Misfire Problem?

Discussion in 'Discovery' started by tsutton, Jan 3, 2008.

  1. tsutton

    tsutton New Member

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    Hi,

    First post here!
    I have a 2003 Discovery with 57,000 miles. Two days ago it started running quite rough. It feels like it is mis-firing when trying to maintain a constant speed and much lower power when accelerating. The check engine light also alternates from flashing to a steady on.
    I ordered a code reader which should be delivered today.
    From what I've been able to find on this forum, I believe the first thing I should do is change the plugs and plug wires. If that seems to be the recommendation, can anyone point me to some tips for doing so? This is my only vehicle, so before beginning, I want to make sure I have whatever tools I may need on hand. Looking under the hood, it looks to be a pain in $#@!
    Thanks
    Tracy
     
  2. Disco Squared

    Disco Squared Full Access Member

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    A flashing CEL is not a good thing. It means damage to your cats is possibly occuring, so don't drive your Disco until you fix the problem. I think you are on the right track for fixing the problem, it sounds like a misfire issue.
    Tips for changing your plugs and wires:
    -Use quality parts (do a search for recommendations)
    -Keep track of the wire positions you replace, do one wire at a time.
    -Use anti-seize compound on the spark plug threads, and dielectric grease on the wire ends.
    -Be careful not to cross-thread a spark plug during installation, it's easy to do on aluminum heads.
    -Getting to the wire ends at the coil pack takes some patience; I don't know if your year truck has secondary air injection, if it does it helps to remove the air tubes first.
    -After your done, check for loose vacuum lines and such from climbing over the top of your engine.
    Good luck
     
  3. Chongo

    Chongo Full Access Member

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    one more thing

    You will want to get a plenum gasket. You'll be removing the plenum to get to the coil pack.


    best wishes Chongo.......:bandit:
     
  4. scostagl

    scostagl Member

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    I've done a wire replacement on an 04 SE without removing the plenum....it is a PITA though. Removing the plenum probably would not have made the job any faster, but it would have been easier to reach the coil packs.
     
  5. tsutton

    tsutton New Member

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    Wow what a pain that was! I didn't remove the plenum and getting to the coil packs was tough. However, after some cursing and bloody knuckles, the job is done and my Disco II is running much better than it did before the misfire problem. I also put Sea Foam in the gas as well as 2/3 of a can straight through one of the vacuum hoses. Very glad that I didn't have to spend the money or the drive and wait time to have someone else do it.
     
  6. Chongo

    Chongo Full Access Member

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    Wasted Spark system by Bosch

    Misfire Problem?

    Hi,

    First post here!
    I have a 2003 Discovery with 57,000 miles. Two days ago it started running quite rough. It feels like it is mis-firing when trying to maintain a constant speed and much lower power when accelerating. The check engine light also alternates from flashing to a steady on.
    I ordered a code reader which should be delivered today.
    From what I've been able to find on this forum, I believe the first thing I should do is change the plugs and plug wires. If that seems to be the recommendation, can anyone point me to some tips for doing so? This is my only vehicle, so before beginning, I want to make sure I have whatever tools I may need on hand. Looking under the hood, it looks to be a pain in $#@!
    Thanks
    Tracy


    Well, changing plug wires is harder than it should be, I don’t understand why LR put the coil packs between the engine and fire wall, this unit could have been placed anywhere, and worked just fine.

    Before you start, you’ll want to buy a plenum gasket, because you’ll be pulling off the plenum to get tot the coil packs. On my disco the bolts were 8 mm . The coil pack is held with 4 bolts, 8mm and 2 go straight down into the plenum adjacent to the coil pack, and the other 2 are at opposite ends of the coil pack and thread into the intake manifold.
    Before pulling off any plug wires be sure to mark their position as this system uses a “ Wasted spark system “ . The coil pack looks to have 8 individual coils when in reality there are only 4. Two cylinders share one coil. And if you put the wrong 2 together you won’t be happy with the results. I recommend removing, and replacing one wire at a time.
    Bosch’s Wasted spark system. How this works, is one cylinder is at a certain position BTDC, and when the ECM triggers an ignition coil to spark, current from the coil travels to one spark plug jumping the gap at the spark plug electrodes and igniting the air fuel mixture in the cylinder. The current then travels from the plug to the cylinder head to another plug ground, jumps the plug gap in reverse from the ground to the electrode back to the plug wire leading back to the shared coil pack of those 2 cylinders. This completes the circuit. The first cylinder was fired at a ECM timing BTDC and when firing through the shared cylinder of that coil, the 2nd cylinder will be on the exhaust stroke returning to the coil pack. Since the second cylinder that the current fires through is on the exhaust stroke and not compression the spark is termed “ Wasted “ because it did not create any ignition and no work resulted….. Wasted. This is why it is very important to get the wire back in order. This is also the primary reason for not buying gimmick spark plugs. Leave those $25.00 dollar
    Gimmick plugs
    http://www.pulstarplug.com/ on the shelf as these plugs will not work in reverse to ground shared coil systems, ( wasted spark system).

    It doesn’t matter what brand you buy, as long as the plug has the heat range that closely matches you engines requirements. If you don’t want to fool around with this Just go and buy the stock plugs for it.

    Good luck and feel free to ask any questions, we are all here to help

    Chongo
    :bandit:
     
    Last edited: Jan 10, 2008

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