I'm not a mechanic / technician but on a 1999 Ford Explorer 4.0 L Over Head Valve V6 engine , bank 1 is the passenger side of the engine and I BELIEVE the oxygen sensor is in the outlet of the exhaust manifold
The Ford 4.0 liter OHV ( pushrod ) V6 engine has ( 1 ) timing chain
Bank 1 is the passenger side of the engine in your Ford Expedition
the number one cylinder on a Ford 4.0 L OHV engine is on the passenger side of the engine at the front of the vehicle. firewall 3 - 6 2 - 5 1 - 4 front of Ford Explorer 4.0 liter V6 ( OHV and SOHC engines )
On a Ford Expedition : Bank 1 is the passenger side of the engine
Bank 1 is the passenger side of the engine in your Ford Explorer
Bank 1 is the passenger side of the engine in a Ford Expedition
Bank 1 is the passenger side of the V6 engine in a Ford Ranger Bank 2 , the drivers side
Bank 1 is the passenger side of the engine and bank 2 is the drivers side of the engine in a Ford Expedition
The 4.0 L OHV engine has 1 timing chain
firewall 1-----2-----3 ( Bank 1 ) 4-----5-----6 ( Bank 2 ) front of Ford Freestyle
The Ford 4.0 liter OHV , V6 engine has ( 1 ) timing chain ( but the 1998 Ford Explorer XLT model , if it has the 4.0 liter V6 engine , would have the SOHC engine which has ( 3 ) timing chains )