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  #1   IP: 24.152.132.140
Old 06-22-2019, 03:43 PM
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Spark Test

Perhaps the most fundamental test we can perform on a non-running engine determines if the issue is fuel or spark related. Of the two, spark is much easier to test provided you're prepared. A simple test is to remove a plug or coil wire and hold it close to the engine block or head and watch for a spark as the engine is cranked but here are a few other ways that once in place may be even simpler still:

The Test Pen
We have mentioned it on the forum before, a cool test tool available on Amazon, eBay, etc. that does not require anything to be unplugged. Place the tip of the test pen on a spark plug wire and watch for the test light inside the pen barrel while cranking. This is a yes or no test, it does not offer any spark quality information.


The Spare Spark Plug
The purpose of the following is to have a testing means readily available without digging through lockers and spare parts boxes.

For quite some time Tom Thatcher (Thatch on the forum) has kept a spare spark plug laying loose on the engine's alternator/lifting eye bracket for a handy spark test. He found the plug picked up sufficient ground for a test just by sitting there. His test method was to pull a plug wire, put it on the test plug and crank. Recently he decided to make it a little more permanent (elegant?) and improve the grounding so he came up with a magnetic base spare plug mount that can be positioned anywhere on the engine.


As he and I tend to do, we each came up with our own spare plug mount systems and then compared notes afterward. Here is my version. It utilizes the lifting eye hole that we aren't using anyway.


Test Protocol
Remove a plug wire and place it on the spare test plug and crank the engine. Observe for spark (yes or no) and quality (blue = good, yellow = not so good). No spark = ignition problem, yes spark = fuel problem.
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prior boats 1987 Westsail 32, 1970 Catalina 22
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Old 06-22-2019, 06:27 PM
thatch thatch is offline
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Thanks Neil, It' obvious that any number of versions of this device can be made. I guess, ironically, that both Neil and I found the nice flat section of the lifting ring/alternator bracket, to be the ideal spot to place this gadget.
Tom
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  #3   IP: 24.152.132.140
Old 06-22-2019, 06:37 PM
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Quote:
Originally Posted by thatch View Post
I guess, ironically, that both Neil and I found the nice flat section of the lifting ring/alternator bracket, to be the ideal spot to place this gadget
We may be victims of our own boats (Catalina 30's) with zero clearance for anything higher than spark plug #1.
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1977 Catalina 30
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prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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Old 06-23-2019, 10:18 AM
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Man... the creative brain power between you two is amazing.

I'll never forget spending an evening with both of you.
I was mentally exhausted just listening to the back-n-forth conversation!
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Old 06-23-2019, 10:26 AM
thatch thatch is offline
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Jerry, I'd love to recreate that evening again sometime.
Tom
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Old 06-23-2019, 10:44 AM
Dave Neptune Dave Neptune is online now
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Great way to mount. Don't like seeing them on good running well maintained A-4's. I do like seeing them on engines with issues for diagnostics.

I too have used a spark plug for checking spark however it can be difficult to see the "jump of the spark". I recommend removing the ground lug from the spark plug. First this gives a larger gap to jump and it is far easier to see!!l You will also be able to "audibly" hear the "snap" as well as see the spark. The bluer the better. A spark with a yellowish flash is not good.

FYI, the hi-voltage ignition (the spark) needs to jump across a gap which is no big deal but when you add compression to the "chamber" this compression also offers up a great deal of resistance which is why you need a blue snappy spark!

Dave Neptune
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The Following 3 Users Say Thank You to Dave Neptune For This Useful Post:
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  #7   IP: 24.152.132.140
Old 06-23-2019, 11:23 AM
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Good info on removing the ground ear Dave. About having a spare plug on a good running engine, it's the same as having a fuel pressure gauge. It rides along harmlessly until it's needed and then you're glad you have it.
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