DeTomaso Mailing List: October 99, Message #94

In a message dated 9/27/99 5:32:54 AM, DJFranck@equilon.com writes:

<< Do the cold number(s for compression tests) tell me anything?  I did three 
cyls and get 170, 170, 155 >>

The way I was taught is, first pull all plugs, the coil wire AND the hot lead 
to the coil (lo-tension). This is for electronic ignitions; the really hot 
ones MUST have a place to discharge the hi-tension voltage or you may get a 
flash-over in the module, which will destroy it. 2nd, block the throttle wide 
open w/no choke. 3rd, crank the engine 4 times to be sure you get exactly 1.0 
compression strokes. All readings should be +- 15 psi. If not, squirt a small 
quantity of oil down one plug hole, and repeat the test. If any values come 
UP significantly, you've got a ring seal problem. If any low ones are still 
low & don't move, you've got a valve seal problem. In both cases, the trouble 
is now in a known cylinder. Whether the motor is hot or cold is irrelevant. 
The actual value is also irrelevant since no two compression gauges will read 
the same. A leak-down test run later will tell you more about the motor. Good 
luck- J DeRyke