The Ford Barn - View Single Post - #4 cylinder misfiring. Spark good. Compression 53 psi

100IH · 12-02-2016, 02:28 PM

It is simply a check for an intermittent valve that is not sealing. Frequently, a conventional compression test might not show an open valve at cranking speed if the issue is marginally sticking open. At running speeds it will show up by dropping to zero with the gage. A compression test gets a reading by cranking until the pressure levels off to the best reading and if it had a zero reading on one power stroke, it might not show as with a broken spring. The plus is, if you find a floating valve, you are already to proceed with a cyl. leakage test, which answers the issue completely. This test is only for the head scratcher problem that is inconsistent.

12-02-2016, 02:28 PM	#16
100IH Senior Member Join Date: Dec 2011 Location: SW Idaho Posts: 970	Re: #4 cylinder misfiring. Spark good. Compression 53 psi It is simply a check for an intermittent valve that is not sealing. Frequently, a conventional compression test might not show an open valve at cranking speed if the issue is marginally sticking open. At running speeds it will show up by dropping to zero with the gage. A compression test gets a reading by cranking until the pressure levels off to the best reading and if it had a zero reading on one power stroke, it might not show as with a broken spring. The plus is, if you find a floating valve, you are already to proceed with a cyl. leakage test, which answers the issue completely. This test is only for the head scratcher problem that is inconsistent.