I've got a relatively new rebuild on my 454. It was doing fine for a while, and then all the sudden developed what was a pretty serious surge. But there appears to have been a misfire in it.. it could have been a misfire all along. I just changed the coil-- and installed an electric fan (windstar). The problem was most noticeable at operating temp (210). Operating temp now is about 200. Between the coil and fan, the problem isn't anywhere near as big as before, but its still there.
I replaced the coil, and now the problem seems much less pronounced. but its certainly still there. It dosen't feel like as much of a surge, but rather a misfire.
I've looked for vacuum leaks. I've reset the idle mixture. Replaced coil, which helped some. replaced coil wire (only old wire, the plug wires are new.. could the wires be it?). Checked the timing. Inspected the distributor housing.
I want to track this down, because I can't really drive enthusiastically with this problem. Makes me too nervous. Trans fluid is fine (its so odd how even a slight low fluid problem makes my car wacky).
Where should I start to look now?
Ign is msd6AL, pro billet, blaster 3, new msd wires. Everything is about 6 years old except the cap, wires, and coil. Cap, wires and coil are brand new, cap and wires done on rebuild, coil just now.
I wonder why I only see accel stuff in the stores.. Not like there are *any* speed shops around here.
I'm short on ideas and don't know what to do. Any help is appreciated.

Matt

You don't say anything about plugs. I had a similar experience on my Vette BB. Would start and run fine, most of the time. Sometimes had what I thought was a 'lean surge' or miss. FINALLY figured out it was plugs. Even though it had 1 month old Rapidfires in it, I changed to Champion Platinum. NO MORE PROBLEM. I'm a believer now.

I'm running accel 574S plugs. They are shorty plugs and I use them because they fit and seem to be the right heat range. I don't know what other shorty plug to try?

Thanks.
Matt

They looked just fine from a plug reading standpoint when I checked them out when this problem started happening.

Could one or more of them just be not suitable or bad?

Matt