P38A Faked mot exhaust sensor

pete12345 · 2025-06-06T08:02:03+0100

Here’s a few pics I took of readings before & after a 40miles drive I’ve got live data aswell will try to up load it later can anyone spot a major change or problems just from the pics

Mark Piercy · 2025-06-06T12:54:13+0100

If you can get the nano In graph mode (not sure). The short term fuel trims should average around 0 in the plus or minus.
The lambda sensors should have an undulating wave pattern indicating more or less oxygene pass-through the exhaust and cat.
If the short term fuel trims are running in the plus range and upwards there could be an air leak somewhere that is making it compensate for a lean mix due to un-monitored air changing the emissions and the system is trying to balance itself

kermit_rr · 2025-06-06T15:40:53+0100

Mark Piercy said:
If you can get the nano In graph mode (not sure)

i had to save the data to SD card then open in excel to do that, but maybe i just found it easier to see

pete12345 · 2025-06-06T16:02:18+0100

U lost me mark short term fuel trims what does that mean in none mechanic language cheers

Mark Piercy · 2025-06-06T17:39:45+0100

Aha, OK. So the engine in a fashion adds fuel and subtracts a bit of fuel to allow more air to go into the cats to boost the efficiency of the cats to burn the emissions off. This is why the fuel trims lift and lower and in turn the lambda sensor or exhaust sensors do a similar thing when watched on a graph.

P38A Faked mot exhaust sensor

pete12345

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Mark Piercy

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kermit_rr

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pete12345

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Mark Piercy

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