So I read through the number of gas mileage threads, and obviously many factors go into this. I was able to accept that between this and my STI (horrible two car choices considering I drive to work), i will not have good gas mileage.

My 350z details:

2007
152k miles
BERK Resonated Test Pipes (Currently throwing CEL for Cat efficiency)
Megan Y Pipe
AAM Competition Single Exit Catback
Stock intakes and everything else
V1 Track Wheels with Bridgestone Potenza RE11 245/40/R18 Tires all around (Square tire setup, 18x8 F 18x8.5R Wheel setup)
Previous owner did a clutch and I believe lightweight flywheel cause it chatters like a MF'er

So the flywheel I'm not a fan of, car is a pain at low speeds and does require throttle to get it going. The clutch pedal is also super heavy, but I've dealt with that.

Even factoring in the LW FW impacting gas mileage, potentially the RE11 tires, I've been getting horrible mileage. I fill up with Costco 93 from gas light for about $47 from gas light at $3.09 a gallon so about 15 gallons and this is usually the case. I'm getting a mixed city/highway/highway traffic gas tank of 140-150 miles by the time the light comes on.

Other factors to note, the gas gauge was reading incorrectly until I took out both pumps and cleaned the electric board where the float attaches to with a Q tip and electric parts cleaner. I also had to replace the fuel pump cover O ring for the passenger side but was able to reuse the driver side one. Filling up the car goes to just a smidge under the F line so it doesn't go above it. Not sure if its due to an EVAP line on fill up that stops the pump from continuing or if its gas gauge error even though I cleaned it.

Any thoughts here? I wanted to include all the factors, but I don't see 140-150 miles a tank as sufficient. I know the DTE reading is not really accurate but it depicts 350 miles when I fill up and I'm nowhere close. Even if I try baby footing it a whole tank it doesn't really help.

 

You have something wrong with the car or you are driving too aggressively ... 150miles / 15 gallons is 10mpg.

I would fix the O2 sensor problem first.

 

I mean thats a direct result of the test pipes, they're new OE Denso O2 post cat sensors. Precat Sensor 1s and throwing no CEL.

 

Berk claims no CEL in like 98% of RTP installs.You sure those are the cause?

 

I have berk test pipes with the cel fix, and it doesnt throw a check engine light.

 

Is that really the case? I've heard of plenty of claims that it doesn't work. I mean note, the car is an HR which if rumors serve correct alot have mentioned on here that it is more sensitive to codes versus the DE/Revup. I'm pretty sure these need the 90 degree elbow ontop of the CEL fix thats welded in there or some steel wool perhaps. Also CEL was direct result of post install from test pipes after catalyst efficiency monitors cycled ready.

@achampagne - what year 350z?

 

do you granny shift or drive like fast and furious?

that seem excessivly low, my car averages 19.2 mpg with a 7 liter v8

 

 

Honestly I would not have made another one of these threads, but mine seems excessively low so thanks again for all the input!

I can granny shift (though i really should be double clutching) the car the entire gas tank keeping it away from the upper 3000 RPMs with minimal difference.

It's always mix, but city/highway/low speed top go highway. I would say an even 33% of each type of driving across the board in one tank. Also I ALWAYS reset the trip and MPG counter. I reset trip and MPG after fill up, finish the tank, fill up again and divide trip by gallons needed to fill to determine MPG per fill up. It's always around 10-12 in calculations when the car reads 14.5-16 MPG on the counter.

For my current tank my trip is at 132 miles currently, the gas gauge is just under a quarter at the moment. The first 50 miles of this was pretty much all highway no traffic as it was the weekend. It just tanks downhill. No smell of fumes or leaks, aside from smells generated by not having cats. I was thinking my gauge is inaccurate, but that can't be if each fill up is 15 gallons. I know the fill is under the F line but that would only account for what, 30 miles?

 

ever clean the injectors?

 

This I have not done. To be honest I bought her 140k and have had it for almost 2 years now at 157k miles and its been pretty consistent bad mileage. Aside from the CSC failure (which thankfully had an open recall so i towed it to them to do until i decide i wanna redo the clutch and delete the CSC), the car has ran without a single hiccup. I might try injector cleaner to see what results I can yield. Was just curious if anyone with a LW flywheel experienced anything similar.

 

I honestly don't know if its true about the Berk RTPs or not but that's what they advertise. Is the engine doing anything differently - In other words does it struggle to hit 5k or dog really bad when you are at low rpm? Any chance your plugs need to be replaced?

Do you have a wideband installed by chance..?

 

 

Not sure if the octane would make much of a difference but I have a 2006 and I use the mid grade I get good performance and mileage about 350-375 on a full tank getting even better mileage since I installed HFC'S I know the hotter the fuel burns the faster it's consumed just a thought no physics experience here but maybe worth a try!!

 

Hey, long shot but did the old owner by any chance, changed injectors or the fuel line pressure?
Best way to know if the car is running rich is a wide band O2 sensor (and gauge), that is for sure.

Once you clear the rich / lean factor, then I will suggest you go for the current mods in the car.

My 2 cents.
Al.

 

This bad?

 

I have a ****** chat screen shot of me romping on the vette where it shows me getting 4mpg