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I have spent a few hours reading on the forum, but I haven't been able to find the answers specific to my situation. So, I am hoping one of you can help. I have a '78 F250 with a 460. I have been working through some ignition system issues (alternator wasn't charging the battery. Ended up being the wire between the starter and solenoid was bad right after the fusible link). Anyway, I noticed that I have what I think to be the Ported Vacuum Switch that has all three ports open.
(Note, the pic only shows 2 ports because of the angle I took it at. There is a third port in the middle of the other two, but offset towards the back of the engine.)
Any thoughts and where the hoses should runt to from the PVS, or can I just cap the ports?
Not sure if this will be much help to you, I'm sure others will chime in with more precise details.
On my 73, 390, I have a 3-port PVS in the same location on top of the thermostat housing like yours.
On mine, the ports are connected as follows:
Top: Connects to a small stub tube sticking out of the base of the (Holley 2-bbl) carb
Middle: Vacuum advance actuator on the distributor (your pic looks like your goes direct to the carb)
Bottom: Connected to a multi-port block I don't recognize just below the EGR valve (also connected to this block is the vacuum line from the brake booster)
The setup notthemaniusedtobe describes would be for switching the vacuum advance from ported to manifold vacuum if the truck overheats, in order to advance the timing a bit at idle, causing an increase in engine speed and thus water pump flow to cool the engine.
A 3-port PVS is designed to, at some temperature, switch which of the top/bottom ports feeds the middle one. (A 2-port PVS just switches on/off between the two). Exactly what this PVS would be used for depends on the calibration & emissions control setup on your truck. Switching distributor advance for overheat protection is a good possibility, but there are also others (controlling a heat riser valve in the exhaust, etc.).
Given that nothing's hooked up to it, it won't hurt anything as-is: it's just acting as a plug in your coolant fitting. You can just ignore it if you don't have anything you need to hook up to it.
I have a follow-up question:
My truck does overheat when the weather is warm if I let it idle for more than a minute or two. But, it is also missing the fan shroud. Would re-routing the hoses as notthemaniusedtobe describes above help with that? Or would adding a shroud be more useful?
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