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The best stuff I've found thus far is gunk heavy duty gel. Took baked on inch thick grease on my trans right off. Whatever you do don't get it in the intake and if it's a long block but still on a stand don't get it in any of the exhaust ports
Cover the alternator, distributor cap, and air intake with plastic bags. Per the owners manual, those are the 3 main things that need to be protected while cleaning the engine.
Get the engine hot before you spray it down w/the GUNK. The longer you leave it on there the better it will do. The really stubborn stuff will require a brush and some scrubbing. I don't cover anything with bags BTW.
Remove the PCM Computer plug and put fresh dielectric grease in it. Put the plug back on and then try not to get any water in the area of the PCM Computer plug.
Others have not done this and had to replace the PCM Computer after bay cleaning. As the PCM Computer put smoke in the cab after trying to starting it back up.