Lambda Discussion
 

I am starting a couple new threads for open discussion because my inbox has been flooded with PM's for this lately (which I do not mind!) but it has become hard to keep up.

So I am starting this thread for general tuning talk and questions, so please post questions and ideas regarding Fueling, AFRs, Lambda or really anything that involves a combination of the ECU, Fuel System and Delivery.

What is lambda?

Lambda is the name for the voltage output of a nernst cell exhaust gas oxygen sensor.

These nernst cells are used because as oxygen passes over the nernst cell it creates a small reaction in which a voltage is produced as a part of the oxidation process.

http://performancetrends.com/images/wide_b1.jpg

This is what the various available outputs for the most common WB I come across, the AEM WB Controller:
http://i27.tinypic.com/nei90l.jpg
http://www.aemintakes.com/instructio...-4100_inst.pdf

Uhm, I thought lambda was defined by current AFR divided by stoichiometric AFR? An O2 sensor may be used to measure the amount of O2, however it spits out voltage. Your own graph represents voltage on the independent axis and lambda on the dependent... showing that they are related but separate variables.

Thats essentially what I said, yes.

Current AFR is actually defined by Lambda times the stoich ratio.. But obviously you can manipulate the equation to figure it out from your AFRs

So obviously Gas Scale AFRs 14.64:1 is stoich. 14.64/14.64 = 1.0

Edit: Upon re-reading this I need to elaborate, I occasionally conflate the Lambda ratio with Lambda voltage, and that is my mistake. Good Call z06

So premium with 10 percent ethanol would have a lambda of 14.2?

Something like 14.13:1, but 14.2 is close enough. :wavey:

So E10 Gas would see Lambda 1.0 (stoich) @ 14.1-14.2 depending on actual gas/ethanol concentration

So a car in close loop with 10 percent ethanol gas with no knock should be looking for lambda? Looking at the chart voltage would be less than .7 or less pulling fuel. The chart is exactly what I see on the ultra gauge. As the volts are lower it pulls more fuel.

With E10 Gas for a given amount of metered air stoich (lambda 1.0) is achieved with 1 unit mass of fuel for every 14.13 unit masses of air.

Now with your example of Lambda .7, you are right that is wayyy rich. 14.13 * 0.7 = 9.89

9.89:1AFRs is pig rich, enough to cause rich knock or misfire in some cases.

On the other end of the scale, max power lean 15.4:1AFRs would be 15.4/14.13 = 1.0899 Lambda which is too lean for anything other than idle and super low load cruising.

So Lambda less than 1 is rich.

Lambda more than 1 is lean.

The nice part is this applies for all fuels. Which is how I am able to tune a cocktail of methanol, toluene, water and gas with relative precision.

The "sweet spot" changes depending on concentration, and because of the way the 4 seperate fuels enter the charge. The Meth/Water being sprayed and starting to atomize at the throttle, where the Toluene/Gas doesn't enter the stream until right before the ports dump into the bowls in front of the intake valves.

I said that wrong Lambda is 1 but the volts is .7 or less for a lambda of 1 according to the chart. The o2 volts are .675 or less but does swing higher but mostly stays .575. Its confusing to compare the volts to lambda put I see the correlation. With the warmer intake temps of the last 2 weeks my mpg is near 37 or so.

Hello,
I guess I have a lambda issue with my GD. As soon as I do things which should carry a more efficient combustion and/or efficiency (better plugs, panel filter, weapon-r header, 200 cells sport cat) my fuel consumption worsens, and even with the lightest foot possible.

If I reset the ECU and do the ILP, things improve but after some time get worse, again.

Might the cause be the O2 sensor "sensing" a leaner mixture, so willing to enrich it as well?

Should I perhaps try to remove the sport cat?

Would a FIC make me able to fix it by tricking the ECU on the O2 value fed back?

Any suggestion would be humbly welcome...

Try different gasolines first before removing back to stock. Mpg is gonna suffer in the pursuit of horsepower though and as long as there is no back fire and or light on every thing is fine.

A O2 sensor is going to look for lambda 14.7 air fuel.So the added air will richen the fuel compared to stock. Under higher loads around 70 percent the Fits ecu richen up to 11 to 1 according to papers Ive read. So the added parts will actually lean the mixture making more power and giving better mpg at higher loads.

Adding parts like intake and exhaust will only cause worse mpg at the expense to more Hp. Using a FIC would not do nothing unless you need to control bigger injectors and or add fuel for more HP.

Thanks for the feedback,
yesterday evening, after work, I frantically went to the car with my scangauge: no DTC, so I stared at the trip. It signed a horribly high value, yes, but it was the mileage (!!!!!) of that very day...! I pushed the pin and got the fuel consumption 6.8lt/100Km, i.e. 34.59mpg which is not the best but neither the worst value I got in a day. SWMBO didn't notice I had reset the trip mileage and left on that panel rather than on fuel consumption...:rotfl:

Anyway my average values are always too low (34.59mpg) for a 1.2lt. My idea behind the sport cat was to get less restriction, and an easy flow but I'll have to follow DSM shopping list to understand my engine better.

But let me ask: couldn't it be the case that - because of the sporty header and cat - the O2 is sensing too lean a mixture and is keeping enrich it?

I guess I will never know until I don't buy myself a UEGO and record the AFR... And, BTW, I already installed a set of bigger injectors (so a FIC would be useful to better extract power from them).

I found that one of my greatest mpg enemy is the "cold start time". It may last five minute and, no matter the external temp, it keeps my idling at 1500rpm and (1.5lph on scangauge), then slowly decreases to something like 750rpm. On my old 1.4 carburettors my cold start was almost zero as I kept the car on by directly driving it, rather than with "starter". And it needed maybe 30secs (at our normal temperatures) to get it idling fine.

Is it possible to alter this odd ECU cold start procedure by contracting the cold start time?

Too many things, I know, bear with me...

Thank you again.

Starting the motor in the cold is where the most fuel is wasted but necessary for proper warm up. The high rpms is whats needed to get the engine warm enough for the fuel to vaporize and minimize the washing of the cylinders and oil. You dont want to change the rpm because its set up to warm up faster. 35 mpg for a 1.2 liter is very good. Because the power to weight ratio is higher more fuel is need to produce enough Torque to move the car.

Thank you,
but there are youtube videos around on the very same engine averaging 4,8lt/100Km, i.e. 49mpg... (+40%!!!) Ok, ok, I don't know if the youtube vehicle has been driven always at steady slow speeds on highways or whatever but the declared mpg values are so lower than mine... Engine has <20Kmiles and doesn't burn oil at all. Perhaps fuel economy will improve, but I guess there's something offset in the O2 sensor (don't know which one: pre or post cat?). As soon as I reset the ECU mpg improves, then progressively worsens... hmmm...

Thanks for feedback,