N54 misfire under boost

maxwell25

New Member
Feb 20, 2024
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Car misfires in gear 3-6 at high rpm under boost at 20 psi, i have changed sparkplugs (gapped to 22) and upgraded to nexys b58 coil packs. I am big single turbo (6266)
Upgraded fuel pumps ,(dual walboro 450), i am also hood dump with no secondary 02 just the 2 on the maifold are plugged in
ANYONE have any ideas what the issue could be?
 

carabuser

Lieutenant
Oct 2, 2019
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Get some logs with the fuel mode parameter included. My money would be on fuel mode 15 as a result the tuner not knowing what he's doing.

Having no secondary O2 sensors is also a bad idea.
 

TiAgAu

Corporal
Nov 18, 2018
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08 335i
dual walbro 450? Are you running port injection? HPFP starts to drop below 1500psi from 5000rpm and goes as low as 1000psi @5400rpm
fuel trims are maxed out and running lean.
 

maxwell25

New Member
Feb 20, 2024
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dual walbro 450? Are you running port injection? HPFP starts to drop below 1500psi from 5000rpm and goes as low as 1000psi @5400rpm
fuel trims are maxed out and running lean.
I am not on port yet...my tuner keeps saying my fuel trims are good(i dont really know what they should be at), i am also runnkng e40
 

TiAgAu

Corporal
Nov 18, 2018
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Australia
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08 335i
Ideally you don't want to see your high pressure fuel pump drop below 1500psi. As i said it starts to drop @ 5000rpm and
you can the the fuel trims max out at +34 so it's at it's max of adding fuel. I'm not 100% if your at the limit of the stock fuel system running the 6266 at 21psi, Others on here will know the limit's

Do you have N20 map sensor?
 

carabuser

Lieutenant
Oct 2, 2019
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You need to have the fuel mode parameter logged to understand the causes of your misfires.

But TiAgAu is right. The trims are maxing out and your are going very lean. In fact it looks like the tuner is actually targeting 14afr which seems unwise.

If you wanted to push the limits of the fuelling you'd be better with a 12afr target, less boost and some more timing since you are at 3* in the midrange there.

You should change tuner before you end up with a cracked piston. Also consider PI or a HPFP overdrive to get the most out of that setup.