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Thread: Wet weather misfires

  1. #1
    One of those purists you keep hearing about. sdg3205's Avatar
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    Wet weather misfires

    Recently I've experienced a misfire when driving in the rain. It's a pain in the ass on flat roads, but we're doing a rally in May up in the mountains and I'll need all 6 cylinders to be on their best behaviour.

    I spoke with toby and he has some good insights. One possibility is the blast resistor is getting wet and causing voltage drop at the coil, another is that water is finding its way into the distributor. Yet another possibility is my wires are toast, but they were new Bosch from DMC in 2010 and have only about 15k miles on them.

    The really bizarre thing is that this has only begun recently, which would actually lead me to believe it's due to "wear and tear." Has anyone else experienced this sudden wet-weather misfire?
    Dave

    Here, somewhere.


  2. #2
    Ramblin' Wreck from Georgia Tech RamblinDMC's Avatar
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    I had a similar problem and found out that my distributor cap had cracked in half!

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  3. #3
    One of those purists you keep hearing about. sdg3205's Avatar
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    Quote Originally Posted by RamblinDMC View Post
    I had a similar problem and found out that my distributor cap had cracked in half!

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    Damn! so with the crack it was fine when dry, but misfired when wet?
    Dave

    Here, somewhere.


  4. #4
    Ramblin' Wreck from Georgia Tech RamblinDMC's Avatar
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    It misfired sometimes when dry, but became even worse when wet.

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  5. #5
    Senior Member Bitsyncmaster's Avatar
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    Condensation inside the cap is one cause of sudden misfire problems. It may or may not be worse in the rain.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  6. #6
    Junior Member cis6409's Avatar
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    Location:  ireland

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    Mine was the same , driving in the wet was a pig it got so bad I had to pull over , eventually took it off the motorway and got on to secondary road . Nursed her back home but thankfully the rain stopped and the roads dried off considerably and it was like a switch going off , as soon as it got to dry off power was restored and she flew home ..

    Changed the plug leads cause found 3 of them with tiny cracks and tears from vibration rubbing off the manifold(5 years old or so ) .
    Also replaced distributor cap and rotor and found the cap had a crack on one side and was letting water In , you could see the black scorch track down the inside of the cap where it was arcing affecting 2 of the 6 points but only in that area ..

    Since then all good in the rain thankfully

    Cheers
    Shane
    Last edited by cis6409; 04-07-2017 at 10:04 AM.
    only from the past can we choose the correct path for the future...

  7. #7
    Delorean Guru
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    Quote Originally Posted by Bitsyncmaster View Post
    Condensation inside the cap is one cause of sudden misfire problems. It may or may not be worse in the rain.
    Doubtful it is the ballast resistor but it could be bad/dirty/rusty connections to it. Remove each wire one-at-a-time and clean up any rust. It is most likely a problem in your secondary ignition system and that means replacing the dist cap, rotor, and ignition wires. If the spark plugs haven't been done in a while, them too. The wires could have been damaged and that is causing the problem. When installing them you must be careful not to bend or pull on them. Rare for a cap to crack but if mishandled or not fit to the dist properly it can happen.
    David Teitelbaum

  8. #8
    TGTF (Too Greek to Function) AugustneverEnds's Avatar
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    I experienced a misfire several times this past summer in wet weather. This winter it struck again when the car was parked in the garage. I needed to take the intake off for another issue and that's when I noticed the Bosch wires (installed in 2013) were slipping badly off the distributor cap. I did buy the Bougicords I posted about in another thread (cross referenced with a Volvo 262) and they fit fine especially over the spark plug well, very snug. I still need to put my intake back on so I haven't fired it up yet with the new wires. I will let you know how it goes.

    I personally think Bosch's wires are a mediocre product and will only last 3 or 4 years when the car is being driven on a fairly regular basis.
    Nick A.
    Νικος Αυγουστινατου

    1988 BMW 325iS
    1982 DeLorean DMC-12

  9. #9
    Senior Member DMC5180's Avatar
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    I had an issue with arc jumping on my Original Coil. I replaced the coil and the coil wire. The coil wire was the original one with EMI shielding. The replacement wire is not shielded. I often wondered If that 30 year old wire was also a contributing factor. If the rubber insulation deteriorated on the lead it would be a very short jump for an arc to reach the Shield ground.


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  10. #10
    Senior Member Josh's Avatar
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    Although I do not have the prv, I had a misfire under similar conditions. Turns out it was a damaged plug wire.
    It seems hard to find a nice quality plug wire. Ive had multiple instances there the wire just falls apart, slides off the crimped terminal. Worse yet it partial slides off the crimped terminal and you are none the wiser that there is a poor connection.

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