Compression Test

[RedDog]

Could someone please post a step-by-step instruction on how to accurately conduct a compression test? Things I want to know (besides everything since I know nothing) are:

Hot/warm/cold engine when testing
Pull 1 plug at a time or pull all and then test
Crank the engine for how long
Seems I have heard "ground the coil???" - or something like that - what does this mean and how do you do it

Thanks

[mphatc]

Reddog,

Engine should be at normal operating temperature
Remove all spark plugs.
Crank the engnie 4-5 compression strokes on the cylinder that you are testing, try to do the same amount of compression strokes on every cylinder.

Hold throttle wide open, on a 4 barrel carb just the two primaries need to be open.

Ignition, on an older conventional ignition, (points) ground the coil secondary lead, On an HEI, I unplug the small leads to the distributor.

If your boat has a fuel shut off valve in the engnie compartment it never hurts to close it, no need to pump fuel into the engine.

MPHATC

[Walt. H.]

And hopefully each cyl is within 10% of each-other.

[RickR]

Run a jumper from the coil wire to a good ground.
With your cam I would expect around 140 to 150 lbs.

I would do a leak down test also.

[RedDog]

Why do you ground the coil? Whats that do?

[RickR]

Spark has to go somewhere eek! And MSD will arc!
Better than burning up your Jacob's wires.