I found the vacuum hose for the distributor advance disconnected. where does it connect to? does it connect to a manifold vacuum source or a ported vacuum source. I looked at the vacuum hose connections in glorious technicolor by 'sarc' , I see the hose going to the distributor but not where it is connected to. Does it use manifold vacuum to keep it retarded at idle and advance as you accelerate? or does it use ported vacuum to keep it retarded at idle and advance the ignition as you accelerate? Doug knows the answer to this retarded question.
RETARDED

 

As I remember, it couples in on the inlet manifold near the throttle assembly, but I may be wrong.

Doug will know, he knows everything about Series 3s and even 2s or 1s !!!

 

As the years go by I'm afraid "Doug knows" is being replaced with "Doug knew"

The three-port vacuum distributor/vacuum valve (under the intake manifold) has one port to direct intact vacuum, one to the distributor vac advance unit, and one to ported vacuum. It serves as a vacuum delay valve as I recall.

Later tonight I'll dig thru my old notes.

Cheers
DD

 

of course Doug still has it right :-)

As I mentioned in the post, I moved the funny little three port vacuum thingy from under the inlet manifold where it was originally to the strut rail. I did this with the reasoning that if something decides to fall apart, I will now be able to easily see it. Where the valve was originally was crazy... anything could happen under the inlet manifold (like the hose falls off) and you wouldn't be able to see.

I highlighted the line in orange in the below pic....



The round metal looking canister attached to the strut rail is the three port vacuum thingy. The line coming out of it and going to the right of the picture is the distributor advance line. It is connected (obviously) to the port marked "dist" The line then drops down and disappears underneath the inlet manifold and goes straight to the vacuum advance port on the distributor

There is an excellent article here.... http://www.jag-lovers.org/xjlovers/info/XJ6Vacuum.pdf which explains how this valve works. (It is referred to as the "Distributor Vacuum Regulator" there)

 

Good diagram yes.

Saves me some rummaging

As I recall.....

Ported vacuum (from the throttle body) at the "carb" nipple much reach "x" amount before opening the valve so vacuum can reach the distibutor vac advance unit. I think it simply ensures no vac advance at idle.

In a situation where vacuum is very high but throttle is closed (coasting down with throttle closed) the valve switches again so that the vacuum advance gets direct manifold vaccum (from the "delay" nipple) but a restrictor in the doohickey limits it to 6.5"

I think.

I'll try to find out more and refresh my memory.

You might wanna open up the metal cap and check the diaphram. Often you'll find a split.

The "carb" and "delay" nomenclature is confusing and doesn't quite make sense in the application. I'm pretty sure the vacuum regulator was designed for an entirely different application and pressed into use on the Ser IIIs.




Yeah ! taht's it! That's what I meant. That's what I meant! :-)


Cheers
DD

 

Thank you 'SARC and DOUG' for the info. Now I have to find a new Distributor Vacuum Regulator or repair the old one if the diaphragm is still good. The nipple for the hose going to the distributor is broken. The other option will be to use the ported vacuum source off the throttle body to control the distributor advance and deal with the consequences thereafter, which I assume would be minor. Not sure yet. I have to take a look at how it is connected and decide. I am in the process of replacing all of my vacuum hoses so I will do the 'sarc' method and reroute the hidden hoses. Another issue re vacuum is when I accelerate with the AC 'on' I lose vacuum to the AC controller and the flap closes so I lose my AC momentarily. It seems as if the vacuum reservoir does not have enough vacuum to keep the flap at the middle vent open. I tested the vacuum reservoir and it holds vacuum so I am not too sure what is causing this. I am looking at installing an electrical vacuum pump,which I salvaged from one of my GM cars and use it only for my AC control and brake booster. Just something I am throwing out there to see what you guys think about the idea.

 

I posted the above before I read the post from "Milster" about the same AC problem on acceleration. Did not mean to duplicate stuff.

 

You wouldn't be the first






The consequences might be minor in a good way. Your car might like it, especially if your vac regulator is non-functioning and preventing *any* vacuum advance.

One possible negative consequence would result from emissions testing, if you're subject to it on your area. Even if you are in a testing-required area the vacuum regulator might not be an issue...depending on how stringent the requirements are, in your area, for an older model car.



Cheers
DD

 

@den

Glad you are making progress.

@Doug

I am planning to fit my new petronix distributor this weekend. I checked the timing and at 700rpm I am getting 24° BTDC, with the vacuum hose on. I think my 84 US spec car should be set to 17° BTDC, so even at idle I am getting 7° advance from somewhere...... I will recheck tomorrow with the hose off. I'm getting a bit confused with some other info I found that says once the car is warmed up at idle, there shouldn't be any vacuum on the line going to the distributor anyway, so it's not strictly necessary to take it off if the advance system is working properly ??

If the last statement is true, yet I am getting advance because I have vacuum at idle, I assume that means there's something wrong with my little valve thingy?? So I may end up going down the same route as den and going straight to ported vacuum, and have to deal with the SMOG consequences later. Just for my understanding, what is the likely relationship between lumpy idle and timing? Will being too far advanced help or hurt?

 

So....... I went and checked a few things...... When I take the line off the distributor I get 17° BDTC. When I measure the vacuum on the "dist" line coming from the 3 way valve its 19mmHg. When I measure the vacuum on the manifold, it's the same. The vacuum on the ported vacuum line just before the throttle plate is zero.

My conclusion from this is my 3 way valve is dead. For the moment, I have connected the distributor line to ported vacuum and removed the valve completely. Now, even with the the vacuum line on the distributor I am getting 17° BDTC.

I'll go for a drive tomorrow and confirm I haven't screwed anything up, then I'll switch over to the petronix and set the timing to 17° BDTC (with and without the vac line on)

 

@sarc,i am a bit confused by that also. in order to have the distributor advance while the engine is warming up, there has to be some sort of a thermal vacuum control. I have searched all over my car and found none. On the carbureted series 2, there is. On the series 3 I don't believe we don't have that option. Let's ask Doug. Nice thing for Florida and Cali is we do not have extreme cold so I am not concerned about the thermal control.
As far as the ported vacuum source for distributor advance control, it should work as designed if the diaphragm and return spring at the distributor is good and the port is not clogged. I will check my vacuum readings at the ported vacuum source from idle to 6000 RPM and post the results later today. P.S.On the GM carburetors we used to change the ported vacuum parameters by resizing the port. This is not an option there is only one ported vacuum source on the TB.

 

@den

Sounds good. We are both learning together. My cars "cold" start works really nicely although as you say, it's never really cold where we are. I know the EFI system richens up the mixture when the coolant is cold..... could that be in place of timing advance when cold on the carb series II cars? I'll be able to post back later today on my progress. Hopefully I can brave the current heatwave we are having here (it's over 100° already) and get on with things in the garage. The XJS needs an alternator also.... never a dull moment with old Jaguars :-)

 

Right!

No thermal control on the vac advance system.

Cheers
DD