Octane issues

Rah-Vee · 08-30-2023, 09:59 PM

I have a 2009 30i 6 speed manual no engine mods. I've found that if I use 91 octane my engine will randomly throw a CEL and run rough sometimes it will go away if I turn engine off and back on. When this occurs to combat this I drive at a higher RPM to keep the engine from dying at idle. Reading the engine shows missfire in different cylinders. When I return to 93+ which is found at Shell and other gas stations the engine returns to normal, I clear the faults and it will not have any issues anymore. Does anyone know what would cause this behavior as everywhere I've read I should be able to use 91 to 94 octane gas.

B21 · 08-31-2023, 03:15 AM

Could be many things…

The inlets could be coked up with unburmt oil etc

State of the plugs?

MRCW · 08-31-2023, 02:44 PM

On all my older cars with over 80k miles I use a bottle of Techron every other tankful.

Drummer$Dude · 08-31-2023, 05:08 PM

How many miles is on your Z4 30i? I believe your engine is the non-turbo n54.

I’d start with the spark plugs, and possibly the coils aren’t up to snuff. It seems odd that 91 octane would cause issues versus 93 octane.

I replaced the fuel injectors on my 35i in 2020 because a couple of them were leaking gas into the cylinder. I bought new index 12 injectors and found the existing injectors were index 5’s.

rjahl · 08-31-2023, 05:13 PM

Quote:

Originally Posted by Rah-Vee

I have a 2009 30i 6 speed manual no engine mods. I've found that if I use 91 octane my engine will randomly throw a CEL and run rough sometimes it will go away if I turn engine off and back on. When this occurs to combat this I drive at a higher RPM to keep the engine from dying at idle. Reading the engine shows missfire in different cylinders. When I return to 93+ which is found at Shell and other gas stations the engine returns to normal, I clear the faults and it will not have any issues anymore. Does anyone know what would cause this behavior as everywhere I've read I should be able to use 91 to 94 octane gas.

What are the error codes stored in the DME?
Start there.

B21 · 08-31-2023, 05:23 PM

Apologies if it’s a 30i then it’s a N52 engine which does not suffer from coked inlets..plugs n coils are the main items..

Drummer$Dude · 08-31-2023, 06:09 PM

Quote:

Originally Posted by B21

Apologies if it’s a 30i then it’s a N52 engine which does not suffer from coked inlets..plugs n coils are the main items..

No apologies needed as I’m not well informed on anything other than the n54.

And even then there is always something new to learn.

Rah-Vee · 09-01-2023, 09:35 PM

Thanks for responses! It has 110k on the clock, N52 engine pulled codes and getting various P030X - Cylinder 1 or 3 or 6 Missfire. I've replaced all coil packs a year ago with OEM. I haven't pulled plugs yet. I'm starting to think that after many years my N52 can't handle anything besides 93 octane.

dryadsdad · 09-03-2023, 05:44 PM

I've got a new for me s30i (2011) and so have been studying the owner's manual trying to figure the electrics out. I just read today that our engines will work down to 87 octane so I find it surprising that 91 fails in yours.

I'm also surprised that 91 and 93 are available in the same area. My understanding is that in the US, the highest pump octane in general circulation is 93 or 91 in high altitudes where the engine running 93 can comfortably run 91.

Have you duplicated this or is it a one time occurance?

08-30-2023, 09:59 PM	#1
Rah-Vee Enlisted Member 12 Rep 31 Posts Drives: BMW Z4 09 30i, 2016 C450 AMG Join Date: May 2019 Location: Houston iTrader: (0)	Octane issues I have a 2009 30i 6 speed manual no engine mods. I've found that if I use 91 octane my engine will randomly throw a CEL and run rough sometimes it will go away if I turn engine off and back on. When this occurs to combat this I drive at a higher RPM to keep the engine from dying at idle. Reading the engine shows missfire in different cylinders. When I return to 93+ which is found at Shell and other gas stations the engine returns to normal, I clear the faults and it will not have any issues anymore. Does anyone know what would cause this behavior as everywhere I've read I should be able to use 91 to 94 octane gas.
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08-31-2023, 03:15 AM	#2
B21 Captain 153 Rep 611 Posts Drives: E89 Atacama Yellow 35is Join Date: May 2022 Location: Scotland..God’s own country iTrader: (0)	Could be many things… The inlets could be coked up with unburmt oil etc State of the plugs? __________________ Much modified 2011 Atacama Yellow 35is…previously a much modified 2012 Atacama Yellow 20i MSport Change history here… https://www.dropbox.com/s/8h1vabklgz...0List.pdf?dl=0 Build thread here… https://z4-forum.com/forum/viewtopic.php?t=131886
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08-31-2023, 02:44 PM	#3
MRCW Private First Class 37 Rep 121 Posts Drives: Z4 35i X1 35i Join Date: Oct 2022 Location: Florida iTrader: (0)	On all my older cars with over 80k miles I use a bottle of Techron every other tankful.
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08-31-2023, 05:08 PM	#4
Drummer$Dude Private 21 Rep 67 Posts Drives: 2009 BMW Z4 E89 35i Join Date: Sep 2020 Location: Michigan iTrader: (0)	How many miles is on your Z4 30i? I believe your engine is the non-turbo n54. I’d start with the spark plugs, and possibly the coils aren’t up to snuff. It seems odd that 91 octane would cause issues versus 93 octane. I replaced the fuel injectors on my 35i in 2020 because a couple of them were leaking gas into the cylinder. I bought new index 12 injectors and found the existing injectors were index 5’s. __________________ 2009 BMW Z4 35i 2009 Infiniti EX35 Journey AWD 2017 Lincoln MKC AWD
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08-31-2023, 05:23 PM	#6
B21 Captain 153 Rep 611 Posts Drives: E89 Atacama Yellow 35is Join Date: May 2022 Location: Scotland..God’s own country iTrader: (0)	Apologies if it’s a 30i then it’s a N52 engine which does not suffer from coked inlets..plugs n coils are the main items.. __________________ Much modified 2011 Atacama Yellow 35is…previously a much modified 2012 Atacama Yellow 20i MSport Change history here… https://www.dropbox.com/s/8h1vabklgz...0List.pdf?dl=0 Build thread here… https://z4-forum.com/forum/viewtopic.php?t=131886
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09-01-2023, 09:35 PM	#8
Rah-Vee Enlisted Member 12 Rep 31 Posts Drives: BMW Z4 09 30i, 2016 C450 AMG Join Date: May 2019 Location: Houston iTrader: (0)	Thanks for responses! It has 110k on the clock, N52 engine pulled codes and getting various P030X - Cylinder 1 or 3 or 6 Missfire. I've replaced all coil packs a year ago with OEM. I haven't pulled plugs yet. I'm starting to think that after many years my N52 can't handle anything besides 93 octane.
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09-03-2023, 05:44 PM	#9
dryadsdad New Member 3 Rep 25 Posts Drives: BMW E89, Toyota Tacoma TRD Join Date: Aug 2023 Location: South Texas iTrader: (0)	I've got a new for me s30i (2011) and so have been studying the owner's manual trying to figure the electrics out. I just read today that our engines will work down to 87 octane so I find it surprising that 91 fails in yours. I'm also surprised that 91 and 93 are available in the same area. My understanding is that in the US, the highest pump octane in general circulation is 93 or 91 in high altitudes where the engine running 93 can comfortably run 91. Have you duplicated this or is it a one time occurance?
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