If a coil pac from a 4.6 will work on a 5.4 why not use a coil pac on a 5.4.

 

This is the main reason:

<title>Electronic Engine Control (EC) System</title><link href="VWA%7Eus%7Een%7Efile=VWAstyle.htm%7Egen%7Ere f.htm" type="text/css" rel="stylesheet">The Electronic Engine Control (Electronic EC) system provides optimum control of the engine and transmission through the enhanced capability of the powertrain control module (PCM). The Electronic EC system also has an on-board diagnostics monitoring system (On Board Diagnostics II) with features and functions to meet federal regulations on exhaust emissions.
The Electronic EC system has two major divisions: hardware and software. The hardware includes the powertrain control module (PCM), natural gas vehicle (NGV) module, constant control relay module (CCRM), variable load control module (VLCM), sensors, switches, actuators, solenoids, and interconnecting terminals. The software in the PCM provides the strategy control for outputs (engine hardware) based on the values of the inputs to the PCM. Electronic EC hardware and software are discussed in this section.
This section contains detailed descriptions of the operation of Electronic EC system input sensors and switches, output actuators, solenoids, relays and connector pins (including other power-ground signals).
The PCM receives information from a variety of sensor and switch inputs. Based on the strategy and calibration stored within the memory chip, the PCM generates the appropriate output. The system is designed to minimize emissions and optimize fuel economy and driveability. The software strategy controls the basic operation of the engine and transmission, provides the OBD II strategy, controls the malfunction indicator lamp (MIL), communicates to the scan tool [New Generation Star (NGS), etc.] via the data link connector (DLC), allows for Flash Electrically Erasable Programmable Read Only Memory (FEEPROM), provides idle air and fuel trim, and controls Failure Mode Effects Management (FMEM).

 

I assume you are wondering why '97 and '98 5.4L's have COP while the 4.6L's still had coil packs. I would assume that Ford knew they were going to be going to COP's on everything so they designed the 5.4L with them in mind and just kept the 4.6L the way it had been for the previous5 years since they would have also been designing PI heads by '97 and would go all COP's at that time. Also COP's are a far better ignition than coil packs.

 

COP's are annoying to remove that lil screw/bolt..

 

I don't necessarily agree with this..in most cases the COP system is better in terms of simplicity and reliability vs the waste-spark(packs and wires). But,there are situations where the waste-spark system is better.
JL