What is this vacuum connection

Discussion in 'Engine Performance + Maintenance' started by Hartwell, Aug 15, 2019.

Car Parts
  1. Hartwell

    Hartwell Newbie

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    I suspect this connection (yellow) may be one of the causes to my misfire/timing problems on my 7.4 burb. I didn’t notice it because there was no hose or anything. my question is, is there supposed to be a hose there and if so where does it lead? If not, do i plug it? I ran some vapor through what i believe is my vacuum advance hose (purple) and it came out here.

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  2. grampadirt

    grampadirt On MEDICARE Officially Old

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    That vacuum tube controls the cold idle,the ECM controls the spark advance.There is a tube that comes from the TBI to that little black box that controls when the thottle drops from fast idle to normal.Follow the small solid black plastic tube,it should go to a vacuum diaphragm on the TBI unit.Start the engine and let it warm up,after a few minutes you should see the diaphragm release dropping the idle.BTW,that little tube circled in yellow is a vent.All this works kind of like a fast idle choke on a carbed engine.
     
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