Fluctuations on lambda reading

hello guys,

i am tuning a car on m150 ecu, car is fitted with a ltc-ntk and wideband ntk sensor, the issue is on idle and cruising sometime the reading of the lambda show's some small spikes and on full throttle there is large fluctuations in the reading. Sensor is fitted about 5 inch away from the turbo into the down pipe.

please check the attached pictures, the difference between the lambda reading in the ecu and on the dyno.

note: fluctuation in injector duty cycle is due to fault lambda reading recieved by the fuel closed loop system.

what could be the issue?!

Well, what happens if you turn off closed loop and ignore the sensor? Does it still oscillate?

How do you know it's not your O2 feedback gains or the actual base tune (VE table etc) ?

Because the dyno reads the lambda just fine, will turn the closed loop system off and see how it goes

That usually happens when the Fuel Closed Loop Period has not been tuned. On the GP packages, you will find that on the Engine Systems -> Closed Loop Fuel tab. In the Closed Loop Fuel Calibrate pane, tick the Normal, Setup and Tune tags to see this table. To figure out the values for this table, turn off Closed Loop Fuel, but get a Time Graph to show Exhaust Mass Flow and Exhaust Lambda, along with Fuel Mixture Aim. Change Fuel Mixture Aim by 10% at various exhaust mass flows (ie. different engine speeds), and measure (using the time graph pause and dual cursors) the time required for the exhaust Lambda to match the Fuel Mixture Aim. Enter these values in the table.

Re-enable Close Loop Fuel, and you will find Closed Loop Fuel to do a much better job.

BTW - Andre covers this table in the first 2.5 minutes of the Closed Loop Fuel Control module.

Good Luck.

issue was due to a faulty LTC, changed it and every thing is working fine now.

thanks guys