 Ford discovered a calibration error on the block boring machine that ended up over boring the early 5.4L engines for all of '97 and half of '98.   This was discovered (especially up north)  when many fleet trucks with this new modular engine began to knock like a rod bearing going out during cold weather start-up after approximately 85,000 miles. After engine warm up or in warm weather (well above freezing temperature) the knock subsides (metals expand in heat). Apparently, according to the tech bulletin issued in late '98-'99, the cylinders in the 5.4 L's  we're accidentally over bored causing piston slap when cold during startup, and stated it would not harm the engine or interfere with function or performance. After purchasing a 35,000 lariat 4x4, I found the news disappointing at best and little consolation for owners that have to listen to an annoying knock in the engine until warm-up of the engine or warm weather (which ever comes first). Mine has over 160,000 miles as of this note date, and has not burned oil, but simply irritates me that Ford would not do anything about it (expense of putting oversized pistons in these engines to cure the issue). WARNING: AVOID the 5.4L engine in the '97 and most of the '98 Ford vehicles at all cost. Beyond that they're good engines!