I've got an '84 f250. Does anybody know if the vacuum control valve (vcv) on the thermostat housing is supposed to supply vac to the dist vac adv all the time? This is the center port on a three port switch.
According to the vac diagram there is a single vac line that comes from the intake vac port near the temp sensor. It then "Y's" with one leg supplying the lower of the three ports on the vcv and the other supplying the upper port after going through a vac restrictor. The center port goes to the vac adv.
The concern here is vac being supplied to the vac adv at idle.
Normally this would go against common practice.
This is an orig. owner truck and everything is stock.

 

Those valves were to supply vacumn to the vacumn advance port of the distributor when the water temp got too high. Normally (cold), they do not supply any vacumn.

As I recall, (screwed around with many of them, been a while!) The idea is to speed up the engine by advancing the timing to circulate water faster through the engine. The only time it functions that way is at idle, rest of the time, underway, the engine is turning faster, and that function isnt needed. In the day (still) of idiot lights, you dont know what the water temp is until its too late. With the vacumn valve, some relief is provided when temps get too hot.
Also was necessary when carb vacumn to dist was changed from manifold vacumn to ported vacumn or spark port vacumn. That is, no vacumn to dist advance port until slightly off idle of butterflies.
LOL-- maybe someone will chime in that is a little clearer

 

Incorrect. The valve is fed manifold vacuum and the port vacuum from the carb. Between cold and normal operating temp the ported vacuum from the carb is fed to the vacuum advance unit. When engine gets too warm from idling too much in traffic, the valve switches to the manifold vacuum to increase the idle speed for additional cooling. When engine cools down to normal temp the valve switches back to the ported vacuum to increase fuel economy.

 

Sorry, but I think your both wrong. That ported vacuum switch activates as the engine is warming up, I don't recall the temp stamped on that device but it is lower than the normal operating temp. When that designated temp is reached, vacuum to the dist advance cannister is switched from partial to full vacuum. If you look at one of the hoses from the intake manifold to that ported switch, there is a small in-line plastic restrictor....I believe it was done to lower emissions during warm up. On mine, I removed the restrictor because it runs and idles better during warm up. Now, there IS a hot idle compensator on the hose from the PCV valve. When under hood temps get high, it opens and allows air in, supposedly to increase the idle speed and / or smooth it out....I think thats where the confusion is......hope this helps.

 

Bear 45/70----Thats what I just said . There are several designs of vacumn switches, but essentially function the same. Ported vacumn is no vacumn---at idle that is. Ported vacumn is drawn from a slot/port ABOVE the butterfly at idle, therefore no vacumn = no effect on the vacumn advance diaphram of the dist. The vacumn switch is temp controlled for higher water temp. Otherwise, why put it there. At speeds above idle, ported vacumn and manifold vacumn are the same. I dont believe it has anything to do with fuel economy because all other paramaters (idle speed, initial timing) are the same. Vacumn advance is an economy and streetability feature, that is why racers dont use it. it has nothing to do with the max engine power output.
beetle-- The vacumn switch does not create ported vacumn, that comes from the carb and could go straight to the dist, for its function, it dosnt need a switch. No vacumn through a temp controlled switch still = no vacumn! The little in-line plastic "cannisters" are either vacumn delay valves that are rated in vacumn time delays by the color of the canister, or rather 1/2 of the cannister. Another cannister is a one-way valve that passes/blocks vacumn depending on which way it is installed and also on whatever the strategy by the mfg for it is. I have played around with both valves trying to get a streetable, maximum timing curve. There is a lot more than meets the eye when trying to taylor all the advances for the street. I also dont think it has anything to do with emissions. Leaned out idle jets do, but not much else is done at idle for emissions, I could stand corrected on that. Hot idle compensators are just another strategy to speed up the engine at idle to increase cooling. There may be some overlap on methods, been a long time since I played around with vacumn. Its electronic now. BTW, looks like I may be spelling vacuum/vacumn wrong----never said I was real smart

 

That's the way my 1984 460 is plumbed and works just like I said. The choke on the carb takes care of fast idle for warmup. The is nothing on the PCV hose on the 1984 460.

 

Ported vacuum is not no vacuum. By definition ported vacuum is no vacuum(or almost none) at idle, but has vacuum off idle which increase with throttle opening unless you go to WOT. Don't explain how ported vacuum works, I know how it works but you seem rather confused. Ported vacuum is not no vacuum, you call it ported vacuum.

 

OK, forgot to mention mine is an '85 California model 460 so I'm sure the emissions system is different from other states. Mine is bone stock and nothing has been modified; I know 'cause I bought it new No ported vacuum for the dist advance can, strictly manifold vacuum. Not trying to dispute the issue, only reporting facts. Likewise, I've spent many hours chasing down problems relating to emissions system and have learned quite a bit including info from this thread.

 

bear 45/70--- Vacuum is spelled vacuum, by the "Word" spellcheck---I stand corrected, but then I caught it myself.
Why is it that some of you guys have to start loosely throwing around terms like "confused" etc. Are you capable of carrying on a discussion in which you disagree without that stuff? "Dont explain how ported vacuum works" ? I didnt, I simply stated how I thought it works and I still do. I have also spent many hours over the years tweeking distributors. If you disagree, simply state so. No I am not confused, but like you have my own opinion.

Ported vacuum is for the purpose it was designed, NO VACUUM. Once the butterflies open the port, then ported vacuum becomes the same value as manifold vacuum and that occurs within a very few degrees of butterfly opening. Ported vacuum does not increase as the butterflies do until WOT. Ventura vacuum does increase as the butterflies do. Been a while, but I believe that ventura vacuum is what is used to pull in the secondaries of most carbs, unless mechanical. At WOT, there is da** little vacuum of any kind! Anyone who has installed a newer ( thats the past 15 or better years!) carb has had to read which port to plug and which ones to use for the dist.

BTW, a lot of my time was spent on a 76 460 E250 Chateau Club Wagon that I towed a 31' travel trailer with. Confused? I dont think so, my stuff always worked. California autos probably have stuff I havnt dealt with so I can stand corrected on some issues. If you are dealing with 84 models, you are far out from the equiptment on ~76's. It was then and earlier that vacuum switches were installed. Even if I disagree, I will respect your opinions-----hope for the same.

 

Ported vacuum by definition is a source of vacuum that has no vacuum at idle but supplies a a progressive more vacuum as the throttle plates are opened until you get the same as vacuum as manifold vacuum. But never is ported vacuum called "no vacuum". I have only ever lived in the Peoples Republic of Kalifornia when required to be there on active duty in the 1960s. So as to Kalifornia equipped 460s I could careless. As to Ported vacuum, it's been on car engines since the 1950s but you obviously are unaware of what ported vacuum is for anywhen it came along. Oh yeah, I was spelling vacuum before you noticed girls. Why is it when you guys are totally misinformed or totally wrong you take offense when called on it?

 

The more you carry on, the more you agree with what I said. Read the post I did on ported vacuun again. Remember it was in response to the thread starter about the vacuum switch on the thermostat housing. I also never called ported vacuum "no vacuum" that term is only the effect. Guess I should have dumbed down that statement.
I was specific, at idle ported vacuum is no vacuum, but only at idle (thats what I said and understand). When the butterflies open, just a few degrees, the port becomes part of the same vacuum chamber that has manifold vacuum. The vacuum advance of the dist reacts by applying its full advance to the dist, causing it to advance. That is unless you have cranked the screw (if it has one) so over 20 # of vacuum is required. Ported vacuum might be slightly progressive while the butterflies move across (very few degrees) the carb opening, but once cleared, its manifold vacuum.
I do care about california vehicles, not because I ever owned one, but recognize that posters with them, should be responded to with help with a disclaimer. Read again, I acknowledged that.
Your old age is not serving you very well. (we are apparently both somewhat older farts). Your old age has caused you to think you have ESP. Unless my 1st grade teacher, eons ago, has been talking, you have no idea of when I noticed girls.
Nope, I have not taken offense, at my ripe old age, I simply account for other ignorant old farts.
You have not proven differently anything I said about ported vacuum, looks to me like you confirm.
The thread started may not care about our diatribe on vacuum, he only inquired about a simple switch. I have given one opinion, you another. I suggest he ask further, maybe an expert will respond. Meantime, you and I have about run out of meaningful discussion.

 

IATSE44---Sorry about all the confusion. I found my old (updated print 1994) book on Holly carbs. Dont know if you have a holly or a motorcraft, but the principles are the same.

I didnt pull my previous statements out of some hat, there was a basis in fact. This holly book is an interesting read. Lots and lots of stuff on carbs, economy and performance plus emissions. Also many variables and strategies for emissions that changed over the years.

In a previous statement, I said that I didnt think that the valve you referenced had anything to do with emissions, incorrect . It provides application of ported vacuum (sometimes called spark port vacuum), which is = to ~ 0 HG. I call that "no vacuum". That is an emission principle that retarded timing advance at idle effectively richens the mixture and loweres the combustion temp and "---dramatically lowers HC and NOx emissions". Full vacuum advance at idle would certainly give better combustion, hotter, better performance and driveability, but emissions go to HE--. Guess which way the EPA chose---! I will be glad to send you a scan of the page (112).

On page 111 a partial quote is "----A temperature-sensitive valve allowed spark advance if the engine started to overheat and during cold operation". I believe thats exactly what I said the valve was for except I did not include the cold function. I wasnt 100% accurate, but I was not wrong either. That is common for all us non-experts.

Another defining quote on pg 112 is "---Carburetors equipped with timed spark advance (no advance at closed throttle) have a port in the throttle bore. This port is exposed to vacuum as the throttle plate moves past the port---usually slightly off-idle" The valve you are requesting info on provides the control function for applying both types of vacuum to the distributor vacuum advance mechanism. There may numerous Y's, plastic cannisters etc. in the vacuum path to the dist, but the basic function of the valve is the same. But then I believe I said that.

I suggest you pick out the truth for all these opinions (mine included) coupled with others and you will have a pretty good picture of the valves exact function. LOL

 

Thanks benshere...I was able to figure it out with the info you guys supplied ( looking closer at the vac diagram. I would very much like to see a scan of those pages.

 

IATSE44--PM me for some #'s