Fuel Consumption

mitch_f1 · Postby **mitch_f1** » Fri Jan 21, 2011 10:03 pm

Just out of interest, what kind of milage does everyone get while racing? I generally get in the region of 15-18L/100km. Today at WP I got 16.78L/100km

manga_blue · Postby **manga_blue** » Fri Jan 21, 2011 11:16 pm

Fuel Consumption for Electronic Injection Engines 101.

The mixture during is normal driving (closed loop mode) should be maintained by the ECU at an ideal value of 14.7:1 air:fuel. The ECU uses the oxgen sensor in the exhaust pipe to ascertain what the mixture is. It cycles the mixture in a range of about 14.3 to 15.1, which happens to give the cat convertor the best operating conditions, as well as best economy

So the Oxygen sensor is the key sensor for the management of consumption. When mixture is lean then the Oxy sensor outputs a low voltage. Rich mixtures give high voltage. As the oxy sensor ages then its output voltage gets lower and lower. That misleads the ECU into thinking the mixture is leaner than it really is. The ECU compensates by making it richer and richer. This is what buggars up fuel consumption. Every other engine problem that might theoretically affect fuel consumption is secondary to the ECU working with the oxygen sensor to work out what's going on inside the engine.

The economic life of a single wire sensor in an NA6 is about 60,000km, in a 4 wire NA8 or NB8A sensor it's 80,000km. More modern 4 wire planar sensors in the NB8B can be good for 160,000km. Some will last longer, some will last less. After those periods the payback in fuel consumption normally covers the costs of a new sensor.

lee · Postby **lee** » Sat Jan 22, 2011 12:51 am

I've been keeping a tab on my fuel consumption since I bought my car 4 weeks ago (I've filled up 8 times since then!). My average fuel consumption is 8.55L/100ks, with the lowest being 7.83L/100ks. I've always used Premium 98, with the most efficiency being found from Castrol fuel. I'm getting an average of 530 ks on a tank.

If anyone is interested, I can post the Excel spreadsheet I'm using.

rascal · Postby **rascal** » Mon Jan 24, 2011 8:45 am

mitch_f1 wrote:Just out of interest, what kind of milage does everyone get while racing? I generally get in the region of 15-18L/100km. Today at WP I got 16.78L/100km

Depends on which track you are at, as different tracks have varying periods of full throttle, different gears used, etc, etc..

At Phillip Island I get about 190kms out of a full tank. So that's just over 25 l/100km..
On the road I get about 500kms out of a tank so 9l/100km..

Guran · Postby **Guran** » Mon Jan 24, 2011 9:29 am

mitch_f1 wrote:Just out of interest, what kind of milage does everyone get while racing? I generally get in the region of 15-18L/100km. Today at WP I got 16.78L/100km

What rascal said! My record is 19.3L/100km after doing ~150km in a day around Eastern Creek and minimal kms on the street getting to/from the servo at the start and end of the day. Fuel consumption during trackdays is not something you really want to think much about ... apart from the risk of running dry! At the other extreme, I've seen 7.0L/100km after a looooong stretch of 100km/hr highway cruising. My long term average, including trackdays, is 10.1L/100km after 18,000km.

snshami · Postby **snshami** » Mon Jan 24, 2011 10:35 am

Out of interest how much do oxygen sensors on an NA8 cost. Can they be changed by the typical backyard mechanic?

manga_blue wrote:Fuel Consumption for Electronic Injection Engines 101.

The mixture during is normal driving (closed loop mode) should be maintained by the ECU at an ideal value of 14.7:1 air:fuel. The ECU uses the oxgen sensor in the exhaust pipe to ascertain what the mixture is. It cycles the mixture in a range of about 14.3 to 15.1, which happens to give the cat convertor the best operating conditions, as well as best economy

So the Oxygen sensor is the key sensor for the management of consumption. When mixture is lean then the Oxy sensor outputs a low voltage. Rich mixtures give high voltage. As the oxy sensor ages then its output voltage gets lower and lower. That misleads the ECU into thinking the mixture is leaner than it really is. The ECU compensates by making it richer and richer. This is what buggars up fuel consumption. Every other engine problem that might theoretically affect fuel consumption is secondary to the ECU working with the oxygen sensor to work out what's going on inside the engine.

The economic life of a single wire sensor in an NA6 is about 60,000km, in a 4 wire NA8 or NB8A sensor it's 80,000km. More modern 4 wire planar sensors in the NB8B can be good for 160,000km. Some will last longer, some will last less. After those periods the payback in fuel consumption normally covers the costs of a new sensor.

jerrah · Postby **jerrah** » Mon Jan 24, 2011 11:36 pm

22mm spanner and a plug. It's a bit awkward to reach is the only thing.

wilch · Postby **wilch** » Tue Jan 25, 2011 5:44 am

snshami wrote:Out of interest how much do oxygen sensors on an NA8 cost. Can they be changed by the typical backyard mechanic?

manga_blue wrote:Fuel Consumption for Electronic Injection Engines 101.

The mixture during is normal driving (closed loop mode) should be maintained by the ECU at an ideal value of 14.7:1 air:fuel. The ECU uses the oxgen sensor in the exhaust pipe to ascertain what the mixture is. It cycles the mixture in a range of about 14.3 to 15.1, which happens to give the cat convertor the best operating conditions, as well as best economy

So the Oxygen sensor is the key sensor for the management of consumption. When mixture is lean then the Oxy sensor outputs a low voltage. Rich mixtures give high voltage. As the oxy sensor ages then its output voltage gets lower and lower. That misleads the ECU into thinking the mixture is leaner than it really is. The ECU compensates by making it richer and richer. This is what buggars up fuel consumption. Every other engine problem that might theoretically affect fuel consumption is secondary to the ECU working with the oxygen sensor to work out what's going on inside the engine.

The economic life of a single wire sensor in an NA6 is about 60,000km, in a 4 wire NA8 or NB8A sensor it's 80,000km. More modern 4 wire planar sensors in the NB8B can be good for 160,000km. Some will last longer, some will last less. After those periods the payback in fuel consumption normally covers the costs of a new sensor.

Unsure of cost for the MX5. But yes, it can be done. You just need to have the right sized spanner, which can actually be hard to find depending on stock levels at your local Repco.

justinowell · Postby **justinowell** » Thu May 26, 2011 3:03 pm

manga_blue wrote:Fuel Consumption for Electronic Injection Engines 101.

The mixture during is normal driving (closed loop mode) should be maintained by the ECU at an ideal value of 14.7:1 air:fuel. The ECU uses the oxygen sensor in the exhaust pipe to ascertain what the mixture is. It cycles the mixture in a range of about 14.3 to 15.1, which happens to give the cat convertor the best operating conditions, as well as best economy

So the Oxygen sensor is the key sensor for the management of consumption. When mixture is lean then the Oxy sensor outputs a low voltage. Rich mixtures give high voltage. As the oxy sensor ages then its output voltage gets lower and lower. That misleads the ECU into thinking the mixture is leaner than it really is. The ECU compensates by making it richer and richer. This is what buggars up fuel consumption. Every other engine problem that might theoretically affect fuel consumption is secondary to the ECU working with the oxygen sensor to work out what's going on inside the engine.

The economic life of a single wire sensor in an NA6 is about 60,000km, in a 4 wire NA8 or NB8A sensor it's 80,000km. More modern 4 wire planar sensors in the NB8B can be good for 160,000km. Some will last longer, some will last less. After those periods the payback in fuel consumption normally covers the costs of a new sensor.

I didn't mean to make a bump, but I randomly came across this thread after searching for knowledge about oxygen sensor. I just want to say that this thread helped me a lot with regards to fuel consumption basics. Thanks for sharing mate.

bundy_harry · Postby **bundy_harry** » Thu May 26, 2011 5:10 pm

Just a note on fuel consumption I really dont care about how much fuel cost as mine only gets dríven on weekends...

93 NA6 166,000 km on the clock spirited runs through the mountains to Bathurst recently has seen me returning fuel figures of 6.3L/100km, last fill up was just a fraction under 38 litres for a fraction more than 600km.

cheers
Harry

Dweezle · Postby **Dweezle** » Thu May 26, 2011 5:22 pm

WOW!!
Best I've done is 7.1L/100.
Travelling to QLD, 100km/h flat roads.

manga_blue · Postby **manga_blue** » Thu May 26, 2011 6:35 pm

justinowell wrote:I didn't mean to make a bump, but I randomly came across this thread after searching for knowledge about oxygen sensor. I just want to say that this thread helped me a lot with regards to fuel consumption basics. Thanks for sharing mate.

Thanks Justin, but you've just reminded me that I still need to fix it.

All that I said applies if and only if the engine is properly warmed up and the ECU believes that it's properly warmed up. If the ECU detects that it's not at full operating temp then it may richen the mixture (and hence buggar the full consumption).

There are two ways this could happen:
a) the engine is truly not warm enough. Usually because the thermostat is jammed open, missing or opening at too low a temperature. Check this by heating your thermostat in a saucepan of water with a thermometer in it. Mazda specs are for initial opening from 83.5oC with full opening at 100oC.
b) the engine coolant temp (ECT) sensor is misreading. Check this by adding the ECT to the saucepan and measuring resistance across it as it heats up. Mazda specs are -20oC : 14.6-17.8 k ohms, 20oC : 2.2-2.7 k ohms, 80oC : 0.29-0.35 k ohms

Hjt · Postby **Hjt** » Thu May 26, 2011 8:14 pm

Thanks for all the useful information, I have two questions if that is okay.

I have a 93' NA6 and i'm currently running RON98 from either Caltex or BP

And also the fuel sensor, besides Mazda who would stock replacement parts>?

mitch_f1 · Postby **mitch_f1** » Thu May 26, 2011 9:46 pm

SO i worked out that I got 6.5L/100km coming back from Goulburn, and 9L/100km on a spirited drive through Wisemans Ferry area

Postby **NitroDann** » Thu May 26, 2011 10:10 pm

I think its worth noting that what magna blue said about fuel comsumption is pretty general.
Maximum fuel economy is not found at 14.7:1. Less fuel than 14.7:1 is used for max economy. The b series engine can run up to about 17:1 before missfiring on petrol and a little over 18:1 on E85. Some lean burn engines, like the prius and most hondas can run as lean as 22:1 comfortably due to very good swirl, this is due to good combustion chamber design.
Having said that both the B6 and BP make the most torque per gram of fuel (and therefore best efficiency) at around 15.8:1. So even though you can run leaner,like closer to 18:1, the engine starts making so little power you need more throttle and therefore fuel to overcome it.

My fuel economy, about 6km per litre.

Dann