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  1. #1
    Registered Member One Ring
    Join Date
    Feb 12 2012
    AZ Member #
    88105
    Location
    Stroudsurg, PA

    Misfiring, now won't start. Plugs, coils?

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    Hello,

    I don't have a code reader, but my check engine light came on, and I'm 99% sure my A4 started misfiring (shaky, underpowered acceleration) pretty bad. I got her home, opened the hood, and pulled the coils to inspect them for any obvious damage/wear. Nothing obvious, but when I put them back in, the car wouldn't start at all.

    Also, I'm not sure if this happened when I pulled the coils, or what but the wire connecting one of them to the block broke. Here's a picture:


    (Yes, I found a mouse nest under my engine cover. Thought maybe he chewed something, but no evidence of that. He couldn't have been there for very long, I drive every day, and had just had teh cover off a few days earlier)

    Can someone tell me what this is? Looks like a ground-type thing to me, but I'm not that car-savvy. Is this preventing the engine from starting?

    How can I check my coils/plugs and determine what I need and how many? Any suggestions as to cheap(er)/good ones?

    Thanks!

  2. #2
    Senior Member Three Rings
    Join Date
    Mar 20 2009
    AZ Member #
    40142
    Location
    Scotland

    What color is the broken wire?

    If its brown, its the earth for the coils...

  3. #3
    Veteran Member Four Rings walky_talky20's Avatar
    Join Date
    Jun 30 2008
    AZ Member #
    30427
    Location
    Erie, Pennsylvania

    The little black jobber is the filter cap for the coils. Cuts down on radio interference and such. Most 1.8T's don't have them (is yours a 2001.5?). I would recommend you just tape that wire up and leave it be.

    In any case, I'm pretty certain you blew fuse #29. Check it.
    ^Don't listen to this guy, he's not even a mechanic.
    2001 Laser Red A4 1.8TQM, 5-Speed Swapped, APR 93, Splitter, electronic oil pressure gauge, B6 Sport 17's, ST Coilovers,
    Need to borrow a Cam Chain Tensioner Tool? $4 for shipping. PM me. *available*

  4. #4
    Registered Member One Ring
    Join Date
    Feb 12 2012
    AZ Member #
    88105
    Location
    Stroudsurg, PA

    Quote Originally Posted by walky_talky20 View Post
    The little black jobber is the filter cap for the coils. Cuts down on radio interference and such. Most 1.8T's don't have them (is yours a 2001.5?). I would recommend you just tape that wire up and leave it be.

    In any case, I'm pretty certain you blew fuse #29. Check it.
    That was it. Replaced it and it started right up. Misfiring stopped too. I guess it was a loose connection and fiddling with it fixed that?

    If you don't mind briefly explaining, how did you know I'd blown a fuse, and how did you know which one (as there were several with the same label)?

    Thanks so much. I don't have to hitch a ride to work tomorrow!

  5. #5
    Registered Member One Ring
    Join Date
    Feb 12 2012
    AZ Member #
    88105
    Location
    Stroudsurg, PA

    Also, I'm fairly certain its not a 2001.5, just straight 2001.

  6. #6
    Veteran Member Four Rings walky_talky20's Avatar
    Join Date
    Jun 30 2008
    AZ Member #
    30427
    Location
    Erie, Pennsylvania

    Quote Originally Posted by dg988 View Post
    If you don't mind briefly explaining, how did you know I'd blown a fuse, and how did you know which one (as there were several with the same label)?
    Because I'm awesome like that. (lol)

    Real Answer: I think your misfiring was legit and it may come back. Could have been a loose connector or coil pack that wasn't seated quite right, I've had that before. In any case, due to the age of your car, and the fact that you did a lot of moving of the [often crispy] coil pack harness, my money was on an intermittent short in the coil pack harness.

    In any case, there is one particular fuse (#29) that provides power to only the coil packs. Shorts in the coil pack harness (intermittent or otherwise) will blow this fuse but produce no other symptoms. It is somewhat common for this to happen because our little turbo's like to bake the harness. Then a chap goes to unplug stuff and move it and it pops the fuse. It is entirely possible that the wires are in bad shape and your original misfiring issue was a broken wire in the harness that was merely "open", so 1 coil wouldn't fire. Then you moved it a bit and it went from "open" to "dead short to ground" and blew the fuse. If that is the case, it is quite possible that these problems will reoccur. Generally speaking, fuses don't just fail of their own accord. Something caused it. In this case, either a bad coil pack (rare) or a short in the harness (not as rare). Cheapest way to repair is to use the OEM Jetta 1.8T repair harness:
    http://www.ecstuning.com/Search/Coil...arness/ES7679/

    Practically speaking, if your car is running fine now, you don't have to do anything. But just be aware that it may fail again at any moment. At least a cursory inspection of the harness is recommended. Looking behind the jacket for this type of stuff:
    ^Don't listen to this guy, he's not even a mechanic.
    2001 Laser Red A4 1.8TQM, 5-Speed Swapped, APR 93, Splitter, electronic oil pressure gauge, B6 Sport 17's, ST Coilovers,
    Need to borrow a Cam Chain Tensioner Tool? $4 for shipping. PM me. *available*



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