The combustion chambers are sprayed with a little quantity of 

penetrating oil after the spark plugs have been removed to increase the likelihood that the 

piston rings won't stick to the cylinder walls. 

When checking to determine whether the Challenger's starting 

motor can spin the engine, Davin disconnects the ignition coil to make sure no spark is started. 

An oil blow-by and compression check are both possible with a visual look via the spark plug apertures.