Misfire Diagnosis

[C130Driver]

I have a 2000 E46 with about 175K that has recently developed a misfire problem which has me boggled and any help or ideas would be greatly appreciated.

Earlier this summer the car developed a misfire issue which I positively determined to be a failed coil. I replaced only the one coil - because you know, there's a reason I drive a 2000 BMW and not a 2017 BMW - and the problem was solved. So, you can understand why, when it developed a new misfire about a month ago, the first thing I thought of was one or some of the other coils were on their way out. I ran the CEL and determined only 2 cylinders - different than the one whose coil was originally replaced - were misfiring. Knowing I should have replaced all 6 coils anyway, I went ahead and bought two more and replaced them. I thought, for about a day this fixed the problem, until it came back. I ran the CEL, and this time it was two different cylinders. I bit the bullet and replaced the remaining three cylinders' coils. The problem still presented itself. All six cylinders are misfiring. I truly believe it was just coincidence that "new" cylinders were throwing the CEL light each time, and in fact they were not the source of the problem with the exception of the first one this past summer.

When pulling the last 3 coils I noticed a substantial amount of oil on the coil boots. I replaced the valve cover gaskets within the last year, so I thought maybe it had failed, causing a vacuum leak. I went ahead and replaced it again under warranty. It was still misfiring.

Just to play it safe, and because they were coming due anyway, I replaced the spark plugs. No change

All of this was within a few days' time period. I then began to notice a low whistle coming from the intake area. I replaced the intake boot within the last 2 years and the new one is still very pliable so I began to suspect the DISA. I pulled the DISA and sure enough the O-Ring had failed. It had a giant tear. I replaced the O-Ring and the whistle went away. The misfires seem less severe, but still occur. Also, while I had the DISA off I was able to determine the seals in it were no good, so I went ahead and replaced it too.

So basically, this is where I'm at. Here is some additional info I've been able to gather while trying to trouble shoot. When I first start the car, it is fine, no misfire. Typically, it begins to present itself at idle, but once it starts it continues to misfire. If I shut off the car and restart it, the misfire goes away until it later presents itself at idle again. This had me thinking it might be electronic, specifically the MAF Sensor. I cleaned it with MAF cleaner. Also, to trouble shoot it, I've read if you unplug while the engine is running and the misfire goes away or improves this could be a sign of a failing sensor. My misfire definitely gets worse if the MAF is unplugged. So I think I've ruled that out, thoughts? Also, I was thinking maybe the Idle Control Valve, since it begins to misfire while idling. But, if it's the ICV, does it continue to misfire when driving or only while at idle? Also, I had the intake off the replace the water pipe at about 150K and thoroughly cleaned the ICV then. 25K miles doesn't seem like enough to foul it up. For what it's worth, I don't claim to have replaced all the vacuum lines, but while I had the intake off I tried to inspect and replace all the vacuum lines I could find. Thoughts on the ICV? Thoughts in general? Thanks in advance.

[Pelican Parts]

Have you checked the cylinder compression?


-Dmitry

[ryanr1299]

Are you getting any other codes besides cylinder misfires?

[MIKYZZ4]

What tool are you using to obtain codes, and can it clear the codes?
I highly suspect intake leaks as the cause of your multiple misfires.
Your going to have to obtain the services of a competent shop,
that can perform a professional smoke test, using a pro smoke machine.
A test of the intake, CCV, and fuel tank ventilation systems, will provide confirmation of hard to find leaks.

[johnjmurray]

C130: You should try clearing the ECU adaption codes. The poor-mans method is to disconnect the battery for about an hour. When you get the battery reconnected, don't just start the car. Turn the key to pos 2 for about 20-30 seconds. Then to Off for another 20-30 seconds, then fire it up.

[C130Driver]

Hey all. Thanks for the replies.

1. I haven't checked the cylinder compression nor do I have the tools to do so.

2. I do get other codes, I've forgotten what they are off the top of my head and am not at home. I can check and report back. I believe fuel mis trim. I know the fuel purge valve code is given, but I've had that for the last 60,000 miles without issue.

3. I've been using an inexpensive OBD II code reader. It will clear them. I would MAYBE consider having a shop do diagnosis but if it gets to the point of having them do repairs I'll probably just replace the car. It's only worth a few thousand. No sense of investing 100% of its value into repairs when it's approaching the end of its life anyway. You think the above mentioned fuel vent issue is a possible causes? Like I said it's been on for years without issue.

4. Thanks I'll try this and report back.

[legoman67]

fuel vent faults wont cause misfires.

[MIKYZZ4]

What tool are you using to obtain codes, and can it clear the codes?
I highly suspect intake leaks as the cause of your multiple misfires.
Your going to have to obtain the services of a competent shop,
that can perform a professional smoke test, using a pro smoke machine.
A test of the intake, CCV, and fuel tank ventilation systems, will provide confirmation of hard to find leaks.

Fuel trim issues combined with multiple cylinder misfires, points to an intake leak.DO THE TEST.
The only reliable way to confirm that you have found all leaks, is the smoke test(~$100)
The oily coil boots are concerning, considering you have replaced the valve cover gaskets twice,
in a short amount of time, as oil filled spark plug tunnels can definitely cause misfires.
If the gaskets were installed correctly, then I highly suspect a possibly cracked valve cover.

[C130Driver]

Thank you for the continued replies. Just yesterday I noticed the engine has developed a whistle coming from the intake area; though I'm having trouble determining if it's coming from the intake or the valve cover. So I'm thinking I'll pull a few coils and check for oil again. If there's no oil that should indicate the previous oil was in fact from a failed gasket, and I'll suspect the intake. If there is oil, that should point towards a cracked valve cover. Thoughts?

[MIKYZZ4]

Check for a cracked CCV hose traveling parallel to the coils, possibly causing the unknown whistling intake leak and oil.

[C130Driver]

Are you talking about the steel line that runs along the fuel log?

[C130Driver]

Well, half steel half rubber...

[MIKYZZ4]

Make sure no oil is filling the sparkplug tunnels.
Who is replacing the valve cover gaskets, you personally, or a shop mechanic?
You are replacing with a Genuine BMW gasket set, not RTV sealant, correct?
New sets of these were installed, correct?:
Don't skimp , quality counts.

[C130Driver]

Sorry for the long delay. I've been really busy at work which requires me to travel a lot and I haven't had time to further diagnose the car until last night. The whistle that I mentioned before that is coming from the intake area was short lived and went away for a while. Then it began to come and go, I noticed it seemed to come back when it rained outside and would often go away when it was dry out. Since then it has come back to stay. However, it isn't a constant whistle, it only does it when the engine is going from a higher RPM to a lower one. For instance, when the RPMs drop while I'm shifting gears, or if the throttle is at idle but the RPMs are higher and decelerating due to coasting with the car in a gear rather than neutral. This leads me to believe the whistle is coming from the intake rather than the valve cover gasket.

I removed the valve cover again and inspected the gasket and cover itself. Both seem to be in like new condition. I removed all 6 coils and inspected the wells for oil. Numbers 3-6 were bone dry and numbers 1 & 2 and a very very slight amount of oil which I believe to be residual from the previous leak. There was no pooling of oil, only a few drops worth in the very bottom. To answer questions, I am not using RTV, but I am also not using genuine BMW gaskets. Instead I'm using a generic. I forget which brand I used. Also, I am the one doing the work. When I replaced the gasket, yes I replaced all three portions. Around the rim of the valve cover as wells as around spark plugs.

Diagnosis aside, I was thinking further about the valve cover gasket, and I was wondering how sure you are that area is under vacuum. When I first purchased the car it had a valve cover leak and was leaking massive amounts of oil onto the exhaust manifold. It has obviously since been repaired, but even then it ran fine. No misfire, no hesitation. Versus now, it runs like crap and there is no oil leak. No smoke like before. Just a thought.

At this point, I'm thinking it must be the intake gasket. Which I am dreading because I know it is a lot of work to access what is otherwise a simple fix. As always thanks for all the help and insight and I'll report back. Thoughts?

[MIKYZZ4]

Are you talking about the steel line that runs along the fuel log?

[C130Driver]

Well I finally finished removing the intake manifold and I think it's safe to say my problems were due to a failed gasket. What I can't help but wonder is what would cause a complete failure like this when the gasket was changed January 2016.
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[MIKYZZ4]

Was it an OE or OEM replacement?
Cheap aftermarket imitation replacement parts, are common early failure items.