N/a Fuel Economy Thread

[jrm]

I'm a bit stunned by N/A owners only getting 320km out of a 'tank' (whatever that is in L - i'd be curious to hear how many they're putting in).

I keep an eye on my trip meter and reset it everytime I fill the car to the brim. I almost always go to the same petrol station & bowser. I generally get about 330-350km out of 50L (when the light first comes on in the 65L R34 tank) - and that's driving like nut hammering it at every set of lights - with a turbo. On the highway it'll get about 550km (or more) out of 50L (it's been different between runs, depends on the highway, how many hills, how bad traffic is). I don't consider the fuel economy too bad to be honest...

[KezR33]

My Supra gets around 500-550km per tank, which is quite a bit better than my NA R33 Skyline (400-450).

Probably due to it having a bigger tank though, I don't actually know their sizes.

Edit: Supra: 70L - Skyline: 65L.

[Turk1]

My tank is 50L. It is currently sitting on 325km, the light hasn't come up yet so i might be able to hit about 340km this tank. I am basically averaging 15L/100km...it just can't be right. My idle gets a little bouncy after the car is warm, that could have something to do with it.

[SKiT_R31]

There is obviously somthing wrong with your cars, I've had an N/A before and it had beautiful economy (10-11L/100 city) i had a turbo one and it was exactly the same (stock). I now have an R33 GTS4, and its not quite as good, about the same as what others are getting (12-15L/100 pending driving style) and i know its not right, i can smell fuel at idle, plugs are black. Car drives perfectly though.

I think some of you need to do a diagnostics check with your ecu's, make sure all the sensors are right and happy (especially the O2 sensor). Replace the fuel filter, contact clean the AFM, check for fuel leaks (out the filler cap, along the fuel lines, you'd be suprised).

I'm doing a full service on my GTS4 this weekend, and will be suprised if i cant get it down to a happy steady <11-12L/100 (it wont be as good as my other cars since it is a 4 door 4WD, i.e. more weight). I've got a new genuine O2 sensor, some electric contact cleaner (non residue) - the car has an oiled K & N pod, i'm going to fit a paper APEXi (non oiled), some thinner 100% synthetic oil (its got like 20-50 in it atm :|) new filters, etc. Ontop of this i will do a diagnostics check, retention belts and check pulley's for resistance, and replace all my fuel lines (as they are all cracked and on the edge of leaking, if not already). As for plugs, it supposidly has iridiums in it, i'm going to check these, clean and gap (i cant remember if they were 5's or 6's) if they are 6's i will fit 5's (and keep the 6's for when its boosted), as people would be suprised the difference a plug temp range makes to efficiency.

On top of this, i've tested the timing and noted it is 30 degree's advanced, im concerned it might be R & R'ing (though its perfectly smooth and i've heard no detonation) i'll wind it back to ~ 20 and see how it goes.

I am interested in peoples results with the splitfires, as this car has them fitted, i cant really see how coilpacks could be detrimental to economy, but if im still having economy issues, i have a new set of genuines i can fit. Perhaps the issue with them is just from O2 sensors being faulty from unburnt fuel after the previous coilpacks died?

And if all that fails, it has to be an issue with injectors, remember they are quite old, and normal wear will make them flow too much. I have some new 25det injectors, which i will fit when i turbo this car, so if its just injectors, ill live with the economy until then (when ill PFC it as well and economy tune it for some tame power - as this is my daily).

So yeah, might be some things their for people to try, oh and i run ALL my cars on E10 98ron, from my high comp high powered N/A, my 30DET silvia, my 30E+T R31, 7MGE+T cressy, subaru's etc, it is a beautiful fuel, clean (open up an engine that uses it, its silver metal, not carbon black), great knock resistance (better than normal 98ron imo). Cars love it, and economy doesnt change for the negative, i find i get a touch better city, and a touch worse hwy (because lambda O2 sensors) but it all evens out for the posetive (since its about 20c per litre cheaper).

Off topic, but does anyone know if there is anything different with the 4WD ECU's compared to a normal 25de/t ecu?

sorry for the essay...

Edited August 25, 2009 by SKiT_R31

[Turk1]

The essay is all good bro. Gives everyone an idea of what to look for, I've been suspecting it might be the AFM. If it ain't that then I will knock down all the other things that it could result into.

[FULOCK]

There is obviously somthing wrong with your cars, I've had an N/A before and it had beautiful economy.......

Ok, now im starting to really like this thread as we might be getting somewhere now.... and not just figures being thrown all over the place...

Could anyone who had bad economy at first, Post up what they did/tried (eg. the suggestions posted above by SKiT_R31) on their RB25DE or DET which greatly improved their city/traffic economy!

SKiT_R31 - love your work - I like the essay too!!

If we can get members to list what they did/tired on this thread, and it worked for their car to improve economy, this thread will be GOLD imo!! It will give everyone a clear understanding and a list of troubleshooting procedures they can go through on their own car if their fuel economy isn't as it should be.....

[Turk1]

Well I think I might of done my best tank yet haha. I was sitting on 350km, the needle was on empty but with the light hadn't come up yet, so maybe I was on the verge of hitting 360km....maybe 370km. Refilled yesterday, so this whole tank I will sit off the acceltor and keep it below 3k rpm. See how it all goes.

[666DAN]

Well everytime I'd see a big dip in economy (we're talking dropping down to about 280kms/50L) I'd run the R34 O2 sensor diagnostic and bingo always come up with a slow responding sensor. I've changed the sensor in my car 3 times in the past 4 years.

It's a pretty good diagnostic function as the AFR is meant to cycle so many times in a 10 second space at a few thousand rpm.

[FULOCK]

Well everytime I'd see a big dip in economy (we're talking dropping down to about 280kms/50L) I'd run the R34 O2 sensor diagnostic and bingo always come up with a slow responding sensor. I've changed the sensor in my car 3 times in the past 4 years.

It's a pretty good diagnostic function as the AFR is meant to cycle so many times in a 10 second space at a few thousand rpm.

very interesting.... for anyone like myself that has never done one of these diagnostic tests..... how do you do one...??

is there a thread on it somewhere here????

[666DAN]

Hmm I can't find the file, basically you run the normal ECU diagnostic (short the pins on the consult plug with a paperclip with the key turned to Acc, then stop shorting to enter diagnosis) then start the engine. Rev to 2000rpm and hold then count at least 5 flashes of the check engine light (rich/lean cycles) over 10 seconds.

[central coast person]

i had bad fuel economy, i was getting like 300km to my 65L tank....then i built a new engine and im getting 450km around 80km zones and less (central coast driving). On the highway to Newcastle i put like $20 in (i use Vortex as my fuel) and it took me there and back so im getting about 600km to the tank on the highway.

I guess you will have to write a list of everything you change when you build a new engine because there are many possibilities, my GTS-4 is a 1995 model so its 14 years old and my injectors were pretty clean but the plastic clips on them were starting to decompose..........good luck finding the faults.

[MissR34]

hey guys my R34 had shocking fuel economy 400kms out of a tank...........then i put in a new intake piping, and discovered that my stock airbox (the resisnator bit) was melted underneath!!!!!! now that ive got the new intake piping my fuel economy has gotten better.......and with a finished tune ill get even better....so ill have to let u all know how she goes

[Turk1]

Got 430km in mine the other day, had a bit more in her aswell so things do look like there getting better haha

[HairyMerkin]

I get around 320kms to the tank, R34-gt25. I'm going to test the o2 sensor, otherwise I have no idea.

[TwoCents]

Got 400km on the start of the last bar on the fuel gauge... then filled up, that highways city driving and abit of thrashing. Still had quite abit left in it

[dori34]

previously on the NA it use to get around 450-480 and over 550+ on freeways

r34 rb25de Neo

5spd

catback 3" exhaust

98 octane (mobil 8000, vortex 98, optimax)

[DELLER]

I run 95 octane and i get around 350-390, thats driving around town,

only mods are pod filter and a cat back extaust,

Just getting over 300 man thats not alot

[peterw]

I'm getting 10.5L/100km consistently at the moment, with a catback and a high-flow panel that could do with a replacing

[HairyMerkin]

With the air con off, and really grandma driving (keeping it 3k RPM and below) I get 400kms.

[Crackfox]

Does having a turbo make any difference to economy? I have gotten 550kms to a tank in normal around town conditions and 650kms highway cruising at ~95kmph, couldve pushed it to past 700kms as well but wasnt game to try it. I usually get around 460-470kms per 50L around town. This is in an r33 gtst and seems to be better than most of the N/A figures here.