OK Ben

Cheers, I'll have another look at it in daylight, and see what I can come up with

Thanks for your help

Alex

 

For what it is worth when mine was hunting it never really got much past 1400 - typically it would bounce between amost dead and high rpm, it took a fair bit of cranking to provoke ignition - my AAV worked but it never truly closed off and was slow as molasses in a freezer.

 

Hi Ben

Cheers!

I had a Hunting problem too after the Winter but after running for a while it eventually put itself right

Which always seems to happen after a bit of a lay up but now I just take that as normal as it always eventually clears

 

OB
The hunting (ie too high idle being cut at 1400 rpm by the ECU) is because the AAV is sticking, and after a bit of use it unsticks itself.
Take the B bank air cleaner off, and you will see the outlet on the RHS of the back plate of the aircleaner that gives the air feed to the AAV bottom air inlet. Assuming the car is cold, just block this off with something solid (eg a wood plug wrapped round with a big cloth, with the ends of the cloth NOT in the hole, so the plug and cloth cannot be sucked into the AAV) and start the car. If you are worried about the dizzy oiling, pull off the top vent outlet from the dizzy cap.
See what happens when you start the car and report back. If the car will not run without throttle from you, then the AV is the problem. If it will, you have an air leak somewhere, or throttle butterflies unadjusted etc etc.

 

Hi Greg

Cheers!

That sounds like a Plan!

First a Couple of Questions if you would be so kind

(1) If I pulled off the Top Vent Outlet Pipe from the Dizzy, what would happen? and could I leave it off permanently or is this just for the purpose of experimentation?

(2) What would happen if something got sucked into the AAV would it Wreck the Engine or just the AAV ?

(3) Is there a way to disable the AAV without unbolting it from the Engine and then just using Throttle from myself ? as I am Paranoid in case a Bolt Snaps off or Strips the Thread

(4) At what Temperature does the AAV Piston Start to Close, as the only problem is on Initial Start Up when the Engine is Stone Cold, as on Initial Start Up the Engine Roars away at about 1700-1800 RPM which always tends to freak me out up until the OIL Pressure Starts to build up and that is the reason why I have been putting her into gear as soon as possible, where it goes into gear with a 'Clonk'

With neither of those Two options being an ideal Scenario but after the Stone Cold Start up then She will Stop and Start Perfect all day long at Sensible Revs being 1100 and then quickly dropping down to 750 RPM Hot Idle

Since I always have the Bonnet/Hood open to do all the Pre-Flight Checks before moving off, the GF came up with a 'maybe' Not so Crazy idea that might just work! and this involves playing a Hair Dryer on the Body of the AAV to get the Piston Closing before doing a Stone Cold Start Up

And if I knew at what Temperature the AAV Piston Starts Closing then I could Check this with my Heat Gun Thermometer and then in future I would know how many Seconds of Hair Dryer Heat I should give it

While this may sound like a lot of messing about, She may have just come up with the Perfect Solution!

What say you?

 

Hi Greg

Cheers!

That sounds like a Plan!

First a Couple of Questions if you would be so kind

(1) If I pulled off the Top Vent Outlet Pipe from the Dizzy, what would happen? and could I leave it off permanently or is this just for the purpose of experimentation? Nothing

(2) What would happen if something got sucked into the AAV would it Wreck the Engine or just the AAV ? It might bung up the AAV but it is not at all difficult to bung up the airbox feed. Think of a bit of dowel almost the same diameter shoved into the middle of a decent sized tea towel and shoved into the hole with the tea towel mainly outside the hole.

(3) Is there a way to disable the AAV without unbolting it from the Engine and then just using Throttle from myself ? as I am Paranoid in case a Bolt Snaps off or Strips the Thread Do what i suggest in 2 above!, the only way to disable the AAV is to block its air feed.

(4) At what Temperature does the AAV Piston Start to Close, (No idea, but the coolant cannot start to warm for at least 30 seconds) as the only problem is on Initial Start Up when the Engine is Stone Cold, as on Initial Start Up the Engine Roars away at about 1700-1800 RPM which always tends to freak me out up until the OIL Pressure Starts to build up and that is the reason why I have been putting her into gear as soon as possible, where it goes into gear with a 'Clonk' Do as suggested in 2 and try a start, the engine will almost 100% certainly not roar this time, the test only has to be for a few seconds to prove the AAV is the problem. Only after that do your your courage boots have to be donned to removed and fix the AAV! but see the next reply...

With neither of those Two options being an ideal Scenario but after the Stone Cold Start up then She will Stop and Start Perfect all day long at Sensible Revs being 1100 and then quickly dropping down to 750 RPM Hot Idle This seems to indicate the AAV might be OK, or that only when it is STONE cold is something going wrong. However, these results are also consistent with a sticking throttle butterfly after a night's inactivity. In your position I would first check carefully and clean the throttle bodies anyway, and also check the throttle return springs, butterfly bearings, capstan and the bearings the throttle mechanism runs in are all lubricated and turn easily, and that the throttle rods have a mm or two of slack at the closed position.

Since I always have the Bonnet/Hood open to do all the Pre-Flight Checks before moving off, the GF came up with a 'maybe' Not so Crazy idea that might just work! and this involves playing a Hair Dryer on the Body of the AAV to get the Piston Closing before doing a Stone Cold Start Up

And if I knew at what Temperature the AAV Piston Starts Closing then I could Check this with my Heat Gun Thermometer and then in future I would know how many Seconds of Hair Dryer Heat I should give it

While this may sound like a lot of messing about, She may have just come up with the Perfect Solution! I hesitate to disagree with the GF, but i think that having done all the above checks, and assuming nothing was found, a 10 second start with the AAV blocked off would be a more reliable test!

 

I would also add that having a good idle when warm is no indicator - you may find that you need to wind the hot idle adjust outwards - it may be turned in to compensate for an air leak but I don't know if you have touched it or how many turns out it is. Although ambient temperatures my cause a different result the theory here is that the car won't start and stay started without your input from cold - if it does then it is likely that air is getting in where is shouldn't. A very high idle speed cold is a good indicator of air leaks. I don't know how much fettling and adjusting you have done - I know you have been busy - setting the idle correctly starts with the throttle butterflys and working back out.

I put the service book stuff below- not sure I understand how total closure won't affect idle speed which they state should be 750rpm, which is why I suggested taking the AAV out by restricting its air. There is no data in the Jaguar docs I have that lists temperatures for the AAV.

AUXILIARY AIR VALVE
Test 19.20.17
1 Remove left-hand air cleaner element, see 19.10.01.
2 FuIly close idle speed adjustment screw.
3 With engine at normal running temperature, blocking auxiliary air valve inlet should NOT affect idling speed. If idle speed affected, continue with operations 5 to 1 I. If idle speed is not affected continue with operation 4.
4 Reset idle speed, replace air cleaner element.
5 Remove auxiliary air valve, see 19.20.16
6 Fully close idle speed adjustment screw.
Immerse auxiliary air valve bulb in a container of boiling water and observe valve head through side port. Valve should move smoothly to closed. Quickly blow through side port; no air should pass.
Allow valve bulb to cool. Valve head should move smoothly back to open main air passage.
10 If valve performance is satisfactory reset idle speed adjustment screw and refit valve.
11 If valve performance is not satisfactory, fit replacement component.

I don't know if there is a temperature curve published anywhere - somebody that may know the answer is the chap that refurbed my AAV - I'll ping him and see if he has such a thing.

 

I do not fully grasp the logic of this official Jaguar manual point highlighted in 3 above. As far as I understand it, if the AAV entry is blocked, the slow running air feed is also blocked.

 

Agreed - that is also my understanding - I think that test is flawed

 

Hi Greg and Ben

Thank you both for your detailed replies

'Greg' if I Block the Air to the AAV inside the 'B' Bank Air Cleaner with a Dowel, is there any Danger of Oil Being Sucked into the Dizzy as had been mentioned by Doug, as that could be a Nightmare sort of problem to sort out

'Ben' The Hot Idle Screw has never been touched during the life of the Car as far as I know and Certainly not by myself

One thing that I may have either glossed over or else failed to mention was:

On a Stone Cold Start Up, the Engine will roar away at 1700 RPM up until the Oil Pressure has started to Build (30 Seconds) where once having done so, She then settles down to idle at a more sensible 1100 RPM and then by the time that I've got her out of the Garage, the idle is almost down to the Hot Idle Speed of 750 RPM

The thing that really scares me is the thought of the Engine revving away for 30 Seconds, before the Oil has got round, which maybe wouldn't happen on Cars that are used every day, except that ours is more used for 'Tripping' at Weekends

 

I got pretty extreme in my last AAV go around. And learned, as GF said, no two AAVs are the same.

I'd gotten my hands on a second unit which gave me the courage to experiment a little. So I opened the second one with the GF method, cleaned it sealed it and installed it. And yes, pushed the top hat down MORE than the old one, smaller opening. I also didn't like the revs at start. Tooo high, 1200, 1100, 1300. Tooooo high.

In my working on the second AAV before install I was very surprised at the strength of the spring and the pressure the wax bulb produced pushing on the TOP HAT.... In my last go around (a million years ago it seems) I'd only used JB Weld epoxy to secure the TOP HAT on reassembly. This time (due to a better understanding of the forces involved in the spring, bulb and sliding piston), I also drilled a very small hole and used a very small self tapping screw to add some added hold to the position of the top hat. This worked out to be a good thing later with experimenting with the final position of the top hat. The reason for the screw was to help with my fear, with my active imagination, pictured the JB Weld failing somewhere in a small mountain road in southern Vermont, the top hat POPPING off running the RPMS up to uncontrollable,,, so the set screw gave some added reassurance... Anyways

So, the "new" AAV installed and started her up. RPMs soared to something like 1800 (as Alex is experiencing). I was shocked and pissed, I must say. Removed it and back to the Lab.

Scraped off a bunch of JB Weld. Then, started using the set screw (using the set screw hole on the CASING of the AAV but ignoring the initial set hole on the TOP HAT side) to find the "right" height for this particular AAV. I would thread the screw out some with a stubby and/or L shaped driver, then back, allowing me to test for an UP and DOWN range for a right TOP HAT height. Eventually (not long) I found it. Around 900-950 rpms at start, cold. THEN I gooped it up with the JB Weld. I'm sorry I don't have pictures.

In this AAV, the opening is VERY small when cold. The AAV is from a Hess car, but all the numbers on it match the original.

The car doesn't start as quickly as it used to when cold. But, somewhere in all the reading here, I remembered GF talking about turning the ignition key to ON/RUN, and fully pumping the pedal 2 or 3 times to prime a bit of fuel in each cylinder before start,,, then turning the key when the beast is cold. This worked and the car starts faster this way than it used to. All good. I finally have a fine tuned type of control of my idle - which then allowed me to better set everything to do with the throttle, buttery, arms, links ect. A good good thing.

​​​​I am a bit worried about starting when winter hits here. I also don't want to put a lot of strain on my starter with 10 or 15 second key turns at start, but I'm in a good place for Spring, Summer and Fall. We'll see.

 

Indeed they are different, I reached out to Jonas who refurbed mine and he sent me the image below that shows openings for given temperatures - indeed they are not all alike. I have sent Jonas the link so perhaps he will join in the thread.

 

That would concern me also - my XF does it by design and I'm not happy about it, I don't think anything good can come of such high rpm immediately on start. I'd be OK cranking a while to get oil moving - better a starter than an engine replacement

 

Hi Greg and Ben

Thank you both for your detailed replies

'Greg' if I Block the Air to the AAV inside the 'B' Bank Air Cleaner with a Dowel, is there any Danger of Oil Being Sucked into the Dizzy as had been mentioned by Doug, as that could be a Nightmare sort of problem to sort out Not if you remove the tube from the dizzy top

'Ben' The Hot Idle Screw has never been touched during the life of the Car as far as I know and Certainly not by myself

One thing that I may have either glossed over or else failed to mention was:

On a Stone Cold Start Up, the Engine will roar away at 1700 RPM up until the Oil Pressure has started to Build (30 Seconds) where once having done so, She then settles down to idle at a more sensible 1100 RPM and then by the time that I've got her out of the Garage, the idle is almost down to the Hot Idle Speed of 750 RPM Alex it should take 6 seconds AT MOST for the oil pressure to come up after the engine fires. Is it rally taking 30 seconds? If so, what oil weight are you using, is the filter OK?

The thing that really scares me is the thought of the Engine revving away for 30 Seconds, before the Oil has got round, which maybe wouldn't happen on Cars that are used every day, except that ours is more used for 'Tripping' at Weekends It would scare me too

 

The idea is to build oil pressure as fast as possible. Cranking revs don't do this, it actually causes more wear than a fast start. The engine right after starting also has no load, so it's not as bad on the internal components as you might think. Also the modern engines use light oil, like 0W-20 and that flows quite quickly. I'd never use 20W-50 in a V12 for example, it's like sludge on startup.

The ideal is like large industrial engines that use a prelube system to build oil pressure before cranking, but that's not practical for a car engine.

 

The gauge is heavily damped too, I'd use when the low oil pressure light goes out as a guide, not the gauge.

 

The AAV piston in controlled by a wax capsule ( like a thermostat) which sits in the coolant. A hair dryer heating the body won't help, as the heat needs to come from the coolant to move the piston.

Like Greg mentioned, I think you have a sticking piston in the AAV. I have tried spraying lubricant down the bore with no success, the only way I was able to fix it was rebuild or replace the AAV. I'm not sure if rebuild kits are available anymore.

 

In a decent engine they should - with modern lubricants some of this hi RPM start stuff may be justified in an engine that is run regularly, the V12 however is not modern, some of these cars spend extended periods of non running so you can't always rely on an oil film get out of jail. Run an engine on tickover with no oil and it may run for a while - rev it hard with no oil and see what the additional pressures of high rpm cause. This is precisely why larger engines have priming circuits - were it the case that high RPM starts were viable large engines would follow the same principle. Beware the reliance on the 'idiot light' the pressures at which they trigger (circa 5 to 7 psi depending on manufacturer) it is usually all over by they time they're spotted. Guess I may be too old school but high RPM on startup is an alien concept to me, goes against the grain. I am time served - but a long long time ago - like late 70's ....

The guage is damped but not really by design, it is more the performance of electrical instruments of the period, I wouldn't argue either if anyone questioned its accuracy. The gauges in the XJS in general should be considered indications but not guaranteed confirmations - my oil pressure gauge takes forever to rise, rarely shows more than 50 but I've measured 60psi with a mechanical gauge.

I actually asked Ford why my Jaguar V8 did the high RPM thing - the response was 'it adds to the theatre' - there is no solution, well their may be but they declined to provide one.

 

Wow! I didn't know.
Thanks for this!

 

Hi Greg/Jagboi/Jay/Ben

Thank you all so much for your help and very detailed replies

So I'd better start off with with a couple of questions before I let you know what I did and what happened!!!

(1) At what RPM would you be happy to drop a V12 XJS into gear

(2) If I Blocked up the Pipe that goes through the back of the 'B' Bank Air Filter which as I understand it would disable the AAV could I leave that in place as a permanent Fix rather than take off the AAV unit itself

(3) Would it be Safer to pull the Rubber Pipe out of the back of the Air Box before I blocked the Pipe of, as if the dowel fell out and went into the Throttle Body then it would be Game Over

OK here is what I did and what happened, with a Surprising Result!

First of all in response to Jagboi's Question: I'm using 10/40 Semi Synthetic

The Next bit is from memory but I Video'd the whole thing and so the figures I'm giving you now may not be accurate and also the Oil Pressure almost certainly took less than 10 Seconds as hopefully the Video will Show when I get it put up Oil Light probably went out at 6 Seconds but I didn't get that on Video (Now Updated)

This is on a Stone Cold Engine: Ambient Temperature of the outside of the AAV was about 16c (I may return to edit that when I play the Video Back)

Next Again with the Engine Stone Cold and Un-started I warmed up the Outside of the AAV to about 25c with a Hairdryer as confirmed by my Laser Gun Temperature Gauge although it still felt Cold to the Touch

Then I took the Brave Pills and Turned the Key!

As expected She Started on the Button, only this time the Engine did not run away to 1700 RPM as She sometimes had done before (Ambient Temperature does seem to make a big difference)

But this time as soon as She Started the RPM was around 1200 - 1400 RPM and about 6 Minutes and 30 Seconds later, the RPM was just on 1000 RPM (Updated)

Again I will check these figures with the Video and come back and edit to get it more accurate

As for how long it took for the Oil Pressure to build up, I have to admit I was so fixated watching the RPM that 30 Seconds may have been a bit of a Wild Guesstimate but the Video Should tell all

If I had kept the Hairdryer on longer and got the AAV to 30c then I think the Tickover would have been right there at about 850-900 RPM and then going down from there

Jay that's an Amazing Fix, so well done on that!

Figures Now Updated on this Post