1979-1993 & 94 Conv [Subscribe to Daily Digest] |
the rule of thumb is about a 10% variance. You're a little bit over.
Better readings with engine warm
This may be more than you want...but,
My procedure (whether the same as or different from yours, it's better to use the same procedure so results form one time can be compared to previous and future readings.):
I usually pull all the plugs. screw in the tester (one that you have to hold in place is not as reliable as one you can screw in and tighten against an o-ring) floor the gas pedal and crank it so it spins 5 times. (unnhr - unnrh - unnrh - unnrh - unnrh). It is interesting to also do it with one unnrh, more on that later.
This is a hot-dry reading. the rule of thumb is 10% variance. If there is a large drop on one (say 100-140-14--150) then try the "wet" process. This "assumes" that the drop on one hole is caused by loss of compression on that hole's ringset. So take an oil (regular engine oil) oilcan and give abut 3-4 squirts into each plug hole---insert the spout in as far ands you can and if touching a piston, move it around a little. You are trying to infuse engine oil between the cylinder walls and the piston.
repeat the 5-grind test. Are the readings different (they will usually be a little higher. Not always, though, because sometimes you've not put enough in or it didn't make any difference...which is more common with a warm test than a cold one If the low hole in the dry test comes up, there's compression loss past the rings.
At which point a leak down test should be performed but that requires a compressed air source and special gages that most folks don't have handy in their garage. A leakdown test can differentiate between leaking intake/exhaust valves, leaking valve guides, leaking rings, etc.
On the "one spin" compression. Any engine will build up to a xxx compression reading. But a single spin reading gives a snapshot that might be different. It will be lower, maybe 30 points or more. This is the compression that most engine will attempt starting on. If you have a 50 psi reading in one hole and 100 in the others, you probably have a starting problem (it takes grinding a while, more than it used to). This hole might even build up to not be the low one on a 5-spin sequence. But it is worth noting and might be instructive later.
FWIW
posted by 68.122.22...
, Tue, 25 Sep 2007 17:55:43, Wed, 26 Sep 2007 12:40:39
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