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While poking around top of the engine, I noticed a hose that did not lead anywhere:
Even though it was tight and dark there, I was able to trace the other end of the hose to the vacuum port on the distributor. Then, after consulting with the manual, I am thinking this is the vacuum hose that is supposed to be connected to the vacuum regulator (under the B bank), correct?
The problem is that the hose appears to be too short and it would not reach the vacuum regulator. I also checked (by feel, because there is very little room to operate there) that all three entry points on the vac regulator appear to be connected to vacuum hoses already. WTF?
Don't know how long it's been like that. Most likely since at least the time I got it. (Because I did not do anything in that area and did not try to reach the distributor yet.)
Does it mean I did not have vacuum to the distributor at all while driving/playing all this time? What are the consequences and symptoms of running without vacuum line connected to the distributor?
Here, I tried to take a better picture of the disconnected vacuum hose. It can be easily traced to the back of the distributor:
I checked the equivalent line in my '86 donor XJS. It exists, and it appears to go from the back of the distributor to this brown vacuum regulator:
But in '85, this brown vacuum regulator has two lines going out, with one of the two later split into two more. They connect to intake manifold (top and bottom) and one line goes all the way to the front to connect to (what I think is) vacuum dump valve.
So, there is not even a room/place to connect the vacuum line from the distributor! Where the heck is it supposed to connect to in '85?
The problem is that the hose appears to be too short and it would not reach the vacuum regulator.
At one point in its life it was longer. That plastic nipple is a coupler to join two pieces of vacuum hose together, possibly two different diameters....an annoying Jaguar habit, I might add.
As to where it's supposed to go....I'm not sure.
Sometimes the illustrations in the parts catalog are helpful.
Are both the hoses for the distributor vent system present and accounted for? One to the top of the dist cap and the other from the side? if not, perhaps that's where your mystery hose goes?
Yes! I believe it hose #2 in the first link. But it is supposed to end in a T-connector, to hook up to another hose, and together to the vacuum regulator.
Mine is too short to reach anything, and it does not have a T-connector at the end. Somebody was improvising?
What are the symptoms/consequences of running without vacuum line connected to the vacuum capsule on the back of distributor?
While poking around top of the engine, I noticed a hose that did not lead anywhere:
Even though it was tight and dark there, I was able to trace the other end of the hose to the vacuum port on the distributor.
Exactly where on the distributor was the end of the hose connected to? The vacuum capsule or the distributor cap?
If the vacuum capsule, the symptoms are poor fuel consumption and an unresponsive engine. It is HIGHLY likely that the vacuum capsule itself has failed too.
The best thing to do, IMO and experience, is to ditch all those tiny tubes and gizmos, and just connect the vac capsule directly to the small spigot under the A bank throttle body.
Greg
Last edited by Greg in France; 08-21-2017 at 02:31 AM.
Exactly where on the distributor was the end of the hose connected to? The vacuum capsule or the distributor cap?
If the vacuum capsule, the symptoms are poor fuel consumption and an unresponsive engine. It is HIGHLY likely that the vacuum capsule itself has failed too.
The best thing to do, IMO and experience, is to ditch all those tiny tubes and gizmos, and just connect the vac capsule directly to the small spigot under the A bank throttle body.
Greg
Yes, the other end of the hose is connected to the vacuum capsule on the back of the distributor.
Connect it under Bank A throttle body? Not at bank B where most of vacuum lines are congregated and how it is shown in the diagram?
Is the idea that "vacuum is vacuum" and it does not matter where it comes from? But what about all those gizmos like vacuum regulator, vacuum dump valve, etc. They are not much needed?
Yes, the other end of the hose is connected to the vacuum capsule on the back of the distributor.
Connect it under Bank A throttle body? Not at bank B where most of vacuum lines are congregated and how it is shown in the diagram?
Is the idea that "vacuum is vacuum" and it does not matter where it comes from? But what about all those gizmos like vacuum regulator, vacuum dump valve, etc. They are not much needed?
Just for clarity, A bank is the US passenger side. And no, they are not needed. As you say vac is vac, and the spigot under the A bank TB is handy for the vac capsule. But put a vac tube on the capsule and suck. If it does not hold vac the capsule is toast.
The vac lines that power the cruise control bellows stay, of course.
Is the idea that "vacuum is vacuum" and it does not matter where it comes from?
No.
It matters where it comes from.
You have direct or constant manifold vacuum and then you have (what is often referred to as) "Ported Vacuum". Direct or constant vacuum will come from the nipples (for instance) at the rear of the inlet manifold or any nipple downstream of the throttle blade.
Ported vacuum will come from a nipple on the upstream side of the throttle blade so that vacuum is supplied only as the throttle is opened. Typically ported vacuum is used for distributor vacuum advance because you don't want vacuum advance at idle.
But what about all those gizmos like vacuum regulator, vacuum dump valve, etc. They are not much needed?
All part of a complex scheme to avoid pinging, heat the cat converters more quickly, and stabilize idle quality. It's a bit of a brain tease to figure out out it works.....when all the gizmos are actually still operational. Many of us bypass all that stuff.
Thank you for the link! Extremely useful and helpful! With the details and rationale provided in the article, there is now a fighting chance I can understand what is going on with vacuum system one day!
So, I compared the vacuum lines in both '85 and '86 against the design described. Surprisingly, neither of them appear to be up to specs!
In '85, the issue is obviously that the hose coming from vacuum capsule was disconnected from the rest of vacuum system. Why? By whom? Who knows
In '86, the lines from dump valve appear to be messed up. Connected to places completely different from where they are supposed to go. WTF?
Is it normal for people to play with vacuum lines like that?
Surprisingly, both cars appear to take this "fiddling" in stride-- both run without too much fuss! Go figure
After studying the vacuum system design carefully (while re-reading relevant parts of the article multiple times), I was able to connect the orphan vacuum hose from vacuum capsule to its rightful place. (It goes to a T-connector under the RHS manifold, near the vacuum regulator.) I also fixed other vacuum lines accordingly.
I hope it is not a placebo effect, but I think the response improved. Also, I think that properly reconnecting the vacuum line to the vacuum capsule finally fixed slight hesitation/"mini backfiring" at slow speeds I reported on earlier (knock on wood/fingers crossed.) Cool! And thanks!
Other thing I would do it lift the distributor cap and use a hand vacuum pump see if the advance plate is actually rotating when vacuum is applied. I had one that was gummed up and didn't move, even though it was getting vacuum.
Other thing I would do it lift the distributor cap and use a hand vacuum pump see if the advance plate is actually rotating when vacuum is applied. I had one that was gummed up and didn't move, even though it was getting vacuum.
Good detective work though!
I am sure I will get to performing that test one day. But first I will need to add a hand vacuum pump to my tool kit!
Just suck on the vac tube that comes from the capsule, but on a doirect tube with no other gizmos branched from it. It will either suck freely (capsule toast) or not (capsule OK). I shall be very surprised if it is OK, but you never know. If it is NOT ok, then you are losing substantial performance and economy. This is a very important part of the system.
Just suck on the vac tube that comes from the capsule, but on a doirect tube with no other gizmos branched from it. It will either suck freely (capsule toast) or not (capsule OK). I shall be very surprised if it is OK, but you never know. If it is NOT ok, then you are losing substantial performance and economy. This is a very important part of the system.
Got it. Will definitely do this test later this week when I get to my garage. Thanks!
08-20-2017, 02:40 PM
Disconnected vacuum line? To distributor???
Somebody was improvising?
