Engine Runs Rough After Customer Does Tuneup
Does this sound familiar? The customer tunes up his own engine. He replaces the spark plugs, spark plug wires and ignition coil, and now the engine has a bad miss at idle or off idle. He brings it to you and you find it has good spark and injector pulse on all cylinders, yet the engine runs bad. One of our hotline callers recently dealt with this situation on a 2000 Ford Ranger with a 3.0 liter engine.
One of the things we see often is that the spark plug firing order is wrong, especially if the customer works on his own vehicle. It is easy to plug the wires into the coil pack wrong. On the connector side of the coil pack, the wires plug in 1, 2 and 3, front to back. But on the opposite side of the coil pack, the wires should be 5, 6 and 4, front to back. It is common for the wires to be plugged in wrong, typically 4, 5 and 6, front to back or some other combination. This engine has a waste spark system so it has companion cylinders that share the same coil trigger.
On six-cylinder engines, 1 and 5; 2 and 6; and 3 and 4 are companion cylinders. I had the technician verify the firing order, and in this case, the wires were plugged in correctly.
Next, I asked the technician to check the coil connector. He noted that the coil connector was a four-terminal horizontal connector. Ford makes two types of ignition coil packs. One style has a horizontal connector, and the other style has a vertical connector. These coils are not wired the same internally, but they use the same style connector so the wrong coil can be mistakenly installed on the engine. In this case, the customer had installed the wrong ignition coil, causing the engine to miss because the firing order was not correct. The 3.0 liter engine requires a vertical-style coil connector and the 4.0 liter engine requires a horizontal-style connector. The correct coil was installed and the problem was fixed.
Note: Starting in 2001, Ford changed the coil connectors to eliminate the wrong coil being installed, but on model years 2000 and older, the horizontal or vertical style coils both fit any engine.
The illustrations show both style of connectors.
Vertical Connector Six Tower Coil Pack for 2.5L Contour/Mystique, 2.5L Cougar, 3.0L Taurus/Sable, Windstar, 3.8L Mustang and 3.0L Ranger, 4.2L E/F Series
Horizontal Connector Six Tower Coil Pack for 4.0L Ranger, 4.0L Explorer and 4.0L SOHC Explorer/Mountaineer
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