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TOPIC: Need some advise on running a compression test

Need some advise on running a compression test 9 years 8 months ago #455

  • MarkS
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I need to run a compression check on an engine with electronic ignition. It's a Johnson, with individual coils for each of the four cyls. If I unhook the orange wires from each coil going to the ignition pack, will that work to not damage (burn up) anything in the ignition system? Any advise would be greatly appreciated.

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Mark

Re:Need some advise on running a compression test 9 years 8 months ago #458

If you do that the HV Capacitor in the power pack is still gonna be charged with nowhere for the juice to go. My thought would be to make sure the plug leads were all grounded to the block. BUT, I'd consult the shop manual 1st, or a qualified tech.

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Re:Need some advise on running a compression test 9 years 8 months ago #460

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Thanks Bruce, think I better do just that before I screw something up.

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Mark

Re:Need some advise on running a compression test 9 years 8 months ago #464

Mark, Disconect the battery and run jumper cables to the + connection on the starter and the - connection to the powerhead.

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Re:Need some advise on running a compression test 9 years 8 months ago #469

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Thanks, that makes sense. Just send power to the starter, not the ignition.

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Mark

Re:Need some advise on running a compression test 9 years 8 months ago #472

Mark, That's the idea. Plus you can just screw in the compression gauge and touch the cable to the starter (it will spark some, no harm done) and release after a few revolutions while you are at the motor watching the gauge. :)

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Re:Need some advise on running a compression test 9 years 8 months ago #495

Hello just put a spark plug on each lead and ground electrodes to block acn be done if you have a few alligator clips and wire.

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Re:Need some advise on running a compression test 9 years 8 months ago #497

Here is a link on how to do a compression and spark test.

themarinedoctor.com

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Re:Need some advise on running a compression test 9 years 8 months ago #502

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Many thanks, I really appreciate the help. One of the few good things about getting older is learning to get advise from someone who knows, instead of plunging in THINKING I know how to do it.

To quote Robert L, "I love this place"!

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Mark

Re:Need some advise on running a compression test 9 years 8 months ago #568

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Great news, the compression test came out good, all four holes read just shy of 150lbs! And thanks to the tutorial, I also ran a spark test and everything is snappin'! I devised my own spark plug grounding system, crude but effective. ;)
Attachments:

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Mark

Re:Need some advise on running a compression test 9 years 8 months ago #632

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Yup, like he said, that's how I do my tests, ignition off and jump the starter.
No risk of high voltage or ignition damage.
Randy

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