The water pump in my 78 f150 went out the other day so I had to replace it. As I was putting it back together I came across a 3 port vaccum connector with no home. It appears to me there may be a pressure switch missing from the drivers side of the thermostat housing. I have googled, searched here, checked my haynes manual, and I cant find any info. Please see the attached photo. Its a 400 with air conditioning, non catalyst and vaccum hoses everywhere. I started it up and cant feel any vaccum at that port. I would like to straighten it out because it actually tees off there and goes to the vaccum advance on the distributor. Can anybody confirm my suspicions? It appears as if the PO removed it and plugged it. Any help is greatly appreciated.

 

A/T or M/T ?

 

from my memory witch is questionable the vacuum ran to that switch and then to the distributor , i think it was one of those emission things . when it got hot it would open up to let vacuum through ! if i remember right ??

 

That is the VCV youare thinking of. that heated vacuum switch is located on the T-stat housing and shown in the photo

If it is a A/T the OP needs a 7-74-R10 vaccuum diagram

 

I got a 79 f150 with a 400, a/t with the same thing going on. I have three hoses coming off that connection that go nowhere, best solution I've come across yet is plugging the lines, seems to make the truck run better. I also had an open line coming off the passenger side of the exhaust manifold ( hot gas recirculation, emission thing about 2" diameter that I covered with a beer can to keep from gassing out the cab of the truck) that I believe may have something to do with at least a couple of the dead-end vacuum lines.

It'd be great to find out for sure where those lines are supposed to go though.. Maybe they'll double gas mileage when hooked up

 

I got ahold of Mil1ion and after he saw the photo, he told me another VCV is supposed to be screwed into the side of the T-stat housing and those open hoses go on it like the other ones .
Remove the bolt plug and screw in an VCV number 8A564
He has a illustration of it on his web site.

 

there is no reason to run that thing. You should pull it and plug it off...no smog shop on this planet would ever realize it's gone.

the sole purpose was to hold back vacuum until the engine was warm, hence keeping your timing retarded until the engine warmed up...IMO unless building a concourse correct show truck, leave it off and just plug the vacuum advance straight into the bottom port at the base of the carb front/pass side...and if it's a dual vaccum advance dist, leave the port closest to the dist blocked off or replace the can with a single advance style. It'll never have any effect on functional smog tests, because you don't smog your engine when it's cold.

 

Thanks steponit, I hoped you would see my post and offer yours and Mil1ion's advice. What is that website? Also, I agree that most of that vaccum junk can go, especially here in Minnesota where i dont have to get it smog tested. I am merely trying to decide what can go and what cant. I had already debated eliminating a bunch of the vaccum lines, but am not sure which ones I can get by with yet.

 

How would I know if its a dual advance? Two lines? There is only one line and one canister I believe.

 

the distributor would have two advance units coming off, one stacked on another vs the traditional type with just the one unit. However, block off the back unit and it works the same. I "think" the rear most unit was used to actually retard the timing under certain circumstances.


this is the actual unit with dual nipples, but one canister

 

That is not a dual advance distributor

That is an Combo "Advance-Retard" dist.

 

Ok, so I need some more help with this. First off, when I consulted my local O'reilys, they said there are 4 different VCV's, and they are listed by color. Secondly, does anybody have a picture of the other distributor available for the 400/c6 for 78? Mine has a hole where that second nipple is. No nipple, and if the nipple is missing I have absolutely no idea where the vacumm line is either.

 

two dist's exist....one with 2 nipples, one with one...I got that picture from autozone.com...go there and put yo8ur info in and look at it there

 

That site is pretty awesome. I didnt know about it before...thanks for the tip!

 

hopefully you're not being sarcastic? I actually do find it very helpful when I need to see pictures of oem parts...they even have a database with a lot of diagrams, wiring etc