and its fairly accurate.

 

hmmmm that is odd, my car has 100 miles on it and im averaging 21 mpg

 

Is your gas guage reading properly? Fill it up at the pump and see if the needle is going all the way to F. If not, then take it to Nissan and have them look at it. It could be that your sensor has gone bad.
http://www.nissanhelp.com/Bulletins/350Z/Year.htm

 

I think the computer or sensor it reads may be bad. I watched carefully today and mileage stays relatively constant while cruising but at a stop it is dropping .5 MPG every 30 seconds or so. I know that idling is wastefull, but it never dropped that fast before. In the span of sitting at 1 red light I went down about 2 mpg! Its never gone down that fast at idle in the past.

 

its hot out now too, remember

 

Yo,
that's actually normal. Your computer is adjusting to your new mods. Mine averages 17.5 and it went up to 28mpg then down to 14. It went back to normal after about 400 miles of driving - this was after exhaust and testpipe, as well. did the same thing with the popcharger, although not as severe.

 

Your'e better than me. Since I got the car in Sept '05 I HAVE NOT GOTTEN BETTER THAN 15MPG!!!!!

 

Next time, remember how many gallon you put in the tank, and how many miles does the Z take to empty. The do the math yourself, 400miles/20 gallons = 20mpg. my Z usually run 400 miles/18 gallons = 22.2mpg (if you dont trust gas guage reading)

 

+1...I don't think the guage in the center concole pod is very accurate...it's more for show. You have to constantly reset it so that it takes into acct your average speed. The best way to calculate your MPG is the way tcn stated above. Run the car till your close to E, fill up tank and keep receipt so you know how many gallons it took. Reset trip readout on the odometer and then when you get down close to E. Take the total trip miles and divide by the gallons pumped

 

Release your e-brake.

 

Fuel line leak?

 

I was getting 12mpg when I was doing the 1000 mile oil consumption test (per dealer for excessive oil consumption). It turned out I was burning excessive oil and the dealer changed my short block, under warranty.

Check your oil level too.

 

after installing my Stillen exhaust (along with a Pop) my gas mileage seems to have gone down as well. could the issues be at all related to the A/F ratio? I've been considering getting my ECU reflashed to possibly help the situation (which I've been told doing so might)

 

Could be that they are putting Ethanol(sp ?) in the gas now

 

I have the same problem on my Z after installing the popcharger. However, the gauge is absolutely not accurate in the first place, it fluctuates up and down like a champ the whole time in local driving. Dont trust the gauge, you should just calculate how many miles you have driven before the yellow light goes on to estimate MPG.

 

the mileage computer keeps calculating even while you are standing still. so your mileage gauge will say you are getting horrible gas mileage, while you actually are not. it is a design flaw in my opinion. it should only calculate while the car is moving. it is even worse if you have reset it recently, as it will not have many miles to base the average off of and standing still will drop it quickly.

 

Fuel mileage does not suddenly change.

Going from winter to summer mileage may decrease 1 mile/gallon. The problem is accurate measurement of mileage from one tank to another. If you calculate 17 mpg for one tank then 15 mpg for the next means little: just that your driving pattern is different.

 

so many experts, so little truth...

 

my idea is right though, lol. test it. reset your mileage comp while on the freeway for about a half hour, to get a really high mileage count, then go home and let the car idle in the driveway. your mileage will drop huge amounts, even though the car is not even moving.