The Ford F-150 remained a relatively simple machine that didn’t even see the benefit of fuel injection until 1987; but starting in the late 1990s, Ford went on an electronic control craze. One system in particular has given F-150 owners headaches since its release: the coil-on-plug ignition system. Ford designed this system to give the pickup more power, while lowering emissions and fuel consumption. It also added a new problem: the notorious “Cylinder X Misfire” code. This system has eight coil packs in total, so isolating the failed ignition coil on the 5.4-liter engine may be a little tricky.
Plug the OBD-II scanner into the data link connector on the lower driver’s side of the dashboard. Turn the truck’s ignition to the “Run” position, but don’t start the ignition. Begin the scanner’s scan function and observe as it connects to the truck’s computer system.
Read the codes displayed on the OBD-II scanner. The scanner will describe one code as “Misfire Cylinder No. X,” with the “X” representing the cylinder number that has a firing problem, if it is a single misfire. A “Multiple Cylinder Misfire” code means there is a problem other than a single coil pack.
Compare the cylinder number listed on the scanner with the layout of the F-150s engine. Ford numbered the cylinders 1-2-3-4-8-7-6-5, starting from the front passenger’s side of the engine and moving clockwise around the engine. This identifies which coil requires testing.
Verify the coil pack wiring harness is plugged in. If the harness is not plugged in, say “duh,” slap your forehead with your palm, plug it in and recheck the operation of the F-150. If the harness is plugged in or continues to have a misfire after plugging it in, proceed with the testing process.
Pry upward on the passenger's side door scuff panel with a flat-head screwdriver to disengage its retaining clips, then remove the panel. Open the fuse panel door on the passenger’s side kick panel by opening it until it’s perpendicular to the kick panel, then pulling its curved tabs from the kick panel. Pry outward on the center pin on the pin-type clip on the top corner of the kick panel with a flat-head screwdriver, then pry the clip from the kick panel. Remove the kick panel.
Remove the two screws securing the inertia switch using a ratchet and socket, and pull the inertia switch away from its mount until you can access its wiring harness. Pry upward on the locking tab on the inertia switch’s wiring harness, then unplug the harness.
Start the engine and allow it to stall. This eliminates all fuel from the lines, not allowing the truck to start during the testing process.
Unplug the wiring harness from the inoperative coil pack and look at it with the locking tab facing down; the pin on your left is the “Ign Start/Run” pin and the one on your right is the “COP” pin. Look at the powertrain control module located under the hood and notice there are three wiring harnesses plugged into it. The harness on the driver’s side of the truck is the engine harness. The engine has four rows of wires. The wires harness closest to the top consists of pins 1 through 17, from right to left. The second row down houses pins 18 through 33, from right to left. The third row down contains, from right to left, pins 34 through 50. The final row of wires on the harness houses pins 51 through 66, from right to left.
Determine the pin on the PCM that matches up with the coil pack you are working on. Cylinder 1 uses pin 17; cylinder 2 uses pin 11; cylinder 3 uses pin 12; cylinder 4 uses pin 14; cylinder 5 uses pin 10; cylinder 6 uses pin 15; cylinder 7 uses pin 16; and cylinder 8 uses pin 9
Touch one end of a non-powered test lamp to the “Ign Start/Run” pin in the coil pack’s wiring harness; contact the other end of the test lamp to the corresponding pin on the PCM for that coil pack, as determined in the previous step. You can stab the PCM wire with the sharp end of the test lamp or use a thin probe attachment on the end of the test lamp to make contact with the PCM pin inside the harness.
Crank the engine and watch for the test lamp to pulse continuously. If the test light consistently blinks, there is a pulse coming from the PCM to the coil pack, and you may proceed to the next step. If there is no blinking, or there is inconsistent blinking, the problem is in the wiring or powertrain control module, not the coil pack.
Turn the ignition to the “Off” position. Remove the bolt securing the coil using a ratchet and socket. Pull the coil off the engine with a slight twisting motion. Press one end of a spark tester inside the coil, like a spark plug would go. Press the other end of the tester onto the spark plug. Adjust the spark tester to a gap of between 0.040 and 0.050 inches. Instruct an assistant to crank the engine as you watch the spark in the tester. If the spark is a bluish white, the problem is in another system, such as fuel or air intake. If the spark is a red or orange color, the coil failed.
