I'm getting about 170 to 180 miles per tank, I don't beat the car and I only drive 15 miles per day to work, 7 each way.
03, Coupe, 114K, Borla true duel exhaust, Z1 high flow intake, spacer, Cobb stage 2+ tune with a perfect 14.7 AFR. The Cobb tune wasn't my choice!
No faults, MAF is clean, just installed the intake, but my old ARC filter wasn't horribly dirty. Throttle body was replaced and looks clean. The car drivers smooth and pulls hard, no misfires or hesitation.
Just replaced the spark plugs to one step colder, the old ones didn't look that bad at all. They were not fouled out at all. I do smell raw gas coming out the exhaust on start up.
I haven't had the chance to remove any 02 sensors to check condition and I don't have an advanced diag tool to watch 02 signals yet.
Saving for an Z1 UpRev tune. I threw in a can of Royal Purple Max Clean with my last fill up, I only run 91.
Any ideas? I know it'll be just a guess, this is all the info I have to work with myself. Maybe it's the tune? Oil doesn't smell like gas and I don't smell gas leaking anywhere.
I did see an old thread were the someone ran seafoam through the intake, I'm wondering if I should do the same. Any thoughts are welcomed, thanks

 

Question, if the old plugs looked like they were burning fine why did you switch to one step colder? You'll likely just end up with a set of fouled plugs due to the heat range being insufficient to properly clean.

As for the mileage question though, you didn't actually say how many mpg you're getting. EXACTLY how many mpg is the car getting.

 

20 gallon tank getting 180 miles per tank would be around 8 miles per gallon, right?
As far as replacing the plugs Z1 Motorsports recommends one step colder for modded cars�

 

I've never seen an NA VQ35DE that needed colder plugs but just keep an eye on them after 10k miles if the ceramic white insulator part in the middle looks black then go back up 1 heat range. If not then keep running them.

As for the mileage yeah that's pretty awful, "normal" city driving the worst I get is about 13mpg and that's a lot of stop/go traffic. However if I'm heavy on the throttle a lot I have DEFINITELY been down into single digit mpg, 8mpg is about the worst I've ever gotten though and it was a very short drive with a highway onramp so I was basically full throttle on the onramp then back off the highway into a short stop/go lights for a few blocks.

Track your actual mpg for a tank or two though, chances are you didn't actually use a full 20 gallons (you would be completely empty) across 180 miles.

Fill up, reset odometer, drive until you're down to 1/2 tank, fill up and find out exactly how many gallons you went across an exact distance.

Do you know if you have an ECM that can be Uprev tuned? I think it should since it's a coupe and I don't think they came with the early 2003 ECM that was untunable.

 

Your absolutely right, I never let it go to full empty. So, it�s probably not that bad. But, I will try what you said.
And as far as the plugs, your right I usually see one step colder on boosted engines, but I�d like to think Z1 knows what there talking about.
I sure hope my ECU is tuneable that would blow.
Thanks for your reply bud

 

I'm on my third Infiniti since December 2005 and on every one of them I got poor MPG on short trips local driving and excellent MPG on long trips from NJ To Florida many times exceeding 27MPG on a single tank of gas of over 300 miles. I have never used anything other than 87 octane in the over quarter million miles that I have driven on my three Infiniti's



You can see the results of the short trips while in Florida compared to the results on I95
I would suggest that you fill up your tank,, drive 300 miles without stopping, fill up again and divide the gallons to fill up into the total miles traveled.
I'm sure you will be surprised at the result.

 

If he is getting poor mileage, the surprise is going to be when the engine sputters and dies because it's out of gas. That's 15 MPG on a 20 gallon tank, and he's not even close to that....

 

Haha that�s funny. Yeah no way I�m going 300 miles without stopping.

 

It's easy to see if your ECM can be tuned, just remove the glove box to get a better look at the plug.