Yeah, no matter what brand Iridium plug you use DO NOT GAP THEM, they come pre-gapped and attempting to do so will ruin the plug. AC-Delco plugs just work, its what the engineers designed the 4.2 to run on. Some of the after market plugs work ok, others will have you pulling them within a couple of weeks when they fail or foul. Haven't heard anyone use multi-tip plugs on the 4.2 and have success, so stick to a regular single electrode. If you don't want any issues, get ACD replacements....best $.02 worth of advice anybody on this forum can give you.
Bosch is poor quality!!!!!! I made the mistake of putting the Bosch platinum +4's on my '97 Trans Am years back and it ran great for about a week and got a CEL so I took it to my friends shop where he diagnosed mutiple misfires. Thought maybe the Optispark distributor went bad again(talk about a poor design):ugh: He instead pulled the plugs on the misfiring cylinders and it was 2 of the plugs had broken tips.
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