compression check process

[spacerust]

i am going to do a compression test on my outboard. it's a 75 Mercury 150hp. i know the general process but do i need to remove all the spark plugs wire while i do this or one at a time?

 

[blouderback]

Re: compression check process

Remove all the plugs and wires, then insert the tester in each cylinder one at a time, crank for 3-4 turns of the engine. The highest reading is your number. Make sure to disable the fuel injectors, and the coils, so you don't accidentally send fuel all over the place or risk one of those wires making a spark on the block.

Each cylinder should be within 10-15% of the other cylinders. That is, if the highest is 150 psi, then the lowest should be no less than 127 psi.

 

[spacerust]

Re: compression check process

how do i do that? unplug the coil? i was thinking of grounding the plugs wires.

 

[tashasdaddy]

Re: compression check process

turn the motor over till the guage quits rising. left the key off, and use a remote solenoid witch. couple of $ at auto parts store. you clip one lead to the big post on top of solenoid, and the other on the top small post. then you just push the button.

 

[Chris1956]

Re: compression check process

Spacerust, Leave the key shut off, throttle in neutral. You might remove the prop for safety reasons.

Connect a jumper wire to the thin yellow wire on the starter solenoid. Remove the spark plugs and install the gauge in the top hole. Now touch the jumper to the large red wire on the starter solenoid, and the motor should crank