Plug Wires and The ECM

Discussion in 'Engine, Fuel and Exhaust' started by 90FXRS, Jul 7, 2012.

  1. 90FXRS

    90FXRS Junior Member Contributor

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    I've been wondering something off and on and it's on again so I'm asking. On a fuel injected model what happens, if anything, to the ECM program if you change wires to something that has low resistance? The wires on it are Screamin Eagle and have 4K and 1.6K ohms of resistance, this is a Softail so they're different in length. I have seen some that are 40 ohms per foot. All of this stems from wanting plug wires the same color as the sheet metal.

    Secondly, any opinions, good or bad about some of the aftermarket wires?
     
  2. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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  3. Jack Klarich

    Jack Klarich Expert Member

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    MotorCycle Series - Softail Custom Fit Ignition Wires Have a look here, I bet they can answer the Ohm question for you they have quality products:s
     
  4. R_W_B

    R_W_B Senior Member

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    40 ohms is quite a bit less than 4k, however I've never heard (yet) of plug wires causing an ION issue. I have heard of the thin electrode tip Irridium plugs and the SE plugs (also have a thin tip) causing ION problems.

    Most ION sensing circuits I've studied run off (around 80 volts) capacitance built into the secondary coil. Immediately after the plug fires the capacitance is released back across the (still burning) edge of the combustion flame.

    The edge of a flame is a conductor of sorts. The ECM compares the ION current to a "lab normal" current charateristics and makes adjustments accordingly. ION current is the same as electrical current, the term ION is merely talking in chain movement of empty electron atoms (holes) instead of electron travel.

    For some reason ( I surmise resistance differentation) the thin electrode tip plugs have issues with ION current data, causing the ECM to think it firing in a less than desirable scenario.
     
  5. HDSickness

    HDSickness Banned

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    I swithched to the SE plug wires on my 99 RK EFI about a year ago and have had zero problems can't really tell a difference from stock to be honest. They too were a bit longer than stock.
     
  6. 90FXRS

    90FXRS Junior Member Contributor

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    Well Bodeen, after that I think I learned something........I need educated. It makes sense but pretty complex.

    I've done a little research and made a couple of phone calls. From what I can gather, if the engine light comes on they're going back in the box and the other wires are going back on.

    Jack, thanks for the link. I've ran Taylor wires on other bikes and have nothing but good things to say about them. They will be getting a phone call Monday.

    I'll get back to this thread after the install and trial run on the white sled.
     
  7. R_W_B

    R_W_B Senior Member

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    Not sure if they had ion sensing in 99, I don't know what year HD introduced ION sensing, (might be in that paper Bodeen posted). All the early knock sensing in cages was done with an actual physical knock sensor mounted on the engine block. On my 88 chevy small block it's mounted into the passenger side coolant drain plug.

    But as of yet I have never heard of plug wires giving any ion issues. An extremely radical difference in ohm ratings, it would seem conceivable that they could cause problems but haven't heard of it yet.

    Some Spark Plugs on the other hand do. All of the NGK Iridiums I've seen have the narrowed electrode tip (0.06 mm). It's tapered to prevent the quenching effect. The HD SE plugs (that I've seen) also have a narrowed electrode tip. And HD's official statement on them is they are not recommended for ION sensing bikes.
     
  8. Hoople

    Hoople Account Removed

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    You also have to consider another evil which is radiated RF interference from the wires itself. That's the main reason for having so much secondary resistance to start with. I would think it's not a serious concern with early model bikes as it would be with current models. On bikes with HD Lan or serial bus, having the ECM showered with RF from a set of spark plug wires is just inviting unexplainable problems & DTC's popping up. It's open season on early model and carb bikes, but I would not use them on a 2004 and up.
     
  9. R_W_B

    R_W_B Senior Member

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    That's an excellent point Jim. When we ran wire core racing wires on our cages as teenagers, you could hear the engine whine on the radio.

    Now days they have improved the RF insulation a lot since the old days and in fact I don't believe they even still make the old carbon core plug wires anymore because of the better RF insulation (correct me if I'm wrong). In any case the ones I recently put on my truck are not carbon core and they run with no problems on the radio, and were advertised as such when I bought them. I hated those old carbon core they were so easy to break.

    But the ECM is probably more susceptable to RF than the radio since even a static discharge can fry one of those chips. Excellent point to make.
     
  10. 90FXRS

    90FXRS Junior Member Contributor

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    With the 40 ohm/foot wires on my white sled, 2001 FLSTFI, there is an issue. After installing them and running a test ride I noticed that the check engine light came on with the ignition switch......run/stop in the off position. Before the light came on with the run/stop switch. I turn the ignition on first then from stop to run. I have not checked for any codes at this time.

    Taylor sent me an email stating their wires are 350 ohm/foot. Almost 10x as much as the others and almost 10x less than the SE. Could this be a happy medium????? Not sure if I want to spend the money just to get white wires and find out they don't work.