'86 XJ6 VDP extremely rough running and cutting out

Yes it sounds like it could be AAV or coolant temperature sender as culprits. The arrow in your photo points to the AAV. Another possibility would be there is nothing wrong with the AAV but rather the hose behind the AAV which you will see only after you remove the AAV which leads to the intake manifold. Since I cannot crawl under the car and am not willing to raise the car even with jack stands, I visited my honest mechanic.Before doing so I purchased the two AAV hoses from SNG and brought them with me to the mechanic. I had the car towed there.While I was at it I also ordered from SNG the ‘accordian shaped’ hose which runs from the air flow meter to the throttle body and asked the mechanic while installing it to clean out the throttle body as well. That was a year and a half ago. Last week the car was due for its semiannual smog test. It passed with the best numbers I’ve seen in the 24 years I’ve owned this 1987 series 3 XJ6.

Hello Alan, that does sound similar to my issue. From the picture, yes that is the AAV, that is where you detach to see the valve, but that doesn’t look like a kink to me, mine had been much worse.
The hose itself goes to an idle control air block (not sure the technical term for it), but it’s the shiny square metal thing to the right of the throttle body in the picture, with the red circle over part of it.


I did find it quite helpful to have a flashlight/camera device, as looking through where the hose detached was quite dark. I haven’t verified my new fuel pump and filter to have solved my issue yet, I’ll see for sure when I get home in a few days and finish installing everything.

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The AAV (square base) is clamped to the water jacket by 4 bolts/hex and a ‘tower’. It as an electric connector and a hose - which comes from the 'air distribution block shown in Grahams picture…

The simple check is to disconnect the hose and peer inside. The slide seen should be around half open with engine cold - and closed with engine/AAV hot.

It’s important, if no faults are found to inspeck the hose underneath the AAV - if disconnected the engine will likely stall as fuel is leaned out with increasing engine temp.

In addition to your checkpoints; verify that the fuel pump is running with ign ‘on’ and the engine running. If not; the engine will stall as the fuel rail is emptied by the engine consumption. You will also then notice that fuel return stops…

Frank
xj6 85 Sov Europe (UK/NZ)

Frank and Graham…excellent photo and clear explanations. As a gynecologist I spent my career working in “dark places”. The anatomy and physiology of an engine is, in a sense, largely what this forum is about. With that said, I’ll begin my dissection knowing there will be many questions along the way…many thanks.
Alan

Alan,
Thanks. That photo is one that I took of my 1984 XJ6 Vanden Plas that I posted in the 2020 time frame in a string about vacuum leaks and how to adjust engine idle using a 7/32" hex tool in the air distribution block. Here is the link to that string if you are interested in reading more.

Paul

I have no idea what I’m seeing…

This looks like a great deal of debris and no clear evidence of a “flipper” valve?! I suspect you will suggest AAV removal but I can only see 2 bolts attaching to water (hatch).


Am I headed toward a new AAV?

Simple things first, fuel pressure, temperature sender.
I see the sooty, scratchy AAV slider, you have to tell if that moves but I don’t think it’s your problem. Simple test, with a bit of throttle, does it stay running? That’s all the AAV can do.

Alan,
Do you own copies of the Series III XJ6 Service Manual and Parts Catalogues? If not, this would be a good time to get them to help you understand more about your car, the parts in it, and routine service and repair tasks.


I got my hard copies on eBay about 22 years ago and I still use them regularly.

Paul

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Took your advice, Paul…both are on their way from eBay…both used paperback.

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Thanks David
Should have said that the engine was stone cold. It looks like valve is stuck open and a lot of debris. Doesn’t look like any of the images I’ve seen on this forum…??

Might be okay, but now that you’re there you can give it some brake cleaner or similar, and exercise it carefully with a screwdriver to make sure it moves freely. It’s just a bimetal spring that closes the valve as it getes warmer… and it just increases air exactly like the throttle would.

It’s looks equally unfamiliar to me, Alan…:slight_smile:

Early versions did not have an electric connector - but still had the slide and the air hose from the air distribution block. And that hose seems to be missing on yours (seems more like dilapidated wires at the hose’s place?).

Adding that while the late versions were bolted to the water jacket two screws on the base plus the two screws at right angles to the base. On your picture marked with green arrows and ‘round’ - which likely means internal ‘hex’ or ‘star’ bolts. Also, on early versions, the base was open to the coolant, so draining coolant was necessary before AAV removal. On later versions the base clamped (4 screws) to a polished part of the water jacket - and draining was unnecessary…

So your bewilderment is entirely justified; the early types were only used briefly - and is seldom encountered…:slight_smile:

In my opinion; your AAV does not appear to comply with what I see as normal for the early types. Unfortunately; the early and later AAVs are not interchangeable - but the parts catalogue you have ordered may clarify matters…

In the meantime, David’s advice is sound; the AAV just increases air flow and a light throttle should keep the engine running - if the AAV is the problem…

Frank
xj6 85 Sov Europe (UK/NZ)

Can I determine early/late version by VIN:

SAJAV1341GC431855

Alan,
Attached are some pictures of a EAC3883 Extra Air Valve (EAV) that I removed from one of my Series III XJ6 parts cars and subsequently sold on eBay.




The pictures show the EAV with the slider closed and open, and also from two sides. Perhaps these pictures will help.
Unfortunately Jaguar also called this device the Auxiliary Air Valve (AAV) so some folks use EAV and AAV interchangeably.
From your pictures I can clearly see that your EAV is open but a bit dirty. The fact that there are two different types of fasteners holding the EAV to the coolant rail tells me that someone had removed it before, lost the original fastener, and so they grabbed whatever else they had that was handy.
The final picture shows the EAV circled in red in my former 1984 XJ6 Vanden Plas after I removed and replaced the original failed engine with one from one of my parts cars and then cleaned up the engine bay.


BTW, if your hoses are original then they are hardened with age and well past their useful lifetime. The hose that you can easily see from the right side of the engine and goes to the Air Distribution Block is EAC1596 and the hose beneath that connects to the intake manifold is EAC1471. The usual USA based parts suppliers like Moss Motors, SNG Barratt and Welsh Enterprises will likely have them available.

Paul

Update: AAV entailed removal of 2 star head bolts.

The slot valve appeared normally open (cold).

I did boiling water test (per my new Service Manual) and valve closed all but about 1-2mm of ‘slot’ showing. (No pic)
I plan to get new hoses and replace CTS’
Questions

  1. Would a lubricant or cleaner be safe to help full closure or is 1-2mm gap OK?
  2. Is there a gasket on base plate,I didn’t see one.

Thanks for part #s Paul…and everything…Alan

Forgot…resistance across terminals= 20.6 ohms

I see absolutely nothing unusual with the AAV, Frank.

  1. yes, but I wouldn’t, and the gap doesn’t really matter.
  2. no

Resistance will be fine, put it back in and good luck solving the actual problem :slightly_smiling_face:
You don’t need new AAV hoses. Spend that money on a decent pressure gauge to check the fuel pressure. I think that is where you’ll find the problem, unless it’s the CTS.
If it is very cold where you live, unplug the cold start injector and see if it changes anything, just to rule that out.

With the AAV out, David - neither do I…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

[quote=“Alan_Munson, post:75, topic:436930, full:true”]

I did boiling water test (per my new Service Manual) and valve closed all but about 1-2mm of ‘slot’ showing. (No pic)
I plan to get new hoses and replace CTS’
Questions

  1. Would a lubricant or cleaner be safe to help full closure or is 1-2mm gap OK?
  2. Is there a gasket on base plate,I didn’t see one.

I assume the service manual did not advice submerging the AAV in water, Alan - there is electricity involved…

If only the notch is visible when hot, it is as should be. A small screwdriver in the notch can be used to exercise the slide - and some solvent to clean and clear the sliding is appropriate - oiling is not, it collects dirt.

The slide is moved by a bi-metallic spring, heated either by the engine heat or by an electric heater coil. The intention of the latter is a quicker closing of the slide when the engine is running. Either 20 or 36 ohms, depending on version, is correct. Otherwise, engine temp regulates the slide to the appropriate opening for restart…

Unless the mounting is open to coolant, a gasket is not required - clean metal to metal contact transfers engine heat to the AAV…

When refitting; ensure both hoses are properly attached…

Frank
xj6 85 Sov Europe (UK/NZ)