Misfire..........help (Plugs and wires)

[paul540/m3]

I'm having some problems with my car, the check engine light is coming on and when scanned the code reades misfire in cylinder 2. My mechanic switched plug one and 2 and the light went away for a bit but then when it came back on a couple days later it read misfire in cylinder 1 and 2. The light seams to come on when I take the car to high revs like 4k plus. I'm thinking I need to change my plugs and wires. I guess it's about time, 70k km right? Anyways my question is what is available in terms of plugs and wires for this car? Are there any aftermarket upgrades I should be aware of or just stick with OEM? Any disadvantages with aftermarket products?

Thanks in advance.

[thejlevie]

Did he swap the coil or the plug? And did he clear the fault codes after the swap?

If the fault codes weren't cleared after the swap you'll see the previous fault as still present. And that would mean that whatever he swapped to cylinder 1 is the cause of the misfire and should be replaced.

Your car doesn't have plug wires, instead it has an ignition coil for each cylinder. It isn't uncommon to have an ignition coil go bad and cause misfires. Probably more common is for the valve cover gaskets to leak oil into the plug wells and cause misfires. Only rarely, in my experience, is a plug at fault unless the car has a huge amount of mileage on a set of plugs (something over 150k). However, plugs should be replaced on general principles by 100k.

[paul540/m3]

Fault codes were cleared after the first time, and I beleive he swaped the plug not the coil. What action do you suggest I take from here? Should I change the plugs just to be safe? If so which plugs should I use? How big of a job is the valve cover gasket?

Also if i'm changing the plugs should I also change the coils? How much should plugs and coils cost me? Just the parts.

BTW thanks so much for the quick response and your help

[thejlevie]

If he swapped the plug and cleared the fault codes, it sounds like you might have a bad plug (now in #1) and a bad coil on #2. Coils are pricey, around $90 each, so one only wants to replace a failed one. Plugs run close to $16 each at a dealer. I don't find replacing valve cover gasket to be that big of a job. A bit tedious because of the stuff that has to come off as a part of the job, but not real difficult.

It would be a help to know how many miles are on the car and what its production date is.

[paul540/m3]

The car has 70,000 KM on it and production date is 11/97.

Ok so, I'll scan the car again and see what codes pop up, and then see what my mechanic says. But I beleive you are correct with the faulty coil in cylinder 2 and plug in cylinder 1. Would it be beneficial to do all the plugs at once?

I also saw on Bavauto that they have high performance coils? Whats the difference and are they worth doing? I ideally want to replace just the single coil if I can get away with it, but if need be should I go high performance coils?

[thejlevie]

At 70km it is something of a toss up as to whether to replace all of the plugs. They should have a bit more life in them, but they they are pretty inexpensive and it would be a good opportunity to check all of the plug wells for oil. Leaking valvecover gaskets on a 540 at 70km and 8 years of age is a real possibility.

In my opinion the ignition coils in the car now are more than good enough. Hot coils might be desirable on a car with a supercharger, cams, etc. But I don't believe they provide any real benefit to a stock engine. I tend to view those like I do CAI's... As automotive snake oil.

[paul540/m3]

LOL ok so stock coils it is

I'll make sure my mechanic takes a look at the plug wells as well to make sure a new valvecover gasket isn't needed.

Thanks again for your help it is greatly appreciated.