Compression test


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Saw a sign offering electronic compression test and decided to read about it. Can they be trusted or you still prefer taking the spark plugs off and use a dial?
 


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RonD

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Electronic is quick and works fine, but if you do have a low cylinder you will need to get your hands dirty with a gauge and some oil :)
If you are pulling plugs to add oil(wet test) might as well use a gauge at that point

And while I do trust electronic compression numbers I often don't trust the people doing the test, lol, unless it was me, and then I know for sure it was done wrong.

Electronic compression is done by the time difference on how much the crank slows down on each cylinders compression stroke, a low cylinder doesn't slow down the crank as much.
The numbers are also subject to Battery condition and/or starter motor condition.
But the same applies to mechanical gauges, slow cranking = lower numbers across the board.

Power balance test is done with engine running, it uses the crank speed, when a cylinder misfires crank speed slows momentarily.

Generally you would do a power balance test first, if a problem was seen then you would do the compression test, electronic or mechanical, to determine if compression issue was causing the problem.
Compression tends to be black or white, not intermittent, like spark or fuel can be, so once tested it can be taken off the table and you can focus on spark or fuel
 
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