This one has me stumped so I thought I'd post here and see what people make of it.

My '86 XJ6, as purchased, had no refrigerant charge at all. Obviously, I made it through the winter alright and spring was OK but now that we're into the upper 80s where I live, it was time to throw some R134 at it. Being a GM lump, it didn't take anything to find the low-side port, connect up, measure the existing charge (0) and charge it (about 35psi still low, I know).

When I turn the temperature knob toward the lower digits, I get wonderfully cool air. But here's where things get weird.

I've had idle issues since I bought the car. I'm sure they're vacuum related at this point and have been systematically going through the vacuum system to track the issue down.

I think I'm on the right track as today was particularly warm and the plastic on my center dash outlets is pretty tired so in desperation to get the cold air out, I just pulled the assembly off until I got home. What I saw was the "big metal flap" nice and open while I was off the skinny pedal but as soon as I'd goose the throttle, it would start to close up. Am I wrong in thinking this is not acting like your run-of-the-mill vacuum leak? Part of my confusion is stemming from the fact that I'm now dealing with the crossover between Jag and Chev parts.

Anyone have any ideas?

 

Well, I reckon I may have answered my own question. My MityVac tells me I'm between 15 and 20 inHg (remember, I have that missfire/idle issue)... until I accelerate. I've recently determined that the exhaust was fabricated from a combination of the stock Jaguar tubing, catalyst included, and a few GM parts to fit it up to the stock tubing. I am now quite certain I'm looking at an exhaust obstruction.

 

As designed the system has two features to prevent this. Check to see if they are still present (and hooked up!) on your car.

First is the so-called "muffin tin" vacuum reservoir. It's normally tucked into the left fender, sort above and outboard of the power brake booster

Next is a one-way vacuum valve on the vacuum supply hose to the the climate control unit. You would normally find this inboard of, and slightly below, the battery....but with the V8 conversion, who knows?

Cheers
DD

 

Thanks Doug. I keep meaning to check the Res-o-Vac but always manage to forget to. Ironic since the hose I had tapped into for the vacuum measurement is the one that was capped off to delete the cruise bellows (not so far from the Res-o-Vac). I'll have to look up the one-way valve. As far as I can tell, there isn't one. The only "valve" still in my vacuum system is this bizarre little knob by the inlet manifold that was used as a joint in two lines and is essentially just bi-directional ball valve. Unless I want to lower the pressure in those lines or shut them off, it makes no difference.
With as much vacuum as is used in the climate control system, I would guess it could deplete the available vacuum but with it being so throttle dependent and the way the engine just falls totally on its face above 4K, I'm going to look hard at the catalyst as well (read: take my reciprocating saw to it and weld in a high-flow). I already have to fix a significant hole between the right resonator and silencer (the arch over the cage) so it doesn't really bother me to do a little extra cutting and welding. I just bought the welder so any excuse to fire it up, right?

Anyway, I'll take a more thorough look at the vac plumbing tomorrow evening if it's not so blisteringly hot and post back with my findings. If the Res-o-Vac has been taken out, clearly that's an issue.

 

My car did something like that when it was still DOHC powered. I was mystified. On it's last day in that configuration, the AC was doing just great!

As now powered, I kept the resevoir under the brake booster and the one way valve. But, I've never charged the AC, so I don't know. It seems to have retained it's low vacuum idiosyncrosy even though the LT1 pulls plenty of Hg's. That leaves me with three ideas, similar to DD's thinking. Leak in the lines and or resevoir or a bad one way valve. or perhaps plumbed backwards. Oh, and the two spigoys under the battery box. Gotta be plumbed in the right order!! Mebbe this year?

But, now preoccupied with new toy! Repowering an orphan TroyBilt chipper Shredder!!!

Carl

 

Just a quick update on my situation.
Firstly, the L05 350 doesn't leave a lot of room for tracing things back by the firewall. I'd almost rather be back digging around under the hood of my '77 XJS trying to find the seized piston... that was more fun (shouldn't have sold that car even if it was a basket case).

Anyway, I tracked the vacuum hoses as best I could see them and not only are they far more perished than I originally thought, the whole system is a mess. There is no one-way valve anywhere on the system (a major no-no as I understand Jag vac systems). The Res-o-Vac unit is still in place but simply connects to... well, pretty much itself and the bottom spigot on the firewall. There should be a tee in that line somewhere to supply vacuum, but there is not.

So that's where I sit. My under-bonnet is a vacuum nightmare and it looks like I'll be re-plumbing the whole thing to Jag-spec at some point in the near future. What fun!

 

@millster

It's been "vacuum hose/diagram day" today on the board :-)

See the following post........

https://www.jaguarforums.com/forum/x...icolour-97221/

In the first pic you can see the one way valve on the left of the picture (It's white and black)

In the last pic you see the bread tin reservoir tucked behind the brake booster

I also found the following resource very useful as a reference.

http://www.jag-lovers.org/xjlovers/info/XJ6Vacuum.pdf

 

Indeed it has, yeah? I think a huge thank you is owed to you for that post with the hoses actually laid out. It's a little different for us "lumpers" looking at it but it still helps heaps in addition to a diagram.

I think I fell prey to the pitfalls of communicating via text in a forum though and didn't make it very clear what I was saying in my last post.

What I was trying to convey is that between having seen your "technicolor" thread and having poured over that diagram for a while, I had determined that my vacuum situation is bleak, at best.

The Res-o-Vac (breadbox) in my car has a vac line connected to it. That vac line runs the width of the firewall (resting on the dizzy at one point which I'm sure has to be great for durability), drops down by the battery and connects to the spigot for the HVAC. Are you visualizing the problem I am? The tee that connects the HVAC system to manifold vacuum is on the water valve side and lacks a one-way valve. The brake booster likewise lacks a one-way that it apparently should have.

So in essence, this not only explains why my HVAC has been acting odd but also highlights a series of major vacuum issues which are most likely the primary contributing factors to my engine continuing to run like an utter pile despite my giving it a total tune-up. I'll say again, the installer clearly had a good sense of how to install an engine so that it stays where it's put but as far as integrating it in a swap situation they had their head placed on the wrong end of their body! Lucky for the car, my other vehicle is a Swede with nearly a quarter-million miles on it. If I can keep that beast in running condition, I reckon I can clean up a poorly lumped Jag.

 

@millster

The good news is a few of us have original cars so we can help you work out what's not there on yours!

Let me know if you need any other info or pictures........

 

Reckoned it was time for a quick update. I'm making progress on the vacuum issues. I've replaced a few perished lines and things are working overall better. I just have to purchase the check valves and I think I'll have all of that mess cleared up. What I'm learning in the process is that whoever did the heart transplant on my beloved Jag did it with all of the finesse of a drunken surgeon. The cooling system is oversized, as it should be but they did not put a catch bottle in at all and the cap that is on the bodged system blows most of the coolant out as soon as the engine reaches temperature. I don't feel comfortable replacing the cap and letting the system come to pressure without replacing the hoses, so there is more time spent.

The part that annoyed me the most was realizing that I was "losing my cool" again. When I checked into why this might be the case, I found the high-side rubber line to be resting against the petcock for the radiator drain... with a decent rub-through on it. Not enough to lose oil in the refrigerant system but surely enough to degas. Once I get my Saab rebuilt, it looks like I'll be tearing into the Jag.

 

The last update for this thread:
I fixed my vacuum issue. My local Autozone only had one vacuum check valve in stock at the time I went. I was able to place it in line with a tee so that it not only serves the cabin ventilation system but also the brake booster. The bad news is that the seals in my brake booster took the damage of an unchecked vacuum system already.
The good news is that my A/C blows cold and consistent regardless of throttle position and that's vital.

As for the other issues I mentioned, let's just say I'll have a few more threads starting over the next few days.

 

@Millster

Glad you are making progress :-)

 

Hi Sarc,

i too have recently purchase[IMG][/IMG]d the vacuum lines for my 84 SIII, i have included some pics of where i am currently at , i am curious to know which size hose you used for one coming out of the t section into the back of the inlet manifold at the rear on my photo its those that passes behind the number 6 injector,

i used hose "b" as it was too tight for hose "A" but will now need to clamp down at the t section as the hose it too loose

https://www.jaguarforums.com/forum/m...etty-20200.jpg