AAV Manifold Bleed Pipe

XJ
1

I have a 76 XJC that I recently acquired and I noticed on the AAV a fuel hose coming off it and not going anywhere. I looked in the Haynes book and it supposedly goes to a “manifold bleed pipe” that is not in the car. Can someone please explain what the bleed pipe is for and where it should route to. I can’t find any information on it other than info about the AAV itself.

Thanks,
Darrin

2

I should have mentioned that it’s a V12

3

Darrin no assistance with the bleed pipe but you can edit your post if you see there is a mistake or wish to add to it, there is a pen icon lower right on the initial post.

4

It goes to the distributor and it’s for venting.
There must be another hose from the distributor attached to a fitter.

5

The AAV of the V12 is combined with the idle screw, Darrin - there is no fuel or fuel hose involved, only air flow…

Ref Aristides; hose will indeed ‘suck’ air, and if the length fits and there is a nipple fitted for it at the dist - you’re on. Don’t confuse it with the vacuum hose for vacuum advance…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

6

Thanks for the info and what you say makes perfect sense. However, the only port on my distributor is on the vacuum advance capsule. I don’t see another port for vacuum.

On other cars I’ve seen online it looks like the hose I’m talking about goes into a hard line next to the intake but I don’t know where that hard line would go and why it’s missing.

The former owner had about 3” of fuel line coming off the back of the pipe that goes on top of the AAV and it doesn’t look like the line was cut but looks like it went into the so called manifold bleed pipe that’s no longer there.

Would anyone have any pictures of how I would route this vacuum line and where I connect it?

7

There must be a spigot on the top of the distributor cap, see if it’s broken or caped.

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8

The primary purpose is to take filtered air though the AAV to the inlet manifolds, Darrin. The flow is regulated by engine temp (AAV closing as engine temp rises) and the idle screw. A PO may have removed parts, leaving hose stub with nowhere to go. I have limited experience with the V12 and cannot tell ‘what’ in this case - or what the PO intended…

While musing; just plug the hose - it’s irrelevant for engine running…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

9

Thank your Aristides. I do have that spigot on my distributor. That helps!

10

Thank you Frank! I’m assuming it would be better to cap it off vs going to the spigot on the distributor?

I’m all for eliminating and simplifying if it doesn’t improve how the car runs.

Thanks
Darrin

11

Jaguar put the effort, and money, to install the distributor venting system for a reason: To keep the cap cool and to prevent it from blowing up if by any chance excessive fumes accumulate inside a device the generates twelve sparks on every rotation.
A very simple and effective solution not worth simplifying.

1 Like
12

I agree with Aristides, Darrin…

Though I haven’t really heard of distributors blowing up or burning without ventilation - when the easy precaution is just a matter of attaching a vacuum hose; there is no valid reason to ‘simplify’…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

13

Understandable. I appreciate the help from both you and Frank here. There was not much information on this and has been a huge help. I will certainly follow your advice and thank you both very much.

Darrin

1 Like
14

This illustration shows the distributor vent system

https://parts.jaguarlandroverclassic.com/parts/index/part/id/898.1469.4857.21678/brand/jaguar/

And this shows the elbow hose to the AAV with the nipple for the distributor vent hose

https://parts.jaguarlandroverclassic.com/parts/index/part/id/898.1469.4856.21676/brand/jaguar/

However…

Your 1976 car would have the pre-HE V12. I am not aware of the distributor vent system being used on the pre-HE engines and I don’t see it in Series II catalogs. And the AAV valve and plumbing is quite a bit different on the Series II/Pre-HE cars.

I was hesitant to mention this because I didn’t want to confuse the issue and, what’s more, I know so little about the Series II cars.

On the other hand, if your engine has been swapped, or the original engine has some parts from a later model engine, it would probably be a good thing to know about.

Cheers
DD

15

Hi Doug,

It would appear that somewhere down the line the engine was swapped out with a later HE engine. However, the opus ignition and djetronic injection system were kept.

So I guess I’m more confused now on how I should proceed. :grinning:

Thanks
Darrin

16

Well mix-n-match parts can be a source of confusion, yes. It sounds like you have an Opus distributor with an HE/CEI distributor cap? I’m not sure if that presents any concern in and of itself. But, if everything is there for the distributor vent system then I’d certainly make it functional. I can’t see any reason to avoid doing so.

Let’s hear what others have to say. Again, my knowledge of earlier engines/systems is thin. I don’t want to complicate things needlessly

Cheers
DD

1 Like
17

Cannot see that the dist lid should vary with model year, David - permitting a PO some leeway.
Generally I would assume that pre-HE and HE differences related to the engine itself, the vacuum advance set-up and possibly the ECU?

Frank
xj6 85 Sov Europe (UK/NZ)

18

I think the HE and Pre-HE caps would physically interchange and work OK…if the matching rotor was used. Don’t take that to the bank. :slight_smile:

Significant differences in ignition and fuel injection, yes. And of course different cylinder heads and pistons. And what other details…?

Plus, between the regular Pre-HE and the HE there was the short lived (and very desirable) hot rod pre-HE variant built for less than a year…which had it’s own features.

Cheers
DD