454 Tuneup Problems

I have a 1985 Southwind Motrohome with a gas 454.
I have had ignition problems with it since I got (reason previous owner sold it).
I traced the original problem to corrosion on the #5 spark plug boot when
it fell off in my hand.
Since then I replaced the wires and plugs with some Bosch Platinum. It ran so good I had problems keeping it under 70.
Then all of a I started loosing power. i was able to make it home, but I was not running on all 8.
I pulled the plugs and found that 3 had suffered from Splash Deposits (first time I had seeen that)
Before I put another set of plugs in,doeas anyone have any advice?
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Yes, use ANYTHING but Bosch plugs. They're garbage. If you want platinum, go with AC Delco platinum. If you're looking for a good non-plat plug go with AC Delco Rapidfire.
Doc

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I don't need the platinums and the troubleshooter in me says to use the same type that I pulled out so i can re-establish the previous baseline.
I will then use a cumbustion chamber cleaning fluid to get rid of the build up on the pistons which is what Bosch is saying is casuing the problem.
Their explanation makes sense though. "first tune up in over 10 years and the engine has been operating at low performance. This has caused deposits to build up and now that new plugs have been istalled, the deposits are cominf off and sticking to the hot insulator on their way out the exhaust port."
I will also check the timing once I figure out how since I can't even get to the fron of the engine.
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