Guess what, you all now have a built-in wideband AFR meter

[rkneeshaw]

The MS45.1 cars like the ZHP came with wideband O2 sensors in the pre-cat locations.

The problem is, the DME only reports the voltage of these wideband O2 sensors, and not the AFR or lambda.

But I've calculated the formula that will convert the pre-cat O2 sensor voltages to lambda, and then its an easy calc to get AFR (lambda * 14.7 = AFR).

So if you want to know how rich or lean you are running at any time, even during wide open throttle, pick up yourself a cable and a copy of Renovelo Bytelogger (http://www.renovelo.com/bytelogger/). Then go for a drive and log some data, and make sure you are logging your pre-cat O2 sensor voltages, either bank 1 and/or bank 2.

Once you have your log, which will be a nice neat CSV file, open it in Excel and use this formula to give yourself a lambda value for those Pre-cat o2 voltages:

=0.684562+(<Pre-cat O2 Voltage>*0.205987)

Or if you want to go straight to AFR:

=(0.684562+(<O2voltage>*0.205987))*14.7

These calcs will get you an AFR reading that should be pretty much spot on.

Enjoy!

PS Bytelogger is an awesome diagnostic trouble code reader too. It not only reads and clears all trouble codes, but it reports additional freeze frame data that was captured at the time the code was triggered. So you get a data logger and a code reader/clearer in one package, I highly recommend it.

[BMWCurves]

Jokes aside, this sounds cool! Thanks for the info

[rkneeshaw]

lol william, until now if you wanted to know how rich or lean your car was running (e.g. Air-to-Fuel Ratio, or AFR) you had to buy a dedicated wideband O2 sensor, weld in a bung into your exhaust, buy a wideband controller, wire it into a 12v source, and install a AFR gauge.

Now you just buy a cable and software and you're done.

And you can log that data and see how your car is running over time.

Very beneficial for anyone who tunes their car, buys a tune, or does something like a turbo or supercharger

[BMWCurves]

I surmised as much, just joking around

[Oli77]

The UltraGuauge II reports lambda values (no idea what they mean).

They report:
Bank 1 Wide 0xygen Sensor 1 Lambda (voltage based)***
Bank 1 Wide Oxygen Sensor 2 Lambda (voltage based)(UG Plus & UG MX only)***
Bank 2 Wide 0xygen Sensor 1 Lambda (voltage based)***
Bank 2 Wide Oxygen Sensor 2 Lambda (voltage based)(UG Plus & UG MX only)***

Is that the same as the Lambda you are talking about (and for the noob in me, what is lambda?)

[RITmusic2k]

Gonna answer your question in two ways because I'm not sure which part you were unsure of:

Lambda in this case represents the ratio of actual air-fuel mixture compared to the stoichiometric ratio. 'Lambda' is just the variable they decided to use when defining it... it could have been 'x' or 'Oli77' or anything.

As far as what the ratio actually means, let's first define the stoichiometric ratio. This is when, for a given fuel, there is exactly the right amount of oxygen available to perfectly and completely combust all fuel present - no more, no less. This is defined as Lambda = 1. If you have more fuel than air, lambda drops below 1.0, which is equivalent to running rich. Conversely, if there's too much air, lambda goes higher than 1.0 and you're running lean.

[danewilson77]

Gonna answer your question in two ways because I'm not sure which part you were unsure of:

Lambda in this case represents the ratio of actual air-fuel mixture compared to the stoichiometric ratio. 'Lambda' is just the variable they decided to use when defining it... it could have been 'x' or 'Oli77' or anything.

As far as what the ratio actually means, let's first define the stoichiometric ratio. This is when, for a given fuel, there is exactly the right amount of oxygen available to perfectly and completely combust all fuel present - no more, no less. This is defined as Lambda = 1. If you have more fuel than air, lambda drops below 1.0, which is equivalent to running rich. Conversely, if there's too much air, lambda goes higher than 1.0 and you're running lean.

I thought you were a musician.



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[rkneeshaw]

The UltraGuauge II reports lambda values (no idea what they mean).

They report:
Bank 1 Wide 0xygen Sensor 1 Lambda (voltage based)***
Bank 1 Wide Oxygen Sensor 2 Lambda (voltage based)(UG Plus & UG MX only)***
Bank 2 Wide 0xygen Sensor 1 Lambda (voltage based)***
Bank 2 Wide Oxygen Sensor 2 Lambda (voltage based)(UG Plus & UG MX only)***

Is that the same as the Lambda you are talking about (and for the noob in me, what is lambda?)

Yes, that is the lambda I'm talking about, at least in concept. BMW does not offer lambda values over the OBDII port, and in fact I've found that our BMW's don't even show the pre-cat O2 voltages over standard OBDII protocols. You have to use a BMW-aware scanner, such as ByteLogger, to get the pre-cat O2 sensor voltages, and the formula I posted here to get lambda.

[rkneeshaw]

I caught a slight miscalculation. I've updated the formula in the first post to this:

Lambda = 0.684562 + (<Pre-cat O2 Voltage> * 0.205987)

[Oli77]

Cool! Thanks both for clarifying this. I will now look at my lambda values and know what they report.