My 89 Toyota pick up was running great right after I had made new keys for it and it had sat for 2 weeks before I drove it again, I let it warm up awile since it sat for a little while and drove it drove home great. Then I came to town and the engine began to bog down and sounded like it was missing and then I heard the rod knock only when barely touching the acceleration. Now it will not start and has when it turns over black smoke comes from the exhaust. I checked underneath and noticed oil by the rear main seal but that was all I could find wrong. What else should I do, I thought maybe the rod bearings maybe bad also but not sure?
The knock makes me believe something made its way into a cylinder. Remove the plugs and check to see if they are all black or only one or two. You may have a bad head gasket and the engine my have been knocking due to hydrostatic lock from coolant, or the fuel pressure regulator may not be working properly allowing too much fuel to get into the engine causing the black smoke and the knock. Check fuel pressure to confirm that.