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Thread: Lighted Plug cap question

  1. #1
    Senior Member DonTom's Avatar
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    Lighted Plug cap question

    I am very curious why they say these cannot be used with fuel injected motorcycles. What does fuel injection have to do with these spark plug caps????

    Does anybody have a guess?

    I bet they would work fine with EFI. Why wouldn't they?

    BTW, I use them on my 1971 BMW R75/5 and I am going to put them on my 1984 Venture.

    I discovered that on my 1984 1200 CC four cylinder Venture, I cannot even tell the difference when it's running on three cylinders if on level ground.

    These tell me, at least, that all four cylinders have spark.

    None of my motorcycles have fuel injection, so I am only curious about this fuel injection limitation because I cannot make any sense of it.

    They say these caps do not effect spark in any way. So what is so special about fuel injection when these lighted caps are used?

    -Don- SSF, CA

  2. #2
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    My guess is that they do drain off a little of the spark, and the fuel-injected bikes are more sensitive to this.

    My other guess is that a fuel-injected bike has tighter emissions requirements, and these might cause the bike to fail.

    Chip H.

  3. #3
    Vulture of The Western World Eric's Avatar
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    I agree with Chip's guess.

    My understanding is that EFI systems are very sensitive to voltage spikes/drops (a non-issue with carburetors) and there may be some potential issue with that which is why, I suspect, the manufacturer says don't use 'em with EFI. Their lawyers probably advised them to do so based on the possibility the government or some lawyer might try to go after them....


    Quote Originally Posted by DonTom View Post
    I am very curious why they say these cannot be used with fuel injected motorcycles. What does fuel injection have to do with these spark plug caps????

    Does anybody have a guess?

    I bet they would work fine with EFI. Why wouldn't they?

    BTW, I use them on my 1971 BMW R75/5 and I am going to put them on my 1984 Venture.

    I discovered that on my 1984 1200 CC four cylinder Venture, I cannot even tell the difference when it's running on three cylinders if on level ground.

    These tell me, at least, that all four cylinders have spark.

    None of my motorcycles have fuel injection, so I am only curious about this fuel injection limitation because I cannot make any sense of it.

    They say these caps do not effect spark in any way. So what is so special about fuel injection when these lighted caps are used?

    -Don- SSF, CA

  4. #4
    Administrator Ken's Avatar
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    Quote Originally Posted by DonTom View Post
    I am very curious why they say these cannot be used with fuel injected motorcycles. What does fuel injection have to do with these spark plug caps????

    Does anybody have a guess?

    I bet they would work fine with EFI. Why wouldn't they?

    BTW, I use them on my 1971 BMW R75/5 and I am going to put them on my 1984 Venture.

    I discovered that on my 1984 1200 CC four cylinder Venture, I cannot even tell the difference when it's running on three cylinders if on level ground.

    These tell me, at least, that all four cylinders have spark.

    None of my motorcycles have fuel injection, so I am only curious about this fuel injection limitation because I cannot make any sense of it.

    They say these caps do not effect spark in any way. So what is so special about fuel injection when these lighted caps are used?

    -Don- SSF, CA
    This is purely guesswork, Don. The ignition and fuel injection characteristics are closey matched on EFI engines. My guess is that the effect of the 'Lighting' plug cap would alter the load parameters on the Electronic part of the EFI. If this were the case then the resultant spark would probably not be matched to the amount of injected fuel and a poor burn could result. I think the 'Lighting' cap (which may embody a spark gap) could have the same effect as badly gapped plugs, or an incorrectly set-up fuel injection system.

    Just my guess.

    Ken.
    Last edited by Ken; 07-01-2011 at 10:32 AM.
    Die dulci fruimini!
    Ken.
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  5. #5
    If they are claiming that it doesn't alter the spark in any way my guess is that they are using some sort of inductive charging system to provide the power. Filling and draining the capacitor quickly will generate a radio frequency which I suppose could interfere with fuel injection systems depending on how strong the signal is.

    For instance, if you are at 8K rpm (in theory) you would generate a 2Khz radio signal with each of those plugs. That's the coil and plug wires for cars are now electronically shielded.

  6. #6
    Administrator Ken's Avatar
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    Quote Originally Posted by Steve View Post
    If they are claiming that it doesn't alter the spark in any way my guess is that they are using some sort of inductive charging system to provide the power. Filling and draining the capacitor quickly will generate a radio frequency which I suppose could interfere with fuel injection systems depending on how strong the signal is.

    For instance, if you are at 8K rpm (in theory) you would generate a 2Khz radio signal with each of those plugs. That's the coil and plug wires for cars are now electronically shielded.
    It is a fact that, on EFI Harleys, the neon lights can cause the 'Engine' warning light to show. This is because the computer senses that the resistance of the ignition leads is outside the normal parameters. (From a Harley website)

    Ken.
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    Ken.
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    Senior Member DonTom's Avatar
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    Quote Originally Posted by chiph View Post
    My guess is that they do drain off a little of the spark, and the fuel-injected bikes are more sensitive to this.

    My other guess is that a fuel-injected bike has tighter emissions requirements, and these might cause the bike to fail.

    Chip H.
    My guess is they will still work perfectly on EFI. I see no logical reason why they won't. But I think the best guess is emissions, but I even doubt that.

    I would be very surprised if anybody would notice any difference in any way with these added to a fuel injected engine's plugs.


    After all, it's possible for a fuel injected engine to have the exact same ignition system as having a carburetor. Heck, you can have fuel injection even with old fashioned points and condenser. How the fuel is injected doesn't necessarily say anything about the ignition system.


    -Don-

  8. #8
    Senior Member DonTom's Avatar
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    Quote Originally Posted by Ken View Post
    It is a fact that, on EFI Harleys, the neon lights can cause the 'Engine' warning light to show. This is because the computer senses that the resistance of the ignition leads is outside the normal parameters. (From a Harley website)

    Ken.
    Somehow I missed your message.

    IMO, that makes perfect sense! The problem is NOT the EFI, but what the sensors look for often in such, at least these days with OBD2 & etc.

    -Don-

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    Yep. The computer is able to detect misfires and after a few will set a code.

    Changing the resistance in the wiring & plug "system" will make the computer think something has gone wrong.

    Chip H.

  10. #10
    Senior Member grouch's Avatar
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    I worked on an early MPFI engine after they got away from CFI type injection. The guy had bought some cheap plug wires. At night you cold actually see the phantom glow on the wires from the voltage discharge. This created RFI that freaked the computer out. A better shielded plug wire set cleared it up in no time. It was a littl creepy watching these eerie lights moving around under the hood.
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  11. #11
    Senior Member DonTom's Avatar
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    Quote Originally Posted by chiph View Post
    Yep. The computer is able to detect misfires and after a few will set a code.

    Changing the resistance in the wiring & plug "system" will make the computer think something has gone wrong.

    Chip H.
    It must do that by noticing somehow that the high voltages goes up on the secondary ignition. I don't see how the resistance can be checked there during normal operation.

    -Don-

  12. #12
    Senior Member DonTom's Avatar
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    Quote Originally Posted by chiph View Post
    Yep. The computer is able to detect misfires and after a few will set a code.

    Changing the resistance in the wiring & plug "system" will make the computer think something has gone wrong.

    Chip H.
    How do they detect the resistance of the wires with spark plugs in series? The only way I can think of is if the secondary ignition voltage is slightly higher at the coil from the reduced load of having the lighted cap in series with the spark plug. And I would expect that voltage difference to be so slight that it could not reliably be detected.

    -Don-

  13. #13
    Administrator Ken's Avatar
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    Quote Originally Posted by DonTom View Post
    How do they detect the resistance of the wires with spark plugs in series? The only way I can think of is if the secondary ignition voltage is slightly higher at the coil from the reduced load of having the lighted cap in series with the spark plug. And I would expect that voltage difference to be so slight that it could not reliably be detected.

    -Don-
    Could be a couple of thousand volts, Don. Also, the effect of the (neon?) gas striking could put some funny shapes into the ignition waveform. Computers can detect changes of minute fractions of volts with no problem. A change in averaged ignition voltage should be easy peasy.

    Ken.
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    Ken.
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  14. #14
    Senior Member DonTom's Avatar
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    Quote Originally Posted by Ken View Post
    Could be a couple of thousand volts, Don. Also, the effect of the (neon?) gas striking could put some funny shapes into the ignition waveform. Computers can detect changes of minute fractions of volts with no problem. A change in averaged ignition voltage should be easy peasy.

    Ken.
    I doubt if they would cause a change of a couple of thousand volts. That could be around 20% of the voltage to the plugs, which would be enough to reduce performance even without EFI.

    But the rest of your post I can agree with. After all, I know they DO detect misfires somehow.

    -Don-

  15. #15
    Administrator Ken's Avatar
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    Quote Originally Posted by DonTom View Post
    I doubt if they would cause a change of a couple of thousand volts. That could be around 20% of the voltage to the plugs, which would be enough to reduce performance even without EFI.

    But the rest of your post I can agree with. After all, I know they DO detect misfires somehow.

    -Don-
    My information is that typical Electronic Ignition outputs are in the order of 30 to 40KV and some of the CDI systems go up to 60KV. If I am right then assuming the neon breakdown voltage to be equivalent to a 1 to 2mm spark gap then a 3 to 6 KV variation would not be out of order.

    Air breaks down at around 30KV per cm. If the neon light approximates to a 1 mm spark gap then we are looking at a 3KV variation. Assuming that the plug gap is 0.5mm then the remaining 27 KV would still easily jump the spark gap even taking the increased pressure within the cylinder into consideration. I still think that the variation in (apparent) ignition circuit resistance would be easily detectable by modern computer electronics.

    Ken.
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    Ken.
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  16. #16
    Senior Member DonTom's Avatar
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    Quote Originally Posted by Ken View Post
    My information is that typical Electronic Ignition outputs are in the order of 30 to 40KV and some of the CDI systems go up to 60KV. If I am right then assuming the neon breakdown voltage to be equivalent to a 1 to 2mm spark gap then a 3 to 6 KV variation would not be out of order.

    Air breaks down at around 30KV per cm. If the neon light approximates to a 1 mm spark gap then we are looking at a 3KV variation. Assuming that the plug gap is 0.5mm then the remaining 27 KV would still easily jump the spark gap even taking the increased pressure within the cylinder into consideration. I still think that the variation in (apparent) ignition circuit resistance would be easily detectable by modern computer electronics.

    Ken.
    If you take a close look inside of a flashing cap, you will see it's just a neon lamp in a colored shell. It looks like a NE-2, which requires around 90 volts for it to get to maximum brightness. So there's probably even less than a 100 volt drop across these neon lamps when they are in series with the ignition wires. That's why they have no effect on the plugs. Seems it would even be too small of a change for even for EFI, at least in most cases.

    BTW, I made an experiment with a ignition spark length tester. The length of the spark did not change at all between the stock zero ohm caps and the lighted infinite ohm caps in series.

    -Don- SF, CA

  17. #17
    Administrator Ken's Avatar
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    Quote Originally Posted by DonTom View Post
    If you take a close look inside of a flashing cap, you will see it's just a neon lamp in a colored shell. It looks like a NE-2, which requires around 90 volts for it to get to maximum brightness. So there's probably even less than a 100 volt drop across these neon lamps when they are in series with the ignition wires. That's why they have no effect on the plugs. Seems it would even be too small of a change for even for EFI, at least in most cases.

    BTW, I made an experiment with a ignition spark length tester. The length of the spark did not change at all between the stock zero ohm caps and the lighted infinite ohm caps in series.

    -Don- SF, CA
    In that case, Don, I haven't a clue why they say 'Do not use with EFI.'. I shall try and find out a bit more when I have some spare time.

    Ken.
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  18. #18
    Senior Member DonTom's Avatar
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    Quote Originally Posted by Ken View Post
    In that case, Don, I haven't a clue why they say 'Do not use with EFI.'. I shall try and find out a bit more when I have some spare time.

    Ken.
    Well, if you do, please let me know. I cannot make any real sense out of it.

    -Don-

  19. #19
    Administrator Ken's Avatar
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    Quote Originally Posted by DonTom View Post
    Well, if you do, please let me know. I cannot make any real sense out of it.

    -Don-
    Will do, Don. My next thought was that there could be quite a high value resistor in series with the neon. BUT! - in the meantime, I have contacted the supplier for further information.

    Ken.
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  20. #20
    Administrator Ken's Avatar
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    Quote Originally Posted by Ken View Post
    Will do, Don. My next thought was that there could be quite a high value resistor in series with the neon. BUT! - in the meantime, I have contacted the supplier for further information.

    Ken.
    I have now received a reply from the supplier and it, more or less, confirms what I thought - 'bike EFI is thrown by the increased resistance caused by inserting the lighted plug caps into the ignition leads.

    My understanding: Once lit, a neon lamp has an S-shaped negative resistance characteristic: increasing the current through the device increases the number of ions, thereby decreasing the resistance of the lamp and allowing even more current. Because of this characteristic, electrical circuitry external to the neon lamp must provide a means to limit current through the circuit or else the current will rapidly increase in an avalanche-like manner until the lamp is destroyed. For indicator-sized lamps, a ballast resistor is conventionally used to limit the current. I think the ballast resistor is the key to the problem.

    Suppliers response to my query:

    Ken,

    EFI bikes have been known to throw a code because the resistance is changed in the spark plug wire when using these caps on the spark plug.

    Almost anytime you change any of the electronics on an EFI bike you run the risk of throwing a code. The Harley sensors are designed to notice voltage and resistance changes to provide proper fuel management, so by changing the wires with something as simple as the LED cap it says something is now different.

    If you have any questions or need additional information, please don't hesitate to contact us. You may also visit us at http://jpcycles.custhelp.com/app to view our new customer service and tech self help interface. You can search for answers, send an email, or just browse the vast knowledge base.

    Jay.
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    Ken.
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