Air Fuel Ratio or Lambda

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Joined: Mon Sep 17, 2018 1:54 am

Air Fuel Ratio or Lambda

Postby patrick_93 » Mon Sep 17, 2018 5:09 am

Dear All,

I use a freematcs OBD-II UART Adaptor with a Arduino mega and with the telematics shield and it's works fine for indicate the temperature of the coolant, the speed, the rpm...
My car is a BMW 523i, N53B30 engine and this engine use lean phase (with Air Fuel Ratio (or lambda) > 1 to reduce consumption) alternate with phase with lambda = 1.
But I didn't succeed to display the value of the lambda. To do it, I add in the file OBD.h, the lines:
#define PID_OXYGEN_SENSOR_1 0x38

I try several addresses like 0x34, 0x38, 0x24…

And I add in the file OBD.cpp:
result = (long int)getLargeValue(data) * 2 / 65536;
In the program.ino, I added:
int AFR; //Unit: Ratio
if (obd.readPID(PID_OXYGEN_SENSOR_1, AFR)){
lcd.print("LAMBDA : ");
lcd.printInt(AFR, 6);

On Wikipedia, the lambda is determined with the relation 2/65536(256A+B). I think that the instruction getLargeValue calculate 256A+B.
So the calculation should be correct but on the screen It's display 0 or 1 !!
Do you know how to fix the problem?

One solution could be to use the mode 6. I have a software OBDfacile and I could see the value of lambda on the PC. But I don’t know how to add a PID on the mode 6.
Do you know how to add a PID on the mode 6?
Thanks and Best regards,

Site Admin
Posts: 701
Joined: Sat Mar 01, 2014 3:15 am

Re: Air Fuel Ratio or Lambda

Postby stanley » Sat Sep 22, 2018 9:54 pm

Simply define "result" as float.

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