How to perform compression check on 240 efi m2 engine?

[fender1983@gmail.com]

I heard i need to ground spark plugs when doing compression check. Is it true? If yes, how to do this?

Manual from 2001 doesn't say anything about grounding them:

"
1. Remove spark plugs.
2. Install compression gauge in spark plug hole.
3. Hold throttle plate at W.O.T.
4. Crank engine through at least four compression strokes to obtain highest possible read- ing.
5. Check and record compression of each cylinder. Variation of more than 15 psi (103.5 kPa) between cylinders indicates that lower compression cylinder is in some way defec- tive such as worn or sticking piston rings and/or scored piston and cylinder.
6. Compression check is important because an engine with low or uneven compression cannot be tuned successfully to give peak performance. It is essential, therefore, that improper compression be corrected before proceeding with an engine tune-up.
7. Cylinder scoring: if powerhead shows any indication of overheating, such as discolored or scorched paint, visually inspect cylinders for scoring or other damage as outlined in Section 4: Powerhead."

 

[fender1983@gmail.com]

So i am confused. The mercury manual says just remove spark plugs and crank the engine.

Sea Doo manual says to never crank engine without connecting spark plug wires to grounding device (page 54)

 

[Coastiejoe]

When holding it WOT, it is suppose to disable the spark. That said, grounding the wires would not hurt any.

The Merc is a. It if it own beast. Not a lot of us know them very well by comparison.

On non-Merc stuff, there are grounding posts for the wires.

 

[fender1983@gmail.com]

When holding it WOT, it is suppose to disable the spark. That said, grounding the wires would not hurt any.

The Merc is a. It if it own beast. Not a lot of us know them very well by comparison.

On non-Merc stuff, there are grounding posts for the wires.

Thank you!

 

[fender1983@gmail.com]

So, compression numbers seem good. About 128-130 psi on all cylinders.

We couldn't move lever to full throttle in neutral position, it only moves when engine is in forward gear(didn't try reverse).
Engine will not crank in forward.
We disconnected all spark plug wires, removed all spark plugs. Tried disconnecting what we thought was a fuel pump. There is a square thing right next inline fuel filter. It was ticking if we turn on ignition. After removing fuse next to it and disconnecting relay (big connector next to inline fuel filter) it stopped ticking.

We performed compression check in neutral with closed throttle.

Hopefully we didn't messed anything up. No fuel came out through cylinders.

What you guys think? Could we damage coils?

 

[Tim75]

Remove all plugs. install gauge. Remove ignition key. Full throttle. EXTREME CAUTION! At the starter solenoid-- from battery terminal to small terminal- jump those two.

This bypasses the ignition system. And ALL safeties.

 

[Kwik_uk]

Grounding or not grounding them doesn't make any difference on these. Just make sure they're not touching anything - or you (you'll only make this mistake once) and crank. Do it for about 4-5 sec per cyl, but leave a minute in between so you don't boil the starter.

Lower cylinder on either sides are the usual suspects on this powerhead, as they get the worst deal on cooling.
Worth checking your thermostats at the top of each head. I swap mine out every year as I use in salt.

I've got the outboard version of this engine on my ski boat. Powerhead is the same though.

 

[fender1983@gmail.com]

Thanks again, guys! Looks like Thursday is a sea trial. Can't wait to pick it up