Whatcha reckon guys ,, GM spent a whole bunch of research time and money deciding that the engine worked best at certain temperatures , and having the intake charge operating within a given temperature range . So they made a manifold heat riser device .
If the heat riser is stuck open then the engine will get too hot a fuel charge once the engine is warmed up , this can cause various performance faults , eg. detonation , pinking , lean running .
If it is stuck closed the fuel mix is not heated and poor cold running performance is experienced , excessive use of the choke is needed , etc ,etc .
The manifold heat riser on my truck has 2 springs on it , one is much shorter than the other ( less coils, and wound the oposite way ) These 2 springs oppose each other and stop the riser rattling , The longest spring does all the work of opening or closing the riser valve and works fine , the engine performs fine all year round .
There is probably a bit in your truck manual showing how to set it all up , there is in mine .
