Just bought a 1987 Blazer with a 350TBI. After basic tune-up stuff, it runs pretty well, but there's a noise it's making that has me worried. It only happens under heavy acceleration, and sounds like a kid with a marble in a tin can is shaking it, like something is loose and flopping around - maybe a rocker arm? It doesn't have a real rhythm, as far as "tick tick tick", as it's more like "rattle................rattlerattlerattle......... .................rattle rattle" (if that makes any sense at all).

The engine idles and accelerates fine, just making that noise that has me worried.

 

sounds like valve rattle. There is probably a lot of carbon built up in the cylinders. Higher octane gas and or run some seafoam through the TB to clean it out.

 

I've run Seafoam through once, but I'll try again and see what happens. Any other fixes for that?

 

reving it up and trickling water in the TB will break loose carbon as well as tranny fluid the same way. If you put a tank of 93 in it and it stops you'll know what the problem is then.

 

How about timing that's too advanced?

 

I'll try running some Seafoam through the TB while the truck is running, and I'll put another can through the brake booster line.