The 1998 Ford F-150 came standard with a 205-horsepower, 4.2-liter V-6 engine and had two V-8 engines available as options: a 220-horsepower, 4.6-liter and a 235-horsepower, 5.4-liter V-8. The firing order on these engines is the order in which the cylinders are supposed to receive spark. When you perform a tune-up or any other repair that involves removing any spark delivery component, you must set the firing order according to Ford's specification. This is why, when changing plugs or plug wires, you should change one at a time, to maintain the correct firing order.
Starting on the passenger side front of the 4.2-liter engine and moving clockwise, the cylinder numbers are 1-2-3-6-5-4. The firing order of the 4.2-liter engine is 1-4-2-5-3-6.
The cylinder numbers on the 4.6-liter engine are 1-2-3-4-8-7-6-5, starting from the front, passenger side of the engine and moving clockwise. The 4.6-liter's firing order is 1-3-7-2-6-5-4-8.
The 5.4-liter's cylinders are numbered 1-2-3-4-8-7-6-5, starting on front, passenger's side of the engine and moving clockwise around the engine. The 5.4-liter has a firing order of 1-3-7-2-6-5-4-8.
If the firing order is incorrect, it causes the sparks to go to the wrong cylinders. This means the engine will run rough, stall or backfire, if it runs at all.
