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Discussion Starter #1 (Edited)
I was getting sporadic misfires, but not that bad, on the second cylinder (see http://newbeetle.org/forums/questio...ing-uphill-following-slowdown.html#post696947) . I decided that it was about the time to change spark plugs and wires. Well, I kind of did that (though with a side effect http://newbeetle.org/forums/2-0-lit...s-change-spark-plugs-yourself.html#post696366 ). But now, I'm getting completely random misfires on the 2nd cylinder out of nothing. I understand that I have a vacuum leak from the 1st cylinder fuel injector, but I have no complains about idling. AFAIK vacuum leaks are noticeable on low RPMs. I'm getting very rarely misfire on the 1st cylinder I damaged fuel injector for, but no complains.

What can be the reason for such misfires? Can it be a bad ifnition coil? Is it possible to have problem with specific cylinder with bad coil? I thought I should have multiple misfires with bad coil.

When I get enough misfires for the MIL to stay on, I have P0300, P0302, and P0304 codes. But with a scanner I can clearly see that 2nd cylinder causes all the chain (cyan color going up high on the picture).

I don't know if it is a coincidence or not, but usually when I stop engine and fiddle a bit with spark plug boot, it goes away. Sometimes it is enough shut engine and then start it again. I actually doubt there can be a bad contact between the spark plug and it's boot.

The gap I set ~0.04" on Autolite double platinum (I had some Champion before), and wires are made by Duralast (looks like the same product as was installed before). I know these are not the perfect products, but I can't believe it can be a problem.

NBM had some ideas ( http://newbeetle.org/forums/questio...ing-uphill-following-slowdown.html#post696937 ) but ... oh well.
 

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Discussion Starter #2
Well... I've been searching other threads here. All looks like I should suspect coil. I didn't notice nearby thread ( http://newbeetle.org/forums/2-0-liter-gas/47260-p0300-related-codes.html ) and this one http://newbeetle.org/forums/new-member-forum/45611-newbie-needs-help.html .

I'm a bit puzzled about different coils with either outlets in line or in a square http://newbeetle.org/forums/2-0-liter-gas/46716-rough-idle.html#post692737 . I thought they are for different engines. Are these interchangeable?
 

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Discussion Starter #4
Just swap the plug wires around on the coilpack. If the misfire moves you're found your problem.
What do you mean to "swap"? Do I have the system with the so-called wasted spark so I can swap cylinders 2 & 3 safely?
 

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Oh wait I'm totally wrong, that's the method for diagnosing bad wires / plugs, not coilpacks. I've just gotten used to working on friends' 1.8T's and we move the coils to diagnose a fried one if it's not totally obvious. I haven't had trouble with my 2.0 coil for 3 years or more so I forgot the proper way to do it and posted without thinking. Sorry!
 

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Discussion Starter #7 (Edited)
Oh wait I'm totally wrong, that's the method for diagnosing bad wires / plugs, not coilpacks. I've just gotten used to working on friends' 1.8T's and we move the coils to diagnose a fried one if it's not totally obvious. I haven't had trouble with my 2.0 coil for 3 years or more so I forgot the proper way to do it and posted without thinking. Sorry!
Are you saying it won't worth? I don't know internals of the coil pack if it supplies energy to each pair of output terminals from the same circuitry or not. If so, then perhaps I should have gotten some misfires on 3rd cylinder as well. Otherwise there is no reason to "waste" that spark if these outlets are on different circuits.

What puzzles me is that, I had rare misfires on 2nd cylinder even before I changed spark plugs and wires.

Is there a way to find out what causes a misfire? Like mixture is too lean or too reach, or there was no spark.

I'll be replacing damaged fuel injector (hopefully within a couple of weeks). I'll try to swap injectors... just in case. Though I doubt that it can be a reason.

P.S. I kept all the records from the previous owner. He changed coil-pack 3 years ago (1/14/2009 @ 74.6k miles). And 1.5 year before that (8/21/2007 @ 64.3k miles). Do they have such a short life or something else can be seriously wrong? Car has ~92k miles.
 

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Discussion Starter #9 (Edited)
Have you had the car scanned? If it is running lean the spark plug electrodes will be white. You want to see a nice golden brown colour when you pull the plugs.
I don't have enough light to take a good picture. It looks like at least some of them have a white cover. Attached picture for ~3yr old spark plugs with ~18k miles on them.

All the codes I was getting with e-bay cable & VCDS I mentioned above. They usually are like P0300, P0302, P0304, but as I said, I see misfires on 2nd cylinder with measure blocks feature.
 

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Are you saying it won't worth? I don't know internals of the coil pack if it supplies energy to each pair of output terminals from the same circuitry or not. If so, then perhaps I should have gotten some misfires on 3rd cylinder as well. Otherwise there is no reason to "waste" that spark if these outlets are on different circuits.

What puzzles me is that, I had rare misfires on 2nd cylinder even before I changed spark plugs and wires.

Is there a way to find out what causes a misfire? Like mixture is too lean or too reach, or there was no spark.

I'll be replacing damaged fuel injector (hopefully within a couple of weeks). I'll try to swap injectors... just in case. Though I doubt that it can be a reason.

P.S. I kept all the records from the previous owner. He changed coil-pack 3 years ago (1/14/2009 @ 74.6k miles). And 1.5 year before that (8/21/2007 @ 64.3k miles). Do they have such a short life or something else can be seriously wrong? Car has ~92k miles.
Did he replace all 4 coil packs before? Or just one that was misfiring?
 

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Discussion Starter #13
I've just replaced ignition coil pack. Works good so far! Though it got 3 misfires on 4th cylinder during the start:( I guess it is normal for winter weather and car not being on the go for a while. I'll do more testing, but I feel like that coil pack was the problem.

Bottom line
If your car has AZG engine and it is getting sporadic series of misfires on a single cylinder, replace your ignition coil pack. Do not attempt to swap wires as coil pack for AZG doesn't waste a spark!!!
 

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Discussion Starter #14
I thought to bump up this thread. I just replaced coils, wires, and plugs again. It has been good 6 years and about 55k miles. I wonder why it always has to break in the middle of MN winter!!!
I love AutoZone's lifetime warranty!
 

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Warning: The last time I tried to use Autozone's "lifetime warranty" they tried to deny it.

Long story, but I'll try to shorten it. They said that they only allow one replacement under that warranty. The first time I had them replace the alternator under warranty was because it failed in a month. The replacement failed within a year and they said it wasn't covered because I already had it replaced once under warranty. I argued with the store manager for quite some time (having worked previously in retail, I knew I had a good chance to get a replacement if I kept arguing with them). In the end, the manager relented and said they'd do it for me "just this one time", but any other future replacements under "lifetime warranty" were only good for ONE replacement only. I didn't feel bad about doing this since I paid extra for the "lifetime warranty" part and it should have lasted at least a year.

This was in my 1991 Ford Crown Victora. The next time the alternator failed (after maybe another year), I replaced the original first generation 65 amp alternator with a third generation 130 amp alternator from a junkyard that was nice and shiny, even though it was in a junked car. This required a bit of rewiring, but there are "how to" instructions for this all over the Internet since this is a common upgrade to do in an old Ford. The new alternator fixed my headlight dimming problems and lasted until I junked the car last summer. Still miss that big old Box.
 
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