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N54 Engine Diagnostics - How can they be so bad

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So my N54 135i suffered

Long Crank
Rough Idle / Whole car shakes
Low Economy
Blackening of the exhaust / Carbon etc

However only once did engine light / limp mode activate

Only twice did dealer spot a code, an old code

So under Warranty the Injectors have all been replaced
The HPFP replaced Twice

For about 300 miles the car did run nice but it's old ways are creeping back

So if this car / engine management / sensors etc are so smart, how come the car doesn't know it has these faults ?

Do BMW mask them to avoid warranty work. Surely somewhere this car must 'know' it's faulty and why.

New coil pack next if warrant agrees

OR could it be worse ?? The N54 is just a bad engine ?

Advice / experiences please
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Codes only tell so much. You need to find a mechanic that remembers how to diagnose problems and NOT just read codes. These symptoms could be caused by many things, so some time will need to be spent on diagnosis. And no, these are not typical of the N54.
I would lemon the car if it's still under warranty
I'm trying. But we don't have Lemon laws as such, we do however have fit for purpose and I'm about to instruct a lawyer.

BMW UK have offered £1,500 cash ( goodwill ) in full and final or £3,500 ( $5,000 ) towards a new vehicle.

Even with the BMW contribution it still costs me to swap the car to an equiv spec 6 month newer ( N55 ) vehicle. Trying to work out a way to move out of mine to an equiv for minimal cost - problem is no one is listening !
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