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McLaren 12c 2012
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Discussion Starter · #1 ·
Dear all people in the know, @M-Engineering

Regarding fuel trim corrections on mclarens, is it normal to see such STFT swinging? Is the OEM map that bad? My car runs perfectly well with stable STFTs on idle but with normal driving/throttle inputs im seeing this...Your input would really be appreciated.

Thanks

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12C and 650S are a bit "dirtier" than the rest of the McLaren family as far as fuel trims go. WOT and idle seem fairly steady in relation to the trims at cruise, but at cruise they do have 20-30% swings.

However, there does exist a table within the 12C to adjust for oscillations in fuel trims based on engine speed and effective pulse width of the injector. Pulsing injectors can cause pressure oscillations in the fuel rails as well. This tends to be related to harmonics at certain engine speeds and pulse widths and the impact is greater with larger injectors that can inject more mass in a shorter pulse. Some of this stuff can be cleaned up using this table.

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Typically setting up a histogram based on fuel trims can help iron this out some. The value is a scaler that is multiplied against the calculated effective pulse width to give you a new pulse width out to the injectors. So say at 5000RPM and 3ms your output would be changed from 3.00ms to 3.13ms.
 

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McLaren 12c 2012
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896 Posts
Discussion Starter · #3 · (Edited)
Got it, thanks a lot for your reply, based on my LTFTs being within spec, around 3.6 + and -3 negative I knew there was nothing to worry about but the STFTs do seem pretty messy, I get the impression that the mclaren stock mapping on these models is not the best and I am sure you will agree.

What is confusing though is that the LTFTs work on a average for STFTs... So I would have thought that the LTFTs would have been more effected by these crazy STFT numbers... ? Is there a reason why they are so messy? Lazy mapping? It even tripped my fuel trim stock safety once. I think that was just after I cleaned my air filters and hasnt done it since.

Thanks a lot @M-Engineering for your time.
 
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