1994 Ford Aerostar

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
YOU WOULD BE ABLE TO HEAR THE LEAK THROUGH THE ADJACENT SPARK PLUG HOLE VERY EASILY USING A PIECE OF RUBBER HOSE AS A STETHOSCOPE. YOU CAN ALSO ROTATE THE MOTOR AS YOU ARE LISTENING AS YOU CAN HEAR THE VALVES OPENING AND CLOSING AND YOU CAN SEE THE PRESSURE IN THE CYLINDER GO UP IF YOU PUT A STANDARD DIAL TYPE TIRE GAUGE ON A TEE ADAPTER TO THE HOSE WHEREAS IF THE CYLINDER HAS PRESSURE AND YOU CAN HEAR A HISSING IN THE ADJACENT CYLINDER THERE IS A DEFINITE LEAK. BUT IF THE TWO EXHAUST VALVES ARE OPEN SIMULTANEOUSLY YOU WOULD ALSO BE ABLE TO HEAR THE PRESSURE GOING OUT OF ONE CYLINDER THEN DOWN THE EXHAUST MANIFOLD AND UP INTO THE OTHER CYLINDER SO YOU CAN TRY TO FIND THE BEST CRANKSHAFT ANGLE WHERE THE HISSING FROM THE LEAK IS MOST DISTINCT.