Spark but no fire
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Stage I
Joined: Jan 2023
Posts: 1
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From: Show Low, AZ
Spark but no fire
01 Roadking has great blue spark on rear cyl. when plug wire is held away from spark plug, when attached to plug there is no spark. I installed new HD plug, same problem?
Seasoned HDF Member
Joined: Jun 2014
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From: pacific northwest
Check the condition of your cables , found many times over the years of how a plug will fire in open air but not under compression. You said tried a new plug so the cable would be the next thing I would check. Sometimes a cable can have bad insulation and fire ok in the air but under compression will leak to ground someplace else.
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Joined: Mar 2021
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From: backwoods
You are supposed to have the plug in the bootm and grounded. As tiny child I was told to never do what you have done out of concern from damaging the electronics. Don't know if true, but I have never done it
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From: Honah Lee
The service manual says with both plugs removed and properly grounded to the head with wires attached, you will not get a spark on a 2004 system.
You need at least one plug in and compression on it. It's a system protection and also prevents it from throwing error codes maybe.
Need to use Harley branded low resistance plugs for the knock suppression system to work correctly. NGK will work if you don't flogg it and live in the mountains or steep hills.
You need at least one plug in and compression on it. It's a system protection and also prevents it from throwing error codes maybe.
Need to use Harley branded low resistance plugs for the knock suppression system to work correctly. NGK will work if you don't flogg it and live in the mountains or steep hills.
Seasoned HDF Member
Joined: Sep 2008
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From: San Diego, CA
I use an inline spark tester to check for spark on my HD bikes...
Some need compression, some need to be grounded and some need both... An inline tester satisfies all of them...
There are many makes of inline spark testers out there... here is just one choice...
https://www.summitracing.com/parts/l...hoCTAEQAvD_BwE
Some need compression, some need to be grounded and some need both... An inline tester satisfies all of them...
There are many makes of inline spark testers out there... here is just one choice...
https://www.summitracing.com/parts/l...hoCTAEQAvD_BwE
HDF Community Team
Joined: Nov 2012
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From: USA
The service manual says with both plugs removed and properly grounded to the head with wires attached, you will not get a spark on a 2004 system.
You need at least one plug in and compression on it. It's a system protection and also prevents it from throwing error codes maybe.
You need at least one plug in and compression on it. It's a system protection and also prevents it from throwing error codes maybe.
The manual poorly alludes to the spark plugs being ungrounded and therefore not sparking. The inference is in the next paragraph, telling you to use a grounded tester instead.
The manual also instructs to have both plugs installed while using the spark tester. Thats unnecessary.
So sayeth a guy with an 04 that sparks the plugs just fine when theyre grounded outside the engine.
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Seasoned HDF Member
Joined: Sep 2008
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From: San Diego, CA
There is nothing in the engine that detects compression, and nothing that shuts off spark if none is present.
The manual poorly alludes to the spark plugs being ungrounded and therefore not sparking. The inference is in the next paragraph, telling you to use a grounded tester instead.
The manual also instructs to have both plugs installed while using the spark tester. Thats unnecessary.
So sayeth a guy with an 04 that sparks the plugs just fine when theyre grounded outside the engine.
I just assumed (yes, I know about assuming) that the manual saying to have the plugs installed, was due to some need for compression to get spark...
Electrical issues not being my strong suit, I sometimes give the ECM/BCM/Sensors more credit than they deserve...
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Joined: Mar 2010
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From: Honah Lee
There is nothing in the engine that detects compression, and nothing that shuts off spark if none is present.
The manual poorly alludes to the spark plugs being ungrounded and therefore not sparking. The inference is in the next paragraph, telling you to use a grounded tester instead.
The manual also instructs to have both plugs installed while using the spark tester. That’s unnecessary.
So sayeth a guy with an 04 that sparks the plugs just fine when they’re grounded outside the engine.
The manual poorly alludes to the spark plugs being ungrounded and therefore not sparking. The inference is in the next paragraph, telling you to use a grounded tester instead.
The manual also instructs to have both plugs installed while using the spark tester. That’s unnecessary.
So sayeth a guy with an 04 that sparks the plugs just fine when they’re grounded outside the engine.
Actually, the 04 has ion sensing or the EFI system. A long while back, there was an electrical engineer on here who said he engineered the TC electronics and said it monitors it in the coil for feed back to the ECM.
I have never checked it myself.
But I have seen many cases on here where it's true
This is what it says. And that's not exactly what you said. It's saying use tester with plugs installed. You can use a third plug as a tester.
Will post the picture shortly. From my 04 Diagnosis manual.
The first poster has not identified if his is EFI or carb.
Last edited by Jackie Paper; Jan 8, 2023 at 10:06 PM.
