Spark but no fire
Seasoned HDF Member
Joined: Dec 2005
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From: poway
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.
Seasoned HDF Member
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Posts: 19,894
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From: poway
BTW. I don't know about the stock carbed ignition needing compression to spark. I do know that the aftermarket ones will spark. I suspect that they use front cylinder timing if they can't detect compression and fire both plugs. That way the font cylinder don't see too much advance..
HDF Community Team
Joined: Nov 2012
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From: USA
Yes, the ecu or perhaps a different module, will detect a change in the spark itself from pre-ignition, and alter the ignition timing. This is a refinement of knock detection and replaces the old bolt-on knock detectors. There is not detection of compression, and it does not prevent a spark from happening.
And yes, if the engine is cranked over very slowly, there may not be a signal detected at the crankshaft hall sensor, and no spark takes place. This is down towards hand cranking speeds.
The manual is wrong saying there will be no spark at the plugs outside the engine, and the manual is wrong saying the spark plugs have to be installed for there to be spark at the tester. There will be a spark across the plugs outside the engine, if the plug is grounded.
And yes, if the engine is cranked over very slowly, there may not be a signal detected at the crankshaft hall sensor, and no spark takes place. This is down towards hand cranking speeds.
The manual is wrong saying there will be no spark at the plugs outside the engine, and the manual is wrong saying the spark plugs have to be installed for there to be spark at the tester. There will be a spark across the plugs outside the engine, if the plug is grounded.
Seasoned HDF Member
Joined: Sep 2008
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From: San Diego, CA
Delphi systems may or may not spark. It depends on whether it can detect crank slowing on the rear cylinder. Carbed and MM EFI don't have this issue.. Carbed because it don't have injectors to fire and MM EFI because it has a cam sensor. On Delphi, the crank slowing is the only way to determine cam phasing.
Max forgive my electronics deficient brain....
Are you saying the Delphi systems need to detect the crank slowing on the rear cylinder, used to determine proper cam phasing, before they will spark... ? And the engine needs compression for this rear cylinder slowing, during cranking, to occur...?
Or have I totally missed the point...?
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,894
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From: poway
Max forgive my electronics deficient brain....
Are you saying the Delphi systems need to detect the crank slowing on the rear cylinder, used to determine proper cam phasing, before they will spark... ? And the engine needs compression for this rear cylinder slowing, during cranking, to occur...?
Or have I totally missed the point...?
Are you saying the Delphi systems need to detect the crank slowing on the rear cylinder, used to determine proper cam phasing, before they will spark... ? And the engine needs compression for this rear cylinder slowing, during cranking, to occur...?
Or have I totally missed the point...?
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,894
Likes: 8,002
From: poway
Yes, the ecu or perhaps a different module, will detect a change in the spark itself from pre-ignition, and alter the ignition timing. This is a refinement of knock detection and replaces the old bolt-on knock detectors. There is not detection of compression, and it does not prevent a spark from happening.
And yes, if the engine is cranked over very slowly, there may not be a signal detected at the crankshaft hall sensor, and no spark takes place. This is down towards hand cranking speeds.
The manual is wrong saying there will be no spark at the plugs outside the engine, and the manual is wrong saying the spark plugs have to be installed for there to be spark at the tester. There will be a spark across the plugs outside the engine, if the plug is grounded.
And yes, if the engine is cranked over very slowly, there may not be a signal detected at the crankshaft hall sensor, and no spark takes place. This is down towards hand cranking speeds.
The manual is wrong saying there will be no spark at the plugs outside the engine, and the manual is wrong saying the spark plugs have to be installed for there to be spark at the tester. There will be a spark across the plugs outside the engine, if the plug is grounded.
HDF Community Team
Joined: Nov 2012
Posts: 6,189
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From: USA
I will concur with the differences, when it comes to modern solid state components.
I was referring to the fundamentals of the Hall Effect, a perturbance of voltage in a conductor. As discovered well over a century ago, long before solid state circuitry was discovered.
Early electronic ignitions used a simple 2-wire coil and the Hall effect for ignition timing. In fact it’s still used to this day in point conversion kits.
It still is a Hall effect that is detected by the sensor, be it a hall sensor or a VR type. But yes, the sensors themselves are indeed different.
I was referring to the fundamentals of the Hall Effect, a perturbance of voltage in a conductor. As discovered well over a century ago, long before solid state circuitry was discovered.
Early electronic ignitions used a simple 2-wire coil and the Hall effect for ignition timing. In fact it’s still used to this day in point conversion kits.
It still is a Hall effect that is detected by the sensor, be it a hall sensor or a VR type. But yes, the sensors themselves are indeed different.
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Road Warrior
Joined: May 2017
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From: Phoenix
Harbor freight $5. Don't have to remove spark plugs. Since I bought it I haven't shocked myself, throwing a screwdriver I was using across the floor, nor have I ignited that gas air flame thrower shooting out the spark plug hole as I grounded the spark plug to close to the hole.
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