Okay so this is where it all started about two weeks ago I bought my dream truck. The 1992 Chevy K1500 2dr Blazer 350 V8 5.7L L05.

I drove it home for a good 2and a half hour drive. I fell in love immediately it ran perfect the whole way.

3 days later I noticed that the oil was milky and the top of the intake manifold was horribly clogged with old oil and other gunk so I went and grabbed intake manifold gaskets because I removed the intake and the gaskets were done for. installed everything back as it should be made sure the rotor and cap were in place correctly with the wires double checked to the correct firing sequence and put new oil a filter and coolant in....

now this was the moment of truth I go to crank it up and it makes a really nasty grinding noise it act like it wants to kick over then the fan stops spinning it revs up like the engine is running when its not at all and the speedo is just sitting on 85 which is the highest point on there with no key in the ignition and if I turn the key to the on position it goes crazy jumping everywhere...I seriously need help on this thing the check engine light is on also.. this is my first time doing this by myself.. I really need to know where I went wrong

has this happened to someone else I don't want to blow a rod or piston

 

So the starter makes a grinding noise or the engine itself? The electric fan comes on right away, and the speedometer pegs as 85 with no key in the ignition. If the key is on, the speedo will bounce around?
All you did was intake manifold correct? It sounds like an electrical problem and maybe something is drawing down sensor voltage or else a bad ground which is causing your problems.
Just a guess but if you found an electrical diagram there might be something in common between the gauge and fan.

 

It sounds as if the grinding is coming from the engine.And does it matter where the main battery ground attaches to the front of the engine

 

Could it be the spark plugs it needs a major tune up