Poll; How do you disable the ignition system for compression testing?

[njlarry]

I've come across three methods for disabling the ignition system for compression testing. Which method do you use and why? Any other method you prefer?

Method A; simply pull the safety lanyard

Method B; either remove the secondary lead from the coil and distributer cap or just remove it from the distributer cap and ground it.

Method C; remove both of the primary leads to the coil and ground them both.

Is there a difference with type of ignition system?

Thanks for any help.

 

[burroak]

Re: Poll; How do you disable the ignition system for compression testing?

Method D: Remove the spark plugs. Less of a draw on the battery and you get a higher spin rate.

 

[Bondo]

Re: Poll; How do you disable the ignition system for compression testing?

Ayuh,..........

I usually just Pop All the Sparkplugs Out....
Screw in the Gauge,+ Let'er Rip.........

The Plug Wires don't Hurt if you're not hanging on to them........

 

[Scaaty]

Re: Poll; How do you disable the ignition system for compression testing?

Lanyard grounds the system..

 

[chargedstang89]

Re: Poll; How do you disable the ignition system for compression testing?

I always just unplug the coil wire that goes to the distributor....no spark will ever get to the distributor and then to the plugs using this method.

 

[Coors]

Re: Poll; How do you disable the ignition system for compression testing?

All the plugs are supposed to be out, and the carb wide open.

 

[Don S]

Re: Poll; How do you disable the ignition system for compression testing?

Method A; simply pull the safety lanyard

This one may not work, depending on the type igniion system you have. With a points type ignition when cranking, you will still have power to the ignition, it will have power as long as the starter solenoid is engaged.

Method B; either remove the secondary lead from the coil and distributer cap or just remove it from the distributer cap and ground it.

Again, depending on type of ignition system, with some electronic ignitions, without the path to ground you can damage the ignition module or amplifier. depending on what it has.

Method C; remove both of the primary leads to the coil and ground them both.

Not necessary, and takes tools and it's a waste of time.

To answer your question, Non Of The Above

All you have to do is pull the Hi-Voltage lead out of the distributor cap and ground it.

To do a compression test, you MUST pull all the spark plugs, and do it like this.
Compression Test

 

[njlarry]

Re: Poll; How do you disable the ignition system for compression testing?

Thank you all, Gentlemen for sharing your experience. Hope some others are learning as much as I am.
Don, extra thanks for the detailed answer. Forgive two dumb questions but in method one, if the ignition system still has power with the lanyard removed, what keeps the engine from starting? Second dumb question..if the system is not electronic why does the high tension lead from the coil have to be grounded? And one last dumb question ..just to make sure, is the BID system considered "electronic"?

 

[Don S]

Re: Poll; How do you disable the ignition system for compression testing?

method one, if the ignition system still has power with the lanyard removed, what keeps the engine from starting?

It will start, even with the lanyard removed. But, it will not keep running after you let the key off the Start (Crank) position. There is a bypass wire attached to one of the small solenoid terminals that supplies power to the coil with cranking voltage for starting.

Second dumb question..if the system is not electronic why does the high tension lead from the coil have to be grounded?

It won't damage anything, but you will have an open spark somewhere on the engine where the wire is dangeling. It could spark the gas in the carb, or even touch you and make you jump and do something you wished you didn't. So if you ground it properly it prevents possible problems.

And one last dumb question ..just to make sure, is the BID system considered "electronic"?

The BID system (Prestolite) was used by Volvo for many years, it was an electronic ignition, but the distributor still had mechanical advance.
You could also removed the two primary wires from the coil that go to the distributor. But grounding the coil wire works just as well.
One note, a simple ground jumper wire with an alligator clip on each end assures a solid ground if you are unsure of where you ground the coil Hi Voltage lead.

 

[njlarry]

Re: Poll; How do you disable the ignition system for compression testing?

Understood. Many thanks!!!!
Out.