[diceman]

2005 325xi

P0303 code (cylinder 3 misfiring)
Over past 2 weeks, replaced all coils, plugs, o2 sensors, maf switch, air filters.
Car has 165k miles so a lot of this stuff needed replacing anyway.

Trouble is I am now seeing that the number 3 sparkplug threads are coated in oil when I remove it to inspect.

Can a blown valve cover gasket allow oil to seep into the sparkplug chamber from the BOTTOM?

My mech is a classic car specialist so maybe not so familiar with BMW, but insists that failed o-rings or valveguide issues are the only things that would put oil at that spot and a failed VCG would not do that.

I really would rather not replace the engine...the car ran like a top and in a lot of ways is more fun to drive than my 2011 325xi!!
Could a bad VCG throw a p0303 code?

Would appreciate some comments on this.

Thank you!
Dave

[ctuna]

I would swap out the coil first.
From what I understand oil on the coil is not good for it.
Is is possible oil was spilled while filling as the third cylinder
is right in the middle .
Also is the plug tip fouled ?

[diceman]

I installed all new coils and plugs x 6.
Plug tip still looks brand new.
Threads coated in oil.

Question is, would oil seep up from the bottom from a bad valve cover gasket?
Would that cause the 303 code?

Thanks,
Dave

[335NJ]

Maybe pull the plug from cyl. 3 and post a picture of it. Oil on the plug/coil will cause a problem i'm sure.

[diceman]

here is a pic of the new sparkplug after inserting then removing to inspect it.
Oil on the threads. Here is also a pic of the nbr 3 looking down the sparkplug shaft.

my question is still: would a leaky valve cover gasket cause a p0303 code?
How is oil getting up into the plug shaft from the bottom?
Would a valve cause that or do i have bad rings or valve guides?

[diceman]

here is a pic of the new sparkplug after inserting then removing to inspect it.
Oil on the threads. Here is also a pic of the nbr 3 looking down the sparkplug shaft.

Teh final pic are the original plugs, coils and o2 sensors that i replaced.
The dirtiest coil is from nbr 3.

This car has ove 160k miles and im not the original owner so I dont know what has been replaced prior.

my question is still: would a leaky valve cover gasket cause a p0303 code?
How is oil getting up into the plug shaft from the bottom?
Would a valve cause that or do i have bad rings or valve guides?

[galahad05]

I dunno, mine looked like that (335i with DEFINITELY a leaking valve cover gasket). For me it was plug #6. Quite a bit on the threads.

But the critical point is this: if it's oil seeping down from the valve cover area, you should be able to see it. You may have to look carefully, or even use that fluorescent dye + blacklight trick, but you should be able to see it, outside of the plug. If you cannot find any, then obviously it won't be the VCG where your leak is coming from.

[galahad05]

I suppose you could also borescope the combustion chamber through the plug hole, assuming you have access to a borescope with a small enough end to it. See what the combustion chamber looks like.
That much oil, if it's coming "up" from the combustion chamber, is going to show lots of oil in the chamber proper.

[diceman]

right, the oil is definitely not coming down from the top of the plug.
If a borescope is showing oil in my engine, what is the diagnosis?

O-rings? Valve guide issues?

Do I bother doing a repair on it, or just go out and get an engine replacement for $2k??

Thank you,
Dave

[galahad05]

Originally Posted by diceman

right, the oil is definitely not coming down from the top of the plug.
If a borescope is showing oil in my engine, what is the diagnosis?

O-rings? Valve guide issues?

Do I bother doing a repair on it, or just go out and get an engine replacement for $2k??

Thank you,
Dave

Wait, let's just make sure of this first. Are you saying that, for example, the coil boot for #3 was bone dry?

[galahad05]

Okay, let's say you have real oil control problems in cylinder #3.
First test to do (assuming your classic car mechanic hasn't already done it): leakdown.
This tells you if you have compression problems that could very well be worn or I suppose broken piston rings.

Also, from a cold start, do you get blue/black smoke that goes away once the engine starts to warm up? That is a classic symptom of a worn valve guide.

EDIT: regarding the compression test. You can have your mechanic do a wet compression test to see if you have worn rings. This is where you warm up the engine, do a compression test, then squirt a little bit of oil into the spark plug hole. If the compression goes up a fair bit, you have worn rings.

Again though, you should be VERY sure that you aren't seeing oil leaking down into the spark plug hole from the top of the engine (i.e. bad valve cover gasket or a cracked valve cover).

[Efthreeoh]

I think this is a simple case of the valve cover seal around the plug hole is leaking in cylinder No.3. The oil sits at the bottom of the plug hole. When you unscrew the plug the oil gets on the threads. The oil is not going to go against gravity and leak up from the cylinder and seep into the plug threads. Any oil in the cylinder would burn off.

[galahad05]

Originally Posted by Efthreeoh

I think this is a simple case of the valve cover seal around the plug hole is leaking in cylinder No.3. The oil sits at the bottom of the plug hole. When you unscrew the plug the oil gets on the threads. The oil is not going to go against gravity and leak up from the cylinder and seep into the plug threads. Any oil in the cylinder would burn off.

This is exactly what I was thinking. OP is pretty adamant that there is no oil seeping from the Valve Cover though....

[Blackhawk36]

Oil on the plug like you have can only come from a bad valve cover gasket or cracked valve cover. Oil on the coil boot causes failure and the coil must be replaced. Don't look for trouble until those two things are fixed.

[diceman]

I want to thank everyone for their comments.

After replacing the coils, plugs, o2 sensors, filters and MAF and not getting an improvement, I figured I'd bring the car to BMW before deciding to get a new engine!

BMW did a car analysis ($145) and found no error codes even after roadtesting the car and noticing a misfire. I dont know why, but they didnt get the p0303 that our scanner found over and over.

So, they manually started swapping coils and they found that the coil in cylinder 1 was not identical to the other five (I ordered 1 and then another 5) and so they swapped in a new coil and voila, the car runs perfectly.

I mentioned the compression issue and they felt a smoke test would uncover any potential leaks. I did that ($150) and it did uncover a torn INTAKE BOOT, which I had them replace. They applied half the cost of my $145 analysis to the Boot replacement, continued the smoke test and found no other issues.

Driving the car home, I found it be immensely improved (of course) but replacing all the above parts on a 165k mile car also helped greatly. Sealing off the leak returned a nice amount of power to the car.

This doesn't address my bigger issue (oil on the plug threads coming from the engine, which some of you have identified, which is either a bad valve seal or valve guides.

I do NOT get any smoke, but the car does go through some oil, probably a quart a month. I suspect the car probably needs an engine job, but probably not worth the cost on an engine with these miles.

We'll drive it for now and hope that the measly 7k miles per year we've put on it since buying it won't tax the engine that much.

Hopefully, it'll remain an oil burning machine without causing too much trouble!

I thought I'd come back and post an 'ending' since so many threads I read kind of leaves you hanging in terms of how some repair efforts faired!


Thanks again for all the input!