It's time to change plugs and I am rerouting the PCV vacuum line, heater hose lines and PCV heater lines on our 2003 5.4L to get more access to the plugs. Also, it's time to change the engine coolant, the heater bypass valve and all those spring clamps. I just did this same job on our 2002 6.8L and now have great access to the plugs on the passenger side. There are 2 differences that are interesting:
1. On the 6.8L the heater supply lines for the front and rear heaters are connected to the bypass valve. It uses a 3 port bypass valve - 1 IN/2 OUT. Both heater lines are closed by the valve. The 5.4L uses a single line valve which shuts off the front heater when the A/C is on. The rear heater line tees off the supply line before the bypass valve so hot coolant is always routed to the rear heater. While this may not be an issue for the rear A/C it just seems odd. When I reroute the lines I can tee off the rear heater after the bypass valve so the valve controls both lines. Anyone think of a reason not to do this? I never use the rear heater.
2. The PCV line on the 6.8L has a single line from the intake to the PCV valve. The 5.4L has a tee in the PCV line with one going from the aluminum throttle body housing and the other line going to the back of the intake in the plastic part below the aluminum throttle body housing. The line in the back has the larger rubber elbow that goes bad. I can't really see where the line goes, but feeling the plastic tube the elbow is attached to it goes to the plastic part of the intake. What is the purpose of the second line into the plastic part of the intake? I can't find a vacuum line diagram in the Workshop manual and there are only 2 places that "PCV" is even mentioned. The PCV line into the aluminum throttle body housing has the engine coolant heater fitting.

 

1. Moved the line for the rear heater to after the valve. The line now stays cool when the AC is on.
2. Still don't know why there are 2 connections from the PCV valve to the intake so I left it that way.
When rebuilding the lines I only used brass fittings and reinforced hoses.
Also, reworked the 1/4" PCV heater hoses and tied up some wiring.
Got everything installed and has been running for awhile now with no problems.