r34 GTT Excessive fuel consumption on stock Rb25det neo

[MarcusH]

I bought an r34 gtt sedan maybe about 6 months ago now and its been a daily ever since. Its been a dream and I'm in love with the car but its got a couple off issues my main concern being its fuel consumption , I had previously owned an NA r34 sedan which got about 13.33L to 100kms and when i sold my na for my new turbo 34 which gets 19.50L to 100kms i thought it was a bit heavy but its turbo so what can I expect?  but now after reading a few posts here it seems i should be getting at a minimum of 15L to 100kms out of a tank when im lucky to get 19L per 100km especially considering how stock it is and my fuel consumption is on par with 400kw rb's 

Only mod is a blitz return flow fmic which was installed prior to me purchasing the car and a decat. - Stock op6 , haven't pulled it off so haven't had a chance to see if there's any play or if its been high flowed 

I have replaced/changed all the easy stuff, spark plugs , oil change, fuel filter , new 02 sensor

Not really sure where to go from here.

The people I bought it off told me when they bought it it had a full exhaust system , screamer pipe , the fmic and a pod filter. My theory was that it was tuned and then when I put everything back to stock the ecu didn't know what to do as it would be alot more restrictive? But then I hit 180 and it cut my fuel which then makes me think its never been tuned and is still running the stock map?

Its a stock head to as Ive done the rocker cover gaskets and there was absolutely nothing special there.

Im thinking its either leaking or bad injectors or possibly something to do with the fmic as it could be taking in a lot more air? 

Any suggestions or ideas greatly appreciated 

 On a side note my house mate who has a very similar dead stock 34 GTT’s turbo barely makes any whine or spool noise vs mine is loud as f**k compared.

We put this down to the fact mines auto and his is manual. And when we went to a drag and raced side by side we were both neck and neck no difference in power at all 

Edited April 4 by MarcusH

[Kinkstaah]

You won't know until you know. It's possible whoever had the mods used a different ECU when using them, and put a stock ECU back in.

Have you done something crazy like a full tank of gas doing nothing but cruising along at 100kmh? And I mean nothing? because look at your economy then and you will know if something is out or not.

The mysterious loudness implies there could be a leak, and some of your driving is going into making noise instead of it efficiently giving power to the ground. I don't mean skids, I mean boost leak etc etc etc and/or something else is off.

It is not because it is auto. You can barely even hear the turbo in a genuinely stock R34 GTT at full throttle, even if you actively listening out for it.

[MarcusH]

17 minutes ago, Kinkstaah said:

You won't know until you know. It's possible whoever had the mods used a different ECU when using them, and put a stock ECU back in.

Have you done something crazy like a full tank of gas doing nothing but cruising along at 100kmh? And I mean nothing? because look at your economy then and you will know if something is out or not.

The mysterious loudness implies there could be a leak, and some of your driving is going into making noise instead of it efficiently giving power to the ground. I don't mean skids, I mean boost leak etc etc etc and/or something else is off.

It is not because it is auto. You can barely even hear the turbo in a genuinely stock R34 GTT at full throttle, even if you actively listening out for it.

Im close with the people I bought it off and they reckon the fella they bought it off didn’t touch the ecu or didn’t revert it as it was a financial emergency sale. But as you said wont know till i know. Wonder if a simple tune is needed? If it’s on the stock the stock ecu tho im not sure how the map could have changed. 
 

ye not a bad idea w the leak just not really sure where to start in terms of diagnosing a leak. 
 

Been told by a few that it doesn’t sound like a leak that it sounds natural so I’m gonna hold onto the hope it’s a high flow 😂

 

side note not sure if you’d know or anyone that’s reading this but the fact my fuel cuts when I hit 180kph means that I 100% have a stock ecu right?

[Kinkstaah]

39 minutes ago, MarcusH said:

The people I bought it off told me when they bought it it had a full exhaust system , screamer pipe , the fmic and a pod filter

Been told by a few that it doesn’t sound like a leak that it sounds natural so I’m gonna hold onto the hope it’s a high flow 😂

side note not sure if you’d know or anyone that’s reading this but the fact my fuel cuts when I hit 180kph means that I 100% have a stock ecu right?

Yeah the stock ECU has a fuel cut at 180kmh. Having a car with a screamer without a tune would boggle the mind, but I admit this and "I had to sell it due to emergency financial situations" do somewhat go hand in hand with regards to questionable mod paths.

The cars are 90's cars with not-great-fuel economy to begin with, the often quoted figure is 11-12L/100km, and that'd be with a manual, not a old style torque converter auto which would have added to it.

Now if your N/A one got 13.3/100 then I suspect your foot or commute is heavier than most.

I remember commuting to Sydney I got 600km from a 50L fillup for purely highway driving. The fact you know there is a speedo cut at 180kmh is also a bit of a giveaway that your driving has not exactly been economy focused, plus the previous N/A being involved in a smash.

Correlation doesn't mean causation but...... y'know.

[Dose Pipe Sutututu]

Is that screamer those silly pipes that go on the stock turbo?

If so, I imagine a Venturi effect is present when you're coasting off boost and the narrowband O2 is registering a lean condition. Your ECU is now adding in fuel to compensate for the lean condition.

[GTSBoy]

I concur with much of the above. A few points though.

It could have a Nistune in it and still have the speed cut. You're not forced to disable it!

13L/100km on an NA 25 is terrible. As Greg says, that is a bad sign for your ability to modulate the throttle smoothly. If you apply a lot of transient throttle to a GTT, you could well use that much more juice.

Just because you put a new O2 sensor in does not mean it is working. You need to check that it is working by connecting a Consult capable device and looking for the feedback swinging low-high, as you drive.

Boost leaks will cost you fuel. No arguments.

Suction leaks will NOT. Extra air only means extra fuel if the air passes through the air flow meter. So if you have a vacuum leak that is somehow not also a boost leak, then it is not causing more consumption. But otherwise see the point above.

A highflow will NOT cause excessive fuel consumption unless you spend the whole time on boost. And then it might, because the 9 to 10+ psi section of the maps is excessively rich and retarded to prevent the rich from being retarded.

[morboost]

remove positive battery terminal, hold foot on brake for 60 seconds, refit positive battery terminal, now drive car as you normally do ( do this before your morning commute) , your ecu will go through a relearn phase-  take note of results, better to have a full tank before doing this to track if improvements have been made. 

[GTSBoy]

^^ This is not a solution. If the extra fuel is hiding in the LTFT then it will just come back after the ECU has had a panic and bashed all the extra fuel back into the STFT (and then rolls it back into the LTFT).

[Dose Pipe Sutututu]

I urge OP to take a photo of their dump pipe/screamer

I'm curious to see if my assumptions are correct.

[silviaz]

On 4/4/2024 at 6:25 PM, Kinkstaah said:

Yeah the stock ECU has a fuel cut at 180kmh. Having a car with a screamer without a tune would boggle the mind, but I admit this and "I had to sell it due to emergency financial situations" do somewhat go hand in hand with regards to questionable mod paths.

The cars are 90's cars with not-great-fuel economy to begin with, the often quoted figure is 11-12L/100km, and that'd be with a manual, not a old style torque converter auto which would have added to it.

Now if your N/A one got 13.3/100 then I suspect your foot or commute is heavier than most.

I remember commuting to Sydney I got 600km from a 50L fillup for purely highway driving. The fact you know there is a speedo cut at 180kmh is also a bit of a giveaway that your driving has not exactly been economy focused, plus the previous N/A being involved in a smash.

Correlation doesn't mean causation but...... y'know.

600km?! That's amazing lol, was that turbo or non turbo? I'd be lucky to get 400km on a tank lol (though that's mods for you i guess lol)

[GTSBoy]

51 minutes ago, silviaz said:

600km?! That's amazing lol, was that turbo or non turbo? I'd be lucky to get 400km on a tank lol (though that's mods for you i guess lol)

I think you misunderstand. This was Greg driving from Melb to Syd (or return) at a constant 100km/h on the highway. Very little throttle movement, very little accel/decel. You should be able to get 8.5 l/100km under those circumstances (which is effectively what he reports - 50L for 600km is 8.3 l/100km).

I drive my car to & from work every day, in traffic, on a mixture of 50, 60, 90 km/h roads (and therefore at up to 110km/h!!) with traffic lights and freeway sections. 28 km each way, so about a 30-40 minute drive depending on day, direction and traffic (which is enough for the majority of the drive to be "fully warmed up". I typically get flat 10 l/100km every single week. OK, maybe 10-10.5, every single tank of fuel. RB25DET Neo.

It is easy to get acceptable economy. I won't say "good" economy, because modern cars are doing 5-6 l/100km in the same conditions.

Edited April 18 by GTSBoy

[Dose Pipe Sutututu]

17 hours ago, silviaz said:

lucky to get 400km on a tank lol (though that's mods for you i guess lol)

I got better economy after fitting a bigger turbo (when purely highway driving, Sydney to Forster, got down to ~8.3L/100KM), as it takes more throttle and RPM to get on boost.

[GTSBoy]

Just now, Dose Pipe Sutututu said:

I got better economy after fitting a bigger turbo (when purely highway driving, Sydney to Forster, got down to ~8.3L/100KM), as it takes more throttle and RPM to get on boost.

And also, as small as the effect may be, the larger exhaust side places a lower restriction on the exhaust flow, even when off boost. When my bigger turbo went on you could hear the difference in the exhaust note at cruise (almost everywhere actually) and fuel consumption went down a little bit.

[Dose Pipe Sutututu]

Forgot to add, that excellent economy was on street tyres, normal street alignment, I recall they were Kumho KU31.

Current motor, with the silly alignment and tyres would go nowhere near those numbers.

[PLYNX]

And what you now need is cruise control for your 'line to get even better economy . . . . or build one to suit  . . . . . . . . wait like I did . . . . . . . and never again . . . . . . . . I'd rather snort wasabi ! ! ! 

Edited April 19 by PLYNX

[Dose Pipe Sutututu]

I've got DBW, easily done via the Haltech.

Just need to feed in brake & clutch input however I'm out of inputs. Will need an IC10 dash or I/O expander to get more inputs.

[DaymoR32]

50 minutes ago, Dose Pipe Sutututu said:

I've got DBW, easily done via the Haltech.

Just need to feed in brake & clutch input however I'm out of inputs. Will need an IC10 dash or I/O expander to get more inputs.

IC7 dash is soon to be able to have inputs wired directly in.... oh wait... you dont like nintendo switches do you 😆

[Dose Pipe Sutututu]

30 minutes ago, DaymoR32 said:

IC7 dash is soon to be able to have inputs wired directly in.... oh wait... you dont like nintendo switches do you 😆

haha I held off on getting a dash for a while because I didn't like the iC7, and I knew Haltech were going to bring out another dash.

I just don't know how this will actually fit in the R33

[silviaz]

On 4/18/2024 at 4:17 PM, GTSBoy said:

I think you misunderstand. This was Greg driving from Melb to Syd (or return) at a constant 100km/h on the highway. Very little throttle movement, very little accel/decel. You should be able to get 8.5 l/100km under those circumstances (which is effectively what he reports - 50L for 600km is 8.3 l/100km).

I drive my car to & from work every day, in traffic, on a mixture of 50, 60, 90 km/h roads (and therefore at up to 110km/h!!) with traffic lights and freeway sections. 28 km each way, so about a 30-40 minute drive depending on day, direction and traffic (which is enough for the majority of the drive to be "fully warmed up". I typically get flat 10 l/100km every single week. OK, maybe 10-10.5, every single tank of fuel. RB25DET Neo.

It is easy to get acceptable economy. I won't say "good" economy, because modern cars are doing 5-6 l/100km in the same conditions.

Ah right.

[joshuaho96]

My R33 GTR gets 11.2-11.7 L/100km doing steady state 120 km/h. Is something wrong? I suspect I have an evap leak somewhere because the garage still smells like hydrocarbon fumes after a while and the O2 sensor still appears to respond pretty slowly, about a second or so peak to peak when I log via NDS1.