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Discussion Starter #1
I have been off the forum for some time and am just returning due to some needed work on the old e46. I have lived in Seattle and haven't needed the car for many miles for the last five years or so. I recently moved, found a garage I could rent a lift at, and changed my oil. Now I'm deep into formulating additional maintenance that I need to do on the car.

I have been chasing this Cylinder 6 misfire for years, and it is rather intermittent, and therefore hasn't been a big issue. I had a trusted indy mechanic in Seattle recognize this and recommend changing the ignition coil. It's swapped, and still has been misfiring every so often. I changed the spark plugs around 90-100k in mileage and am approaching 140k now. I'm planning on doing the valve cover gasket, and was thinking this may be the time to swap the additional coils and spark plugs since I'll be working in this general area. I'm wondering if replacing all the ignition coils is worth it as preventative maintenance, or if I should just wait until they fail. Additionally, is it too soon to swap the spark plugs again? I don't want to throw money at parts, especially the spark plugs, if I don't need to.

I'm thinking that a vacuum leak may be the reason for my misfire, and I'll be swapping out the CCV at some point down the road and taking the manifold off entirely when I do this. I plan on using that as an opportunity to change any and all possible hoses that aren't easily reachable. I've replaced the fuel pump & fuel filter in the last 20-30k miles and was having the misfire before and after both.

Are there additional items I could swap out quickly while the valve cover is off? I'm thinking about doing the Vanos seals, but haven't fully settled on that idea yet.

Any input is appreciated.
 

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2004 330Ci 85k miles
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I only replace a coil when it fails. They can sometimes soft fail and some folks do PM replacement, your money so your call.
Spark plugs last really long, usually 100k miles, so they***8217;re probably fine.
I would remove and inspect all coils and plugs though. Always good to look for problems than them looking for you. ;)

My next steps would be to do the following and post all results in this thread so others can assist.
- Read the trouble codes
- Look at the fuel trims and MAF value at hot idle and post here.
- Do a simple smoke test. Cheap, quick, and easy. Hit the How to Smoke Test link below.
 

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What are the conditions when the cylinder misfires? The coils get 12VDC as long as the ignition is in the run or start position. The DME provides a ground. These create a very strong magnetic field within the coil. When it’s time to fire the coil the DME stops providing the ground for the coil, and the magnetic field collapses. This induces a huge voltage (50k volts) in the secondary coil, and a massive surge of electricity in the spark plug. Now, the electronic component in the DME that “turns” the ground off and on can soft fail. That is, every once in a while it’ll not “turn off” the ground, hence a misfire. I believe in the e46 DMEs that component is a metal oxide field effect transistor (MOSFET). I’d trace the wire from the cylinder 6 coil back to the DME to determine which MOSFET (if it is a MOSFET) fires the coil. Inspect it to see if there’s anything peculiar about it or the circuit board on which it sits. Additionally, find a shop that has a battery powered oscilloscope. Hook the scope’s test lead to the wire that carries the ground and go driving while someone watches the scope’s screen. Replacing the MOSFET isn’t too hard if you have some soldering skills. You can likely get a replacement MOSFET at www.mouser.com. It sells everything electronic and electrical.
 

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Skip VANOS related items, rarely a cause of misfiring. Most often when the VANOS is rebuilt/replaced so many other "maintenance" items are addressed that people falsely think the VANOS cured the problem when often it has nothing to do with the original problem.

I would first be checking Fuel Trims and performing a smoke test. The vacuum caps on the rear underside of the intake are a major problem and can cause #5 and #6 misfiring. DISA O-ring is also another major problem area.

Personally if I have the intake off, I epoxy the unused vacuum ports that are not used, no need for a vacuum cap that will deteriorate over time.

Suggest you read this thread: Solve your misfires, lean codes, rough idle - https://forum.e46fanatics.com/showthread.php?t=897616
 

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Discussion Starter #5
The VANOS seals was more due to the fact I'll have the valve cover off than for the misfire. That being said, I may just do that work in the parking garage of my building since it's a quick and easy job, especially if I'm not going to be changing the spark plugs and coils out. I'll take a look at those things while I'm in there. I've worked through some of the items in your post, jfoj, a while ago. I changed the DISA o-ring, the intake boots, cleaned the throttle body, and cleaned the idle control valve. I have a feeling that the vacuum caps may be to blame here, and will have to put together a cheap smoke kit to see if i can spot any leakage in the back end of the intake manifold.

The misfire is pretty inconsistent and has been since I bought the car 8+ years ago. When it does happen, it's usually within the first five minutes of the car being started. Either while idling a minute or two after start or when coming to a stop after driving off in the first few minutes. I don't think I've ever had the misfire pop up when the engine is warmed up. When it happens I can usually turn the car off, and on again and it's like nothing ever happened.
 
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