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vacuum switch port identification

Discussion in 'The Garage' started by Big GMC truck, Jan 15, 2006.

  1. Big GMC truck

    Big GMC truck Registered Member

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    Question regarding the vacuum switch found in the thermostat housing on a 1984 GMC K1500 305: The switch has 4 ports labeled M, HV, 2, and 1. What do these letters stand for? I think the ports hook up to manifold vacuum, vacuum advance, and heat riser. Thanks
     
  2. Big GMC truck

    Big GMC truck Registered Member

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  3. JIM88K5

    JIM88K5 1/2 ton status

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    Have you looked at the emission label ?
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    The decal on the radiator support is the only place I've seen the "letters" and numbers ID'd,and tell where each vacuum hose hooks too..no book I've seen has a breakdown of them,and I have quite a few GM tech books and parts catalogs,maybe you can get vacuum hose diagrams from Chiltons and other sources by special order too,or perhaps at yout library..I found one Chiltons book for vacuum diagrams at a town library about 5 miles away that has saved my butt many times.but it can only be used at the library..though you can make copies of the pages needed..

    I sometimes luck out and find a truck in the boneyard the right year and engine with an intact emission hose routing decal..we used to get calls at the junkyard from people wanting to copy the diagrams on many 70's cars,there was so much "spagetti" under the hoods those years!..some collectors far away had us take a close up photo of it,and mail it to them,and they would send us some cash in return..

    In my experience,the PVS (ported vaccuum switch) in the thermostst housing is for the EFE Valve (heat riser),and some have 2 other ports that go the the distributor vacuum advance...the other PVS located in the intake manifold usually runs the EGR valve,but I've seen some with 4 ports,and couldn't say for sure what the other 2 ports are for,but I think they also control the spark advance possibly...plus if your in california,everything is different there emission-wise,as far as how everything is plumbed up,or what is used ..:doah:

    I liked the 50's best!..NO emissions!--and NO confusion about where to plug all those hoses onto...?:crazy:
     

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