Disable spark?

[SilverShadow]

Thinking of carrying out a compression test on my M20 this weekend and been trying to search how to disable spark when testing?

Would disconnecting the cables under the diagnosis port be suffice?

[Speedtouch]

Just remove the king lead from the centre of the distributor. If you're running a compression test, you generally remove all the spark plugs anyway, so no real need to disconnect the ignition - just remove the fuel pump relay, and jam the throttle wide open.

[HairyScreech]

Actually pulling the crank sensor plug under next to the two temp sensors should mean you get no fuel either.
Might be a better bet.
Otherwise it is possible to leave the ignition off and run just the motor via the diagnostic port.

[Brianmoooore]

Just remove the king lead from the centre of the distributor.

Not good practice at all! Without a load the HT voltage will go through the roof and arc over either inside or outside the coil. If it arcs to the '-' terminal it sends a pulse of several thousands of volts straight back into the ECU, and although the ECU is designed with this possibility in mind, it's still playing Russian roulette.
Crank from the diagnostic socket (clue is in the name) is the way to do it.

[bmw9818]

remove terminals to coil and black tape it, and fuse 11 from fusebox to disable pump,

[BenHar]

Crank from the diagnostic socket (clue is in the name) is the way to do it.

+1

Ben