failure to ground

[hl]

I bought a project boat with a friend. We have been working on it off and on togeather. The last couple of weeks I have been unable to work on it. He was trying to check the compression and did not ground the spark plug wires. He now tells me the motor has no spark to the plugs. this is a 1983 90 hp. Is this more damaging to the switch box or the coils or the power pak.

 

[Faztbullet]

Re: failure to ground

He was trying to check the compression and did not ground the spark plug wires. He now tells me the motor has no spark to the plugs. this is a 1983 90 hp. Is this more damaging to the switch box or the coils or the power pak.

According to Shaun@ CDI and he also does training for AMTECH, this is for safety only and any damage from not grounding is a wife tale. Grounding them ensures you are not shocked during testing and it does not ignite a fuel charge/vapor blown from spark plug holes causing a fire.... It being a 1983 I'll bet the stator has given up which is common issue....

 

[CharlieB]

Re: failure to ground

Still he must test each component of the ignition to be positive of the faulty part as there is NO RETURN on electrical parts.

CDIElectronics has an excellent Ignition Troubleshooting Guide available for FREE on their support pages, download it, follow the well written directions to test and determine the exact cause of the failed ignition BEFORE ordering any electrical parts.

 

[hl]

Re: failure to ground

Thanks, I checked out the site. Seems to be a great site to learn about electronic problems. When we have time we will start from the spark plugs and work toward the stator. Thanks again

 

[Texasmark]

Re: failure to ground

The storage capacitor stores energy that is released when the switch in the CDM is triggered. The energy is dumped into the high voltage transformer primary. The output of the transformer can be as high as 40,000 volts if unloaded:

With a spark gap to ground the voltage rises until the gap can no longer hold it off and gets no where near 40,000 volts under normal conditions....10, 15,000 volts maybe.

If the spark plug is not grounded, you could put a wire across the gap and it wouldn't make any difference to the high voltage transformer as there is no return path for the current it's trying to get going with all that voltage and the voltage stays there until it is dissipated in the transformer, reflected back to the primary, hence the trigger circuit,.....or is dissipated in whatever arcs as a result of the excessive voltage. The energy stored in the capacitor 1/2 CV(exp2) is going to be dissipated somewhere when it leaves the capacitor.

If the spark plug were grounded, to the engine block you will not experience the excessive voltage.

So, to not have to worry about what if, I always ground my plug cases (threads) when testing with them out of the engine and have the high voltage leads connected to the plugs.

Mark