My recommendation is the recommended 0.050 plug gap. A wider gap may give a “hotter” (higher voltage) spark, but that is also higher stress on the coil insulation and can lead to early coil failure (they do fail). The gap of course also wears wider over the miles, so it’s important to replace them on a mileage schedule (I recommend 75k miles or earlier rather than the factory-recommended 100k miles - also reduces chance of plug binding up in the cylinder head threads - also use anti-seize sparingly on the spark plug threads - keep it away from the tip where it could vaporize onto the plug tip insulation, shorting out the plug).
It could very well be that many of the coil failures happen because plugs were either “over gapped” (on purpose or accidentally) or left in too long (worn electrodes => wide gaps), electrodes broken off (Bosch plugs) which gives huge gap and coil stress, or people messing around and temporarily firing the ignition with plug not installed or not grounded - also huge effective gap and coil stress, and plugs installed with low torque causing high resistance to ground also resulting in high voltage across the insulation and potential for arc-over.
The coil has the capability of putting out *way* more voltage than the insulation can handle. When the spark plug fires, it shorts the coil output to engine ground, limiting the actual peak voltage to that point in the rise of the coil output at which the gap fires. Wider gap => higher voltage on the coil’s insulation. The first time the voltage arcs thru the insulation weakens that point in the insulation forever, making the arc-over threshold at that point in the insulation lower from that point on - it effectively punches a hole thru the insulation, creating a new easiest path to ground. Any subsequent arcing thru that point makes the hole bigger and also creates a carbonized (conductive) track (path to ground) from the charred insulation material.
Go ahead and over-gap your plugs if you want to totally wreck your life (just kidding). Seriously - do it if you want. Just make an informed decision and be aware that you’re increasing the chances of coil failure over time if you do. Replace or re-gap earlier (maybe 50k miles) if you do because the gap grows further as the electrodes wear.
EDIT: I just looked it up in the FSM. Plug gap spec. is 0.048-0.053”. I target to 0.050, if I’m just under, I leave it. If a little over, I tweak it down until I’m at 0.050 or just below. Remember - the gap grows with miles.
'98 LXi - Later Concorde gages (black w/ chrome rings)/'99 LX - LHS gages (white) - HIR bulbs
Last edited by peva; 06-11-2019 at 08:03 AM.