General Category > Engine related issues

Ignition Coils

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R1200rme:

--- Quote from: WayneC on September 22, 2016, 12:00:48 PM ---
--- Quote from: R1200rme on September 22, 2016, 11:25:42 AM ---My understanding is the plug needs to be grounded BEFORE cranking the engine or coil damage may ensue.

--- End quote ---
Some one has been leading you astray, an open circuit will not cause damage and if you ground the plug while cranking at the worst there will be a little initial surge current as you ground the plug nothing to be too concerned about though.

--- End quote ---
Thanks for the clarification.

Borgia:
Every manual that I have ever read advises that spark plugs should be grounded if you are doing anything that will cause the ignition to want to fire (e.g. checking compression). That's because in normal operation the secondary coil voltage will only climb to the point where the spark jumps the gap in the plug. With no ground on the plug the voltage keeps climbing to the point where damage to ignition components could occur - especially expensive electronic components.

WayneC:

--- Quote from: bmwroadsterca on September 23, 2016, 02:38:14 PM ---Every manual that I have ever read advises that spark plugs should be grounded if you are doing anything that will cause the ignition to want to fire (e.g. checking compression). That's because in normal operation the secondary coil voltage will only climb to the point where the spark jumps the gap in the plug. With no ground on the plug the voltage keeps climbing to the point where damage to ignition components could occur - especially expensive electronic components.

--- End quote ---
If that was the case then ignition components would be damaged when a plug lead or resistive element in a plug went open circuit. You may also stop and consider what components there are on the secondary side of the coil. Opening up an ECU and looking at the output stages used in the ECU's then reading the data sheets for those components would also perhaps alter your outlook. I have opened and repaired ECU's, I have the data sheets for the ICs in BMSC/BMSK/BMSE on file so I know what the protection levels are in the components on the primary side of the coil.

Some of us are also now firing plugs at a far higher voltages and using capacitive plugs producing higher current loads on the coils without failures

Whenever anyone tries to hold a plug in place while hitting the starter there will often be momentary open circuits. If you really want to feel safe for peace of mind when checking make up a lead with an alligator clip to go to earth and a length of bared wire at the other end to wrap around the base of the plug, it is far easier that way.

Borgia:
"If that was the case then ignition components would be damaged when a plug lead or resistive element in a plug went open circuit."

Not at all. The point is that damage COULD occur. The recommendation to ground the plug is to mitigate the higher risk that damage may occur when extreme voltages otherwise result.

"You may also stop and consider what components there are on the secondary side of the coil. Opening up an ECU and looking at the output stages used in the ECU's then reading the data sheets for those components would also perhaps alter your outlook."

Well having worked in electronics for 35 years I too have seen component specs and nothing therein alters my outlook. A spec is not a licence to incur unnecessary risk.

" I have opened and repaired ECU's, I have the data sheets for the ICs in BMSC/BMSK/BMSE on file so I know what the protection levels are in the components on the primary side of the coil."

"Some of us are also now firing plugs at a far higher voltages and using capacitive plugs producing higher current loads on the coils without failures"

"Whenever anyone tries to hold a plug in place while hitting the starter there will often be momentary open circuits. If you really want to feel safe for peace of mind when checking make up a lead with an alligator clip to go to earth and a length of bared wire at the other end to wrap around the base of the plug, it is far easier that way."

That is how I do it - but alligator clips at both ends - one clipped onto the ground electrode on the plug and the other to ground. If the coil is built into the spark plug cap then just unplugging it from the harness suffices since that removes the coil primary from the circuit and there will be no high voltages generated on the secondary.

WayneC:
This thread has served it's purpose and run it's course Paul has a clear answer on whether there is oil testing in the GS911 and Dealer Diags so there is little point in OT discussion re plug/coil testing. I would suggest a little more thought and reading re coils and IGBT's used to drive the primary side of the coils

On Semi MGP20N35CL, Fairchild ISL9V3040D3S, ST VB525SP-E would be a good starting point

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