I'm not familiar with the engine, but located the distributor and find the face which has numbers ranging from 1 to 6. Locate "1" and have a look at which cylinder it leads to. That said, It's probably the front left cylinder.
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You don't say which model of Mercury Vehicle , but :
front wheel drive is :
firewall
1-----2-----3
4-----5-----6
front of vehicle > driver
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rear wheel drive and 4x4
firewall
3 - 6
2 - 5
1 - 4
front of vehicle
( Helpfull )
On a Mercury Sable , V6 engine : firewall 1-----2-----3 4-----5-----6 front of vehicle > driver
Number one cylinder is the front passenger side in a V6 Dodge Magnum.
First cylinder in back on the passenger side is number one.
Number one is the front, driver side.
For the 2.5 4 cylinder, number one is the first cylinder from the passenger side.For the 3.5 V6 cylinder, number one is the first cylinder in back from the passenger the side.
On a Mercury Villager , V6 engine : firewall 1-----3-----5 2-----4-----6 front of vehicle > driver
where is the number one cylinder on an 88 Toyota 3.0 v6
On a 2001 Mercury Cougar , 2.5 liter V6 engine : firewall 1-----2-----3 4-----5-----6 front of vehicle > driver
125 Horsepower for 4 cylinder and approx.180Hp for v6 (1999 models)
On a 1999 Mercury Mountaineer , 4.0 liter V6 engine : firewall 3 - 6 2 - 5 1 - 4 front of vehicle
A 1996 Mercury Sable has either : One timing CHAIN on the 3.0 litre " Vulcan " V6 engine or Two timing CHAINS on the 3.0 litre " Duratec " V6 engine ( one CHAIN to each cylinder head )
Number one cylinder for v8 and v6 is always the front cylinder on the head that sticks further out on the front of the engine. The heads are offset on all v6 and v8 engines.