Thread: How do I improve Fuel Consumption?

Oxygen sensors cannot modify the entire map. They can only as I understand
it apply one correction value to the entire map when running in closed loop
mode. Essentially a best-fit.

No they continuously feed back to the ECU which corrects each bank continuously. They average mixture around stoicometric but . You can see it using an analogue multimeter or simple LED logging device where you will see the mixture continuously changing rich/lean. ( I fitted a third O2 sensor to mine to monitor).
And yes closed loop only by definition but this is up to about 80% throttle. If you are concerned with fuel economy , I don't think that 100% throttle will be used very often in the real world, not by me anyway.

IMHO it is a great "set and forget" mod , whereas if anything changes in your sensors , the tune will be altered.

BUT I must add that there are far more gains to be had by manipulating the advance curve , and that is what more modern ECUs do. The RV8 can take up to 45-50 degrees total advance on light throttle and the "rest of the world" Australian tune has nothing like that.. The greatest improvement with mine came from the Unichip which sets a digital "vacuum" advance curve. AFAIK it could do the whole curve vacuum and cenrifugal like a Megajolt , but I wonder at dyno operator's experience ( and the cost to get it right) when car manufacturers spend millions on just this and starting strategies.

BTW , the graphs I have seen of fuel usage vs AF ratio show VERY minor gains over about 15:1 , AFAIR only a couple of % to 16:1 , wheras you are on the very edge of driveability there.
Regards Philip A

Originally Posted by garrycol

Hang on there Dougal - the OP is reporting 3.5km/l (28.5l/100km) crossing the Simpson Desert not driving down a sealed highway.

I did miss the Desert reference. You'll have to forgive me, no Deserts here.

Dougal I took this reference from a Honda tuning site but it holds true for most if not all engines.

This graph shows relative fuel consumption and manifold pressure
versus air/fuel ratio. Note that the manifold pressure increases as the air/fuel
ratio is made leaner. To obtain the same power output with a leaner mixture,
you have to use more throttle. Generally, fuel consumption decreases as the
mixture is made leaner. Eventually the increase in manifold pressure offsets
the reduction in fuel flow and fuel consumption increases once the mixture is
leaned past 15.7:1.


At the stoichiometric air/fuel ratio, fuel consumption is around
two percent higher than optimum. Air/fuel ratios richer than stoichiometric
sharply increase fuel consumption so that running 13.5:1 results in eight
percent more fuel consumption than stoichiometric. This is why it's important to
have a correctly functioning oxygen sensor.

Read more: Fuel Economy Tuning - Tech Review - Honda Tuning Magazine

Read more: Fuel Economy Tuning - Tech Review - Honda Tuning Magazine

Originally Posted by PhilipA

BTW , the graphs I have seen of fuel usage vs AF ratio show VERY minor gains over about 15:1 , AFAIR only a couple of % to 16:1 , wheras you are on the very edge of driveability there.
Regards Philip A

This is the interesting part. Efficiency peaks around 16:1, but depending on the engine there can still be gains made in reducing pumping losses by running the throttle further open at cruise (side effect of a leaner mixture). The larger the engine, the more there is to gain in pumping losses. A 3.9 V8 has quite different tradeoffs in this area to say a 2 litre 4 cylinder.

I haven't found any drivability issues (lean misfire etc) yet from running lean and I decided I'd rather err on the lean side of 16 than the rich side for cruise (16.5 vs 15.5). I'd love to be able to log fuel consumption in real time to compare, but it's simply not worth the effort to set an alternative system up and calibrate it. This V8 is a temporary resident at my place.

Though there was a thread was recently where someone was getting similar consumption on the road.

Really, if the V8 is tuned correctly and in good condition, playing around with ECUs, exhausts etc may make an improvement but it is not going to be much of an improvement.

Garry

Originally Posted by garrycol

Though there was a thread was recently where someone was getting similar consumption on the road.

Really, if the V8 is tuned correctly and in good condition, playing around with ECUs, exhausts etc may make an improvement but it is not going to be much of an improvement.

Garry

The bit in bold is the crux of the problem with 20 year old engines.