N55 #6 plug Oil Fouled

Mdilo · 06-13-2022, 02:04 PM

I have a 2011 335 N55 with 66k. This issue started with a misfire on #6 during a cold start. I pulled the plug and it was drenched in oil. I replaced all plugs and coils. I drove it a little then Checked #6 plug and it was wet with oil again. No codes and the afr and fuel trims were goos on all logs. I performed a compression test and leak down of each cylinder and they were at spec. I changed the oil and everything seemed good for about 100miles then #6 oil fouled again. I replaced the #6 injector and the valve cover and changed the oil again. After 100miles #6 was oil fouled again. I scoped the cylinders and no serious damage seen but #6 and #5 cylinders had a good amount of oil in them and the rest of the cylinders had small amounts of oil in them. I removed the engine and had it inspected and they couldn't find anything out of spec. I had a full rebuild to stock spec. Valve seals, guides, all bearing and rings etc. Well I got the engine back in and after 100 miles #6 plug had what looked to be carbon on it and #1 to #5 were clean. I put a new plug in and drove it 20 miles and now #6 is wet with oil. Compression check is at 176-180psi. The oil smells kinda like fuel...but my sense of smell is not good anymore! I just sent a sample to Blackstone. My thinking is fuel is leaking into the crankcase at hot shut offs and diluting the oil and the thinner oil is getting into #6 first for some reason. I removed all injectors and hooked them to the rail outside the engine and with 2k psi they aren't leaking but they aren't hot or stressed while I'm doing this test. I'm hoping someone had a similar issue or can give their opinion.

PearlyN55 · 04-17-2023, 04:55 PM

hey man what was the cause of this you have the exact same problem I'm trying to diagnose. I've actually gone a step further and replaced all my injectors as well but getting the same cylinder 6 fouling and have oil in 5 and 6

Mdilo · 04-19-2023, 06:06 PM

The cause of the problem was a slightly bent rod on #6.

fastboatster · 04-21-2023, 01:20 AM

Quote:

Originally Posted by Mdilo

The cause of the problem was a slightly bent rod on #6.

Would be very interesting to hear how this was discovered (the whole diag process), this is probably not too obvious.

M-technik-3 · 04-21-2023, 07:52 PM

A quick leak down test?

06-13-2022, 02:04 PM	#1
Mdilo New Member 3 Rep 28 Posts Drives: 2011 BMW 335xi Join Date: Jun 2022 Location: CT iTrader: (0)	N55 #6 plug Oil Fouled I have a 2011 335 N55 with 66k. This issue started with a misfire on #6 during a cold start. I pulled the plug and it was drenched in oil. I replaced all plugs and coils. I drove it a little then Checked #6 plug and it was wet with oil again. No codes and the afr and fuel trims were goos on all logs. I performed a compression test and leak down of each cylinder and they were at spec. I changed the oil and everything seemed good for about 100miles then #6 oil fouled again. I replaced the #6 injector and the valve cover and changed the oil again. After 100miles #6 was oil fouled again. I scoped the cylinders and no serious damage seen but #6 and #5 cylinders had a good amount of oil in them and the rest of the cylinders had small amounts of oil in them. I removed the engine and had it inspected and they couldn't find anything out of spec. I had a full rebuild to stock spec. Valve seals, guides, all bearing and rings etc. Well I got the engine back in and after 100 miles #6 plug had what looked to be carbon on it and #1 to #5 were clean. I put a new plug in and drove it 20 miles and now #6 is wet with oil. Compression check is at 176-180psi. The oil smells kinda like fuel...but my sense of smell is not good anymore! I just sent a sample to Blackstone. My thinking is fuel is leaking into the crankcase at hot shut offs and diluting the oil and the thinner oil is getting into #6 first for some reason. I removed all injectors and hooked them to the rail outside the engine and with 2k psi they aren't leaking but they aren't hot or stressed while I'm doing this test. I'm hoping someone had a similar issue or can give their opinion. Attached Images
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04-17-2023, 04:55 PM	#2
PearlyN55 Enlisted Member 3 Rep 41 Posts Drives: 2013 335i xDrive Join Date: Jul 2017 Location: New Jersey iTrader: (1)	hey man what was the cause of this you have the exact same problem I'm trying to diagnose. I've actually gone a step further and replaced all my injectors as well but getting the same cylinder 6 fouling and have oil in 5 and 6
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04-19-2023, 06:06 PM	#3
Mdilo New Member 3 Rep 28 Posts Drives: 2011 BMW 335xi Join Date: Jun 2022 Location: CT iTrader: (0)	Problem found! The cause of the problem was a slightly bent rod on #6.
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04-21-2023, 07:52 PM	#5
M-technik-3 Major 2090 Rep 1,478 Posts Drives: E30 M3, E36 M3, 328iT, 335i Join Date: Mar 2020 Location: western Ma iTrader: (0) Garage List 1995 M3 [9.00] 2007 E91 [7.25] 1988 M3 [9.50]	A quick leak down test?
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