I had a misfire problem not long ago on my '97 Deville and the first step was to replace the plugs. At 92K all the platinum tips were gone. Well, my wifes '96 Bonneville 3800 series II (N/A) was running rough and at 112K I figured it was time. The manual calls for 41-601'*, but I found platinum tipped 41-921'* in there. When I bought the new plugs they (A/C Delco, dealer & parts stores) now call for 41-101 "Iridium" (I don't know what the difference between platinum and iridium is), which is what I bought. Interestingly enough, unlike the Northstar, when I pulled the plugs, all the platinum tips where there. In hind site all I needed to do was clean, regap and reinstall them and I'm sure they would ahve been good for another 100K. They were in such good shape I did, clean, regap and saved them, "just incase". Comments?

One other interesting note. I noticed that the A/C Delco box said "Made in Japan" :o

Even the throttle body says made in Japan (on my car anyway) but ahh whatever. The spark plug thing is something I wouldnt have done just because thats me and I like things to be perfect and brand new but I hope it works out for you as it seems like it has.

NGK makes the AC Delco plugs. Either brand is favored for us.

Platinum is fine in the non-supercharged cars as well as Irridium or copper, but plain copper plugs or Irridiums are for the Supercharged cars. Platinums don't do well in forced-induction applications.

Read the Techinfo article on plugs

I put bosch platinums in my 97 se...its starting to develop a miss at certain speeds...I've heard a mechanic say that because gm uses a higher voltage spark then other manufacturers...that the tip of the platinum plug will decay rapidly...i will have to pull one of mine to check....

What do signs of a misfire consist of?

Test a misfire at light throttle climbing a hill. You'll feel it.

Bosch plugs have been a nightmare in every GM vehicle I've owned. Bosch O2 sensors as well.

Pull a plug wire and drive it on 5 cylinders and you'll know.

Have Bosch platinums in both my cars with no problems to date.
Sorry I have to chime in here.
SSE 34,000 on them
SE 5,000 on them.
I also have the stock ignition systems. I'll let you know if and when they fail.

So if they were going to fail I would think it would show up in my SE first with
the Delco ignition and hotter spark.
Put NGK'* in the Supra, WOW what a difference from the Denso plug.
I plan to upgrade my SSE to the Delco next time I go wrecking.

Mine started to miss at around 10,000 miles...it misses under lite acceleration at around 35 to 40 mph....otherwise it runs great.......still gotta pull a plug....the electrodes are very small on bosch platinums to begin with....platinum is very expensive! lol