Fuel Economy

[justin911]

ok peoples...

this bad fuel economy is getting anoying again... had it for a while now.. 250km if im lucky

I can drive on the highway or in the city for the same amount of time and ill still get in the 200's

- the o2 sensor is fine i believe, it reports readings between 0-1v according to the pfc.

- the afrs have been checked on a dyno and are aparantly fine..

- never any black smoke or anything

- i've changed fuel filter a few times.

- tried that injector cleaner you get from the petrol station a few times.

- the afm seems fine i dont realy have any wierd idle or missing or anything problems..

- got new tyres recently so it cant be that anymore

- changed all the other stuff, spark plugs etc during servicing..

- driven up and down the road a few times trying to see if petrol was dripping out anywhere.. so doesnt

seem to be leaking..

- doesnt seem slow or wierd or anything

- the engine was rebuilt 500km ago with stock internals but i dunno if that would make the econemy slightly better ?

also because it was recently rebuilt im driving slower so if anything i should be getting better fuel eco now, but grr im not

oh yeah the closed loop thing on the pfc is enabled and when im cruising round at like 60km the inj duty cycle is like 4-7% which isnt to bad ya ???

anyone got any other ideas on what to check ??

thanks

[12DFY]

Check your catalytic converter mate, having 33 with same sort of prob and replaced cat converter and it seems to have improved economy somewhat

[justin911]

ive got a hi flow one i think.. its an xforce 3" one from there kit.

[justin911]

come on ppls time is money

[benl1981]

Seems like youve covered all bases.

On the dyno when in closed loop were the AFRs at 14.7 or very close to that?

Did you blow your motor? I tought you just got your PFC tuned a few months back?

At around 60km/h I think my inj duty is at about 4% in 4th gear..probably about 5% at 70km/h so can't see a problem with those figures.

Strange..

Even on the base map of PFC (Usually very rich) I could still easily get 400km to the tank going in some traffic etc (i.e. about 11-13L/100km) which seems to be a fair bi better than yours..

Hope you find the culprit

[justin911]

yeah i had some issues in the timing region so down she went like a $2 whore... shes all perfect again now though

Im not sure on the exact afr's, but the fuel eco stuff was checked on the dyno for like 30 mins or so.. i was standing around but i didnt take notice of the afrs.. i'll get them checked over again though just cause im running out of ideas hehe

ive also ruled out the neighbours syphoning out the petrol..

thanks for ur help

[justin911]

i was searching around again.. and someone fixed there fuel eco problems by changing the coil packs... hmm sounds abit dodgy..?

is it possible coil packs could be doing it ? and if so should i be noticing wierd stuff happening besides the bad fuel eco ?

same with the injectors ???

thanks again ppls

[benl1981]

Gee..the poor rb25, or poor Justin's wallet - what happened to your timing to blow up the motor??..were you tweaking it or just running the as tuned maps. I get a bit of check engine flash but the tuner is convinced it is just mechanical noise as he pulled out about 10 deg of timing at certain spots..

Bit worried because it costs more than $2 to get them back up again, right?!!

I think youd notice coil packs eitheron boostor at idle if they were the culprit.. Have you had a wheel alignement? When you back off does the cars low quite quick (indicating too much toe in for example)?

Could possibly be a leaky injector but you would think that would be noticeable with black smoke on startup or missing?

[justin911]

timing belt area i mean sorry, not the timing on the pfc etc..

[Busky2k]

Whilst driving, check the O2 sensor on Sensor Chk is looping from 0-1V when cruising at 60 or even accelerating off the lights slowly. If its stuck at 0.7V or more whilst on the move, you're running rich.

Have you determined your L/100ks? ie fill up, log the ks, fill up again and see how much petrol you went thru..

[RANDY]

I get 350, as everyone has heard in the 02 sensor thread.

If my tyres are slightly deflated (one of them has a slow leak) i'll get 320 to a 50L fill. Normally I make sure they're all at 42psi... might want to try running that sort of pressure? (i'm on standard rims/tyre)

My wheel alignment is spot on, drives straight as anything and doesn't pull with the grooves in the road.

I'm still hunting for that ever-elusive 400km mark though!

[justin911]

i gave her a test run tonight... was doing 100km/hr @ 3000rpm or so in 5th gear on the freeway and it was mainly cycling between 0.5 and 0.6 volts... guess ill get the ol afr's checked again asap.

thanks for ya help

Whilst driving, check the O2 sensor on Sensor Chk is looping from 0-1V when cruising at 60 or even accelerating off the lights slowly. If its stuck at 0.7V or more whilst on the move, you're running rich.

Have you determined your L/100ks? ie fill up, log the ks, fill up again and see how much petrol you went thru..

[vape]

i dont understand you guys that get so little km's off a tank, i get always over 450 and only ever fill up 55L or there abouts, just until the fuel light comes on.

always used bp ultimate and reset the ecu when i got the car for the first time.

stock series 2 r33 with the turbotech boost controller and a slightly bigger exhaust (have no idea about it - was changed for compliance)

[R33TOM]

vape, you got a fairly stock car so the mileage you get will be very different from some of the other guys on here.

For starters the PFC ecu will make a big change to the mileage depending on how the cars tuned and how much more power its producing.

At the end of the day because pretty much every skyline is modded differently the fuel economy of everyones cars will always be different

[Busky2k]

i gave her a test run tonight... was doing 100km/hr @ 3000rpm or so in 5th gear on the freeway and it was mainly cycling between 0.5 and 0.6 volts... guess ill get the ol afr's checked again asap.

thanks for ya help

If it succesfully dips below 0.3V and goes higher than 0.7V during the cycling, then thats a good thing. It should cycle from 1-3 times per second if the AFR is spot on. if its just sitting at one particular voltage and doesnt move much, then you are either running rich or lean (rich being the most likely cause).

Also take a look at the PowerFC tune thread, they talked about increasing the ignition timing on various points on the map. This may help too.

[benl1981]

Powerfc should improve fuel consumption R33TOM..Most of the time the stock ECU runs very rich. Leaning out AFR is a benefit of the powerfc..A good tune on Powerfc even with lots of mods will = not much more than 12L/100km in most driving I would think. If you start boosting then the big hp boys will be seeing high fuel usage.

Some people say the bigger the tubo the better fuel consumption in conteolled driving as it doesnt come onto boost so easy..

Edited April 5, 2006 by benl1981

[siddr20]

Im not to sure if this will help(helped me).. Anywyas i was gettin about 300 to a tank as well.. I was like WHAT?? but didnt concern me as much, coz i just bought the car back then and hardly drove it..

At the same time i use to get rough idle, went back to complicance shop and got my charcole canister changed..

Now im getting 420 to a tank!!

Maybe try changing charcole canister??

[justin911]

siddr20.. can i just empty the canistor instead of getting a new one ??

im gonna get the afr's checked out a differant place tommorow so hopefully that will provide more info or atleast rule out some stuff

thanks again everyone

[Cooper]

^^^ Im also interested to see how to fix / replace the charcoal canister. I am having a similar problem with my ecconomy and am still trying to figure it out. 250 to 300 Km out of a tank on a stock GTR is not good.

[paulr33]

the charcoal thing is for emissions it wont affect fuel economy