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Cyl 4 misfire - discolored ignition wire? 850 1996

posted by  jjmcc on  Sun Jan 13 11:08 CST 2008
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last visit: Sat Jul 9 12:19 CST 2011
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My 96 850 with 143K miles has been running roughly intermittently - seems to be correlated with not driving it for several days. Sometimes the engine runs very smooth, when well-warmed up for example, sometimes it's jerky and rough.

A couple of weeks ago it threw a P0304 code - misfire in cylinder #4. I inspected the plugs and wires, and all seemed OK, except the #4 wire was brownish in the long straight region between the plug and the seal. All the other wires were light gray. I reset the code and drove for a while, then it threw the same code, same cylinder again today.

I'm thinking about replacing the wires, cap and rotor, which have ~80K on them. That should overkill this problem, I hope. In the meantime, does anyone have any thoughts about whether this brownish #4 wire is really the cause of the roughness, and if so, whether it points to other issues?

Thanks








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    Cyl 4 misfire - discolored ignition wire? 850 1996

    posted by  james_a_sousa on  Sun Jan 13 14:56 CST 2008
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    last visit: Thu Oct 23 18:51 CST 2014
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    Why not buy a set of wires and change just that one? Don't change anything else.

    Tuning your car is good for it, but changing just that wire will answer your question.

    The symptoms you describe could be explained if the wire was porous and absorbs some moisture during the sitting periods, baking it off when you drive the car.
    --
    '96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 435,000 miles put on 9 bricks








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    Cyl 4 misfire - discolored ignition wire? 850 1996

    posted by  Rule 308 on  Sun Jan 13 14:42 CST 2008
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    last visit: Tue May 8 09:20 CST 2012
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    While it could be a faulty injector it is probably in your secondary ignition system. Hanging new cap, rotor, and wires sounds like a good idea but I would not stop there, stuff in a new set of factory plugs while you are at it. Use Bosch cap and rotor, Bougicord wire set, and factory Volvo plugs. The brown section of the #4 wire may be indicative of a bad wire but I have not run into that on an 850 yet. What I do see is failure of these components in the 100-120K area and I have not noticed any brown discoloration of the wires, usually it is in the cap and rotor area that you find debris and discoloration.
    Every now and then you find a new one though, I had one come in with the bolt that secures the base for ignition rotor to the back of the cam shaft broken off. Funny thing is the car drove in on it's power with a bit of a miss under load and no misfire codes. I had to drill out broken bolt, replace all of the worn out stuff and everything was good after that.

    Mark







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