Excess Fuel Consumption

[pixel8r]

You wouldn't believe how hard it is to convince some people (not anyone on here) that the computer is the reason it runs rich, and pushing more air in just makes the computer dump more fuel in.

Maybe on old cars before ecu's more airflow = leaner fuel mix but modern cars seem to be too "smart" for that.

The standard fuel map means that it will keep getting richer and richer until eventually it'll switch to whats known as R&R (Rich and Retard) mapping, making your car run very sluggish - its a failsafe measure to stop it running lean. Also, I believe there is some sort of boost/fuel cut if you go crazy on boost - there definitely is on the RB25's, not sure about VQ's. Happened to me just running 12psi on my last stagea, nearly sends you through the windscreen cos you're at full throttle & max acceleration when it happens.

On the RB25's tuning was as simple as a piggyback ecu to modify the airflow meter signal to the ecu - therefore tricking it into thinking there was less air coming in than there actually was, and therefore you'd get less fuel. I'm talking about the Apexi SAFC (and SAFC-II and SAFC-NEO). Unfortunately these dont appear to work too well on the M35 - seems the latest cars are too smart yet again and we need to go further to tune them.

As for making it run lean without changing the ecu - well, pretty much it aint gonna run lean until you're sucking in more air than the injectors/fuel pump can cope with (ie. they cant supply the necessary amount of fuel to match) - but the ecu will have limits built in that will cut in before this can happen anyway (see R&R mapping above - or search this forum for R&R). Pretty much the only way to improve the air/fuel ratios is by messing with the ecu in some way. I'd be glad to be proven wrong though...

[Houdini]

This may be a silly question....but.... I have an Apexi pod which theorectically would allow more air in (it sounds like a jet sucking in air when I put the foot down) then is the ecu adding more fuel, therfore my fuel economy sucks worse?

I have a new exhaust and I've noticed a light layer of black soot like material coating the insides of the pipe now - that means running rich right?

[Bis-e Bee]

Remapping of the ECU is one way (the way I'm looking at) or a E-Manage Ultimate or similiar piggyback system.

Don't know what other ways it can be safely achieved.

[zei20l]

This may be a silly question....but.... I have an Apexi pod which theorectically would allow more air in (it sounds like a jet sucking in air when I put the foot down) then is the ecu adding more fuel, therfore my fuel economy sucks worse?

I have a new exhaust and I've noticed a light layer of black soot like material coating the insides of the pipe now - that means running rich right?

actually a pod might decrease fuel comsumption as sucking through the standard airbox takes more work than the pod. that said, hotter air has less energy (yes i know thats technically wrong) than colder air which your pod is sucking in, unless you have a heat sheild.

youll always get soot on a new exhaust, carbon is produced when you burn a fuel. thats what it is. but yes these cars run very rich from factory!

[pixel8r]

Yeah I think opening it up and helping it breathe with a pod/exhaust etc will help it run better etc, and definitely will increase power, but yeah its hard to say if it would help much with fuel economy without any tuning. You may well get fuel economy benefits purely because there's less pressure and therefore everything is more efficient...but any gains here would be nothing compared to what you'd see if it was tuned properly.

With my last stagea I managed about 2-3L/100km better fuel economy just in tuning alone. Some of that was due to advanced ignition timing, which makes me wonder if the same can be done even with just the stock ecu. The SAFC I had also helped to reduce fuel usage by smoothing out the air/fuel ratios and keeping them from running too rich.

Has anyone tried adjusting the base ignition timing on a dyno? is there enough safety margin to increase it a little even without mods?

I've been tempted to do this but in the back of my mind I just know that any saving in fuel it might bring would be wiped out by the cost of the dyno session...

[zei20l]

if youre getting a tune for some reason or other, then i guess they can check the timing

i might check my timing after i do an oil change this weekend - assuming i can be stuffed - and see what the base timing is.........

[iamhe77]

actually a pod might decrease fuel comsumption as sucking through the standard airbox takes more work than the pod. that said, hotter air is less dense than colder air which your pod is sucking in, unless you have a heat sheild.

youll always get soot on a new exhaust, carbon is produced when you burn a fuel. thats what it is. but yes these cars run very rich from factory!

Fixed

Edited June 12, 2009 by iamhe77

[zei20l]

haha i knew that, but a lot of people dont!

hence why i said energy, but yes cooler more dense air can be compressed better thus having more energy

[Houdini]

Resurecting this old thread becaus the rsults of my latest fill up are in. Trip computer said 50km's remaining and I'd done 450km's, looking good...

than my results - 14.1 litres per 100km's!

I'm not sure what happened the first time, maybe my user error on the odometer or something ??

Edit: oh yeah BTW my first big trip in my diesel X-Trail netted 6.1 litres per 100k's

Edited July 4, 2009 by Houdini

[andy65b]

Yeah, but I know the X-trail is not as much fun to drive...

[zei20l]

im not sure how true this is, but, i was told even changing fuel types (brands) can affect consumption due to additives/detergents in the fuels. your car was probably run on a particular type of fuel (people get into rhythms) in japan, over here you have used something else and the car needs to get 'used' to it....... im told that shell fuels leave build ups in the fuel system and when you change to something else, you wont get as good consumption, thus you go back!

anyway, not sure how true it is, but its food for thought!

[iamhe77]

Dunno about Shell being a "dirty" fuel, the only 98 fuel that leaves black puffs out my exhaust is Vortex98 (Caltex).

Shell Vpower, BP Ultimate & Mobile Synergy 8000 do pretty much as well as each other in my car.

In case you didn't catch it, check out Ash's thread

The Inside Look… Ferrari & Shell - Formula 1

"A key point to consider is not all the batches are the same.

As the development goes on through the year during meets, given there is no in-season testing now, one batch is not necessarily the same what will be next. Ferrari might also be chasing a specific result from the fuel which could play key parts in a championship decider as it has before with a race win for Schumacher as he gained another lap over everyone else due to fuel composition."

I know that it is mainly about F1, but if the fuel batch can vary at F1 level...

[Jetwreck]

im told that shell fuels leave build ups in the fuel system

anyway, not sure how true it is, but its food for thought!

Might have to back you on this Ian....when I was racing Jetski's we stopped using Shell for that very reason.

[Bis-e Bee]

im not sure how true this is, but, i was told even changing fuel types (brands) can affect consumption due to additives/detergents in the fuels. your car was probably run on a particular type of fuel (people get into rhythms) in japan, over here you have used something else and the car needs to get 'used' to it....... im told that shell fuels leave build ups in the fuel system and when you change to something else, you wont get as good consumption, thus you go back!

anyway, not sure how true it is, but its food for thought!

If you have been using shell is there anything you should put through the engine to remove the build up?

I think Nissan put some injector cleaner in for me when it was serviced but is there anything else that can clean the gunk out that dodgy fuel companies insert in to their overpriced dodgy fuel?

[zei20l]

just use another fuel for ages, eventually it will just get rid of the build up. i only use BP fuel now after only ever using shell for a long time. i rekon the M35 runs much better on the BP than the shell

[pixel8r]

just use another fuel for ages, eventually it will just get rid of the build up. i only use BP fuel now after only ever using shell for a long time. i rekon the M35 runs much better on the BP than the shell

I always thought this too. Lately I've been using shell mainly for the 4c/litre discount, but it definitely doesn't run as smoothly as with BP. It is noisier with shell fuel, hard to explain. A friend who used to work at the refinery was telling me shell fuel is the best blah blah and reckoned it is louder because it has more power with shell. Not sure if this is true or not.

BP ultimate just seems to run quieter/smoother. I wouldn't say its worse than shell for either power or fuel consumption...but then I haven't done a whole lot of testing. Didn't notice much difference to fuel economy after switching from bp to shell. If anything it got worse, but this could just as easily be attributed to my driving patterns. There are always other factors so very difficult to do a fair comparison just on week-to-week usage.

Caltex 98 made the car run more sluggish, wont be touching that again.

[[[d a n n y]]]

okay guys intresting find yesterday..

decided to close off my airbox again.. (that little opening in the front of the box)

obvously the car was quiet again

but i noticed the car seem to pull better and was really smooth on the power delivery compared to the airbox open

also the fuel consumption was better. i was mostly over the 10L mark on the leaf..(Screen)

i will do another full tank comparo run with airbox closed but it's noticeable

Edited July 5, 2009 by [[d a n n y]]

[zei20l]

theres no way in hell im closing the airbox off!! i need that sound!! haha

but let us know how you go. as a comparison, my S15 got around 50km per tank MORE when i put a pod filter on (only mod) putting an exhaust on made me lose the 50km per tank. but it hauled ass

id like to see how it affects consumption if you can please post up and results you get mate

[[[d a n n y]]]

yeah already filled up today should be empty in about 3 days lol

but IMO

More air = More Fuel??

[zei20l]

yeah thats generally the case