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driving me nuts

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Old Feb 3, 2022 | 06:40 PM
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Second Street Cycles's Avatar
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Default driving me nuts
got a 2008 heritage we just redid the engine on, wont start.... no spark.
crank sensor is new, injectors squirt, has power to the coil, coil is good, but no spark?
we OHM'd the wires from coil harness to the ECM harness and they check out
anyone got any ideas?
 
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Old Feb 4, 2022 | 07:10 AM
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Are you checking your spark with plugs installed and using a third plug or a spark checker?
 
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Old Feb 4, 2022 | 08:33 AM
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Checking with plugs out, grounded to jugs
 
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Old Feb 4, 2022 | 08:43 AM
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You will not get spark using that method. Must have a plug in the cylinder for spark to occur.
 
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Old Feb 4, 2022 | 11:41 AM
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Get an inline spark tester at your favorite auto parts store, around $10. You need to have compression for the ECU to send a spark signal.
Should also check for codes.
 
Last edited by nevil; Feb 4, 2022 at 11:47 AM.
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Old Feb 4, 2022 | 06:01 PM
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Plug wires reversed
 
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Old Feb 5, 2022 | 07:18 PM
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One and done anyway
 
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Old Feb 5, 2022 | 08:07 PM
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Originally Posted by nevil
Get an inline spark tester at your favorite auto parts store, around $10. You need to have compression for the ECU to send a spark signal.
Should also check for codes.
Educate me please, how is the compression sensed? Only sensors I knew of in the heads were temp sensors and acr's on newer bikes.
 
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Old Feb 5, 2022 | 08:27 PM
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Originally Posted by chopper_man
Educate me please, how is the compression sensed? Only sensors I knew of in the heads were temp sensors and acr's on newer bikes.
ECM senses flywheel deceleration via crank sensor on compression strokes and cross references with MAP sensor and missing flywheel reluctor tooth to know phase. When you crank with no plugs it doesn't see the deceleration and will not throw spark.
 
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Old Feb 7, 2022 | 07:42 AM
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Originally Posted by chopper_man
Educate me please, how is the compression sensed? Only sensors I knew of in the heads were temp sensors and acr's on newer bikes.
Originally Posted by Ed Ramberger
ECM senses flywheel deceleration via crank sensor on compression strokes and cross references with MAP sensor and missing flywheel reluctor tooth to know phase. When you crank with no plugs it doesn't see the deceleration and will not throw spark.
Class dismissed

FWIW, I had no idea, lol
 
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