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Discussion Starter · #1 ·
Hi! :wave:
LR3 4.0 V6 with new genuine air flow meter installed.
Drives better than before,but these contradictary fault codes won't cease coming back.
Have no idea what the cause could be .....
Any clue ?
Thanks.
 

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It really isn't weird on this engine management system. Fuel trims are calculated by both up and downstream oxygen sensors.

So if you are having incomplete combustion, and not burning all of the fuel with all of the air on each cycle, the upstream sensors will read a lean condition, and the down stream sensors will read a rich condition.

The best way to know what is going on with the fueling system on this, due to its complexity, is to have the Adaptive Fuel Trims read(which requires dealer grade diagnostics) and will show both what the long term(upstream) trims are, and the sub-feedback adjustments(downstream) are, at various engine speeds and loads.

Generally though, this is caused by incomplete combustion, and a proper tune up(spark plugs and wires - use factory/Motorcraft plugs on the V6) will take care of it.

Also, if the MAFS was just replaced, you may only be looking at one issue(be it rich or lean) and the fuel trims have not reset since the repair of the MAFS. Preforming a Hard Reset will reset the engine adaptions, and allow it to fuel from a base, which along with clearing the fault codes, will show you what is happening right now.
 

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Discussion Starter · #4 ·
Hard reset makes a difference,drives even better.
But still threw lean codes occasionally.
Then I tried ECU reflash with updated firmware.
Everything is fine now for a long while.:D
 
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