dcarver
Well-known member
Prepping for compression test. Need to ground plugs or no?
OK to spin engine w/o plugs grounded?
- Thread starter dcarver
- Start date
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ionbeam
2 FUN
Don, DON CARVER, be aware, feel the Omnipotent force, look inside, what does it tell you, can you feel the correctness of it? What does the FSM say?
on 4/1
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I'd leave the plugs sitting on the workbench. But that's just me.
dcarver
Well-known member
Thanks guys. Appreciate the quick response.
mcatrophy
Privileged to ride a 2018 FJR1300AS
Use plugs, their outer held to the engine, so they spark near to normal. It is the spark that limits the voltage out of the coil, hence the electrical stress on the coils' insulation. I'd much rather short the coils' outputs to engine than leave them open circuit, much safer electrically.
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FJRay
Well-known member
I've always shorted the coils but that may not apply to a modern engine. Can't hurt and probably cheaper than buying coils.
rushes
Well-known member
I've never tried it and the bike is not here.
Will it crank with the kill button off?
Will it crank with the kill button off?
ionbeam
2 FUN
Won't crank with the kill button off.
By now Dave will have read the FSM
which does not call for grounding the plugs or coils, it simply says to unplug the spark plug caps. Back in the day, you could fry a lot of expensive electronics by not grounding the coils, especially on Furds.
Point taken that there is a lot of energy in the coils lookin' to get out if they aren't grounded and high voltage is evil in the way it seeks out a path to ground, even if it has to leak up the primary side back into the control circuitry or preferably, through a careless mechanic. Since Yamaha doesn't mention or recommend grounding the plugs and only says to unplug the caps I would assume it's safe to leave the caps open. But, please use care, the high voltage in the coils can drop a big, big hammer on ya.
By now Dave will have read the FSM
Point taken that there is a lot of energy in the coils lookin' to get out if they aren't grounded and high voltage is evil in the way it seeks out a path to ground, even if it has to leak up the primary side back into the control circuitry or preferably, through a careless mechanic. Since Yamaha doesn't mention or recommend grounding the plugs and only says to unplug the caps I would assume it's safe to leave the caps open. But, please use care, the high voltage in the coils can drop a big, big hammer on ya.
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rushes
Well-known member
Kinda offtopic? Sorry...
Flashback story...
Once upon a time, a goober was changing carbs on an old Mustang and he thought it would be a good opportunity to do a compression check.
Spark plugs were removed and plugged into the caps and laid perfectly grounded on intake bolts.
Tester was screwed in to #1 hole and engine was cranked several revolutions.
Goober didn't think about fuel pump pumping and fuel line aimed right at sparking spark plugs....
Flashback story...
Once upon a time, a goober was changing carbs on an old Mustang and he thought it would be a good opportunity to do a compression check.
Spark plugs were removed and plugged into the caps and laid perfectly grounded on intake bolts.
Tester was screwed in to #1 hole and engine was cranked several revolutions.
Goober didn't think about fuel pump pumping and fuel line aimed right at sparking spark plugs....
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I usually connect the plugs and lay them against the head but away from the spark-plug holes. I remember reading long ago that some ignition systems don't like sending a spark to a plug that's not there (may not be true anymore of course as others have indicated). However, I haven't actually done a compression test on my '05 yet... no reason to yet but perhaps at the next plug/valve check just for fun.
Mr. BR
Mr. BR
dcarver
Well-known member
KrZy8 lives on!
Will start another post with latest adventure - but
Compression is as follows cyl 1=170, 2=190, 3=178, 4=180. Throttle WFO.
2 readings averaged.
Car battery charger on battery, cold engine.
First set of numbers about 5-10 psi lower than second.
Good enough numbers?
Will start another post with latest adventure - but
Compression is as follows cyl 1=170, 2=190, 3=178, 4=180. Throttle WFO.
2 readings averaged.
Car battery charger on battery, cold engine.
First set of numbers about 5-10 psi lower than second.
Good enough numbers?
FJRay
Well-known member
I would say that's pretty damn good. All within 10%.
RaYzerman19
Go Wings!
Disregard the FSM, you are to hold the bare ends of the coil wires with your bare hands while standing on wet concrete, then crank 'er over.
mcatrophy
Privileged to ride a 2018 FJR1300AS
Don't really need the wet concrete, on the OP's 2006 it's a lost spark system, the current flows between plug 1 and 4, and between 2 and 3. No "ground" needed. But is does help if you can hold leads from plugs 1 and 2 in one hand, and 3 and 4 in the other.
(Illustrative diagram only, not FJR specific. Click on image for larger view.)
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mobilemike
Member
It might not be required anymore but I either ground the plug wires or disconnect the power wire to the coils. Eliminating the spark is what I want so I do not leave the spark plug connected to the wire and just ground the side electrode to the head or block. It will still spark and getting hit by 20k to 40k volts from the plug is not fun. Not to mention it igniting stray fumes from the engine
