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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Misfire codes, looking for some opinions



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      05-10-2014, 01:05 AM   #1
cbeers
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Misfire codes, looking for some opinions

Been getting some misfire codes recently on cylinders 5 & 6 (P29D1 & P29D2) and I'm looking for some advice/opinions.

In the next couple weeks I'll be installing everything I need to be FBO as well as getting my intake valves walnut blasted.

Question is, instead of pulling the coils on cylinders 5 & 6 and just replacing those should I go ahead and replace all 6 preemptively? Logic being that since I'm going to be putting more stress on the system going FBO, there's a decent chance other coil failures could happen.

The spark plugs and injectors only have 10k on them, so I'm not as concerned about those being the issue in my case. I've only owned the car for 2yrs, but it's probably safe to say the coils have never been replaced and that these are the original coils the car left the factory with.

Basically it boils down to, do I replace 2 coils or 6 coils?
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      05-10-2014, 08:54 AM   #2
N3m3sis
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Swap the coils around. Put 1/2 on 5/6 and vice versa. Misfire doesnt always lead to coil packs
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      05-10-2014, 09:11 AM   #3
cbeers
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Oh, I'm well aware that misfires aren't always caused by the coil packs. I was more looking for an opinion on whether, if the coil packs are actually bad, I should preemptively replace all six instead of just the two since I'll be going FBO shortly and since they have +80k miles on them too.

There's about a thousand posts on here about how to track down misfire causes, so I wasn't trying to waste peoples time asking about that. I'm more curious about what peoples thoughts are on replacing all 6 coils preemptively in my situation.
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      05-10-2014, 09:52 AM   #4
N3m3sis
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Well you can replace them, and still have a misfire. More making sure you know thats your problem...

Example: my coil packs are still oem (80k) and 100%
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      05-10-2014, 10:11 AM   #5
cbeers
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Alright, I see what you're getting at. I'll troubleshoot the coil packs today by swapping them to cyl.1&2. If they're bad I'll probably just replace those two and leave the rest as is.

After doing a little more searching, it seems the main consensus is to only replace the ones that are failing.

Thanks for the input.
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      05-11-2014, 11:22 AM   #6
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I had a leaky valve cover (cracked) and valve cover gasket that was causing me misfires. Those things, to quote a BMW tech, are their bread and butter. if you're smelling oil you should get in there with a flash light. you may have a leaky valve cover.
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