Terrible Fuel Economy

[Phatboy]

Hi guys, on my R34 GTR I get 280kms per 50L on BP98. I read the O2 sensor thread and the bad fuel economy thread already, but couldn't find the answers I was looking for.

I drive the car pretty conservatively, so this is quite confusing.

Mods include: GT2860-5s, PWR 700cc injectors, powerFC+boost controller, pod filters, cam gears, dump/split pipe, hipower catback, etc.

The turbo and bigger injectors only went in a month ago. The fuel economy (or lack of) existed before the bigger injectors went in though, so it's not them. I also keep the engine well lubed with 300V filled to the line. The cars only done about 55000 kms.

Is there any easy way of finding out whether the O2 sensor is the culprit? Surely the tuner would have picked it up while tuning AFRs for the new turbo/injectors. Also, does the 34 GTR have 2 O2 sensors? Would these be on the dump pipes? Would this be affected if the dump pipes are obviously aftermarket now?

Dunno if it's related but the boost readout on the stock MFD occasionally shows 0 boost no matter how I drive, despite no change in the boost readout on the PFC hand controller. Guess it's a boost sensor thing.

Thanks very much.

[blind_elk]

If it's mainly city driving, I would doubt the O2 sensors have much input into your fuel economy, since you would have very few situations where you are on constant load / throttle.

If you want to confirm O2 sensor problems, try going for a cruise - repeat CRUISE - up the highway to Albury - if you still have crap economy, then the O2 sensors may be faulty.

Your tuner wil be tuning AFRs for high load situations, not cruise.

If the sensors are not mounted on the upper side of the dump pipes, then they will poop themselves quite quickly (so I believe).

[SLY-25T]

ive heard that u can tell if they're stuffed by pulling them out and shaking them next to ur ear. if u can hear a little rattle then its stuffed.

not sure if its true just throwing it out there.

[(OO)SKYLINE(OO)]

I would get your mechanic to diagnostics test to see if the O2 sensors are cycling.

GTR's have two O2 sensors, if both are cycling (as in, you will se a graph with a line cycling up and down on the diagnostics computer) then they are fine.

If ones out then change it. O2 sensors cost about $100 each + your mechanics labor, what ever they charge.

As you know O2 sensors are there to make sure the car is not running too rich or too lean...

Other then that, I check your fuel injectors, but I assume they are NOT leaking as you have just put new 700cc ones in... Check them anyway...

Run your fuel tank low, put a bottle of injector cleaner in then fuel it up (BP Ultimate - my suggestion).

Clean your air pods and get your mechanic to check your Air Flow Metres out.

see how your go, as these are just the basics...

[MrStabby]

Get someone with CONSULT to take a look. Failing sensors are sticky to zero - ie they will jump off with a bit of encouragement (throttle). Dead sensors read zero.

[Phatboy]

Oh ok.. looks like I will get my mechanic to take a look. Thanks mates.

[NewKleer]

Get someone with CONSULT to take a look. Failing sensors are sticky to zero - ie they will jump off with a bit of encouragement (throttle). Dead sensors read zero.

or 0.3v, which is volage sensors will often start at when cold. (but give it a couple minutes for the heater to warm it up)