AED air supply pipe

[Tintin]

On the S1 engines there is an insulated pipe supplying the AED with hot air from a pick up unit at the back of the exhaust manifold on the opposite side of the engine. On mine the pipe is fine but the insulation has crumbled to dust. Apparently the insulation is important to keep air temperature up for correct AED operation The pipe/insulation is NLA from SNGB and DMG.

Has anyone else replaced the insulation and what did they use?

Thanks.

Robbie

[oldtimer]

Hi Robbie,
I've just been reading about A. E.D.'s in my XJ6 SERVICE MANUAL. Cor Bennett, what a complex devise. Do you have access to the Description and Operation of this unit ? You really do need to have a read to understand what it's all about. Yes , I can now understand the significance of the pipe insulation to which you refer but truly that is only part of the story.

I now have a slightly better idea of the AED problem you experienced on departure from Gaydon on that freezing cold day.

As for insulation material, asbestos tape or string was liberally used but there is probably an almost as good asbestos free material available used on exhaust pipes. Alternatively there is a company at Abingdon that ceramic sprays pipe work. I have their brochure somewhere. One day I want to ceramic spray the exhaust down pipe on my V12 to protect the power steering tower, the heat cooks the top seal which then leaks - probably the same on V12 XJ- S 's

Talk to you soon

[Tintin]

Thanks OT.

The AED pipe OD is 16mm and I was thinking of using pre-formed foam pipe insulation from standard 15mm copper tube, but I need to find out if the material comes in an appropriate wall thickness (about 6mm only - for clearance etc) and if it will withstand engine temperatures and fluids. My AED has been modified (bi metal replaced with manual cam system) so temperature is not that critical, but I would like to keep it as designed if possible.

I am just about getting my head around AED operation (from the manual you refer to). I had thought that the stalling under load from cold was non operation of AED enrichment under manifold depression but I am now thinking that it is an air supply issue; hence removal of the pipe to check for blockages. Also I see recent posts (Clive Rothwell I think) re stalling relating to ignition timing adjustment. I set mine at 8 degrees BTDC as per the manual but will try adjusting as per the posts suggestion to advance until the engine pinks and then back off slightly (which may give more than 8 degrees).

Robbie

[oldtimer]

Robbie,
I only wizzed through the Manual references so still not fully conversant.
So, you say that the bi-metal functions have been removed in favour of cams ( is that hear say or have you checked) if that is the case, then the air supply pipe insulation is an irrelevance as the gas flow temperature had a direct bearing on the function of the bi-metal strips (as I understand it) You say that air temperature is NOT SO important - if the bi-metal strips have been removed what part does temperature play, if any ?

As for retaining original design features, surely a working enrichment devise takes precedence. I have never owned a vehicle with this type of AED but down the years have read of many complaints. Did they ever work to spec ! My earlier vehicles had an electric choke of an earlier design. You could guarantee that the engine started regardless of ambient temperature but leave it running un attended at your peril. As a result must people fitted a remote switch to shut it down. Left running it would over fuel and choke it's self to death .

Where exactly does the air supply come from ? Is there a tapping from that rear manifold, if so I would be checking to ensure that there is a gas flow at that connection as well as the length of the supply pipe. Have you had the AED off the vehicle to examine and understand how it works ?

With the engine up to a normal running temperature does it appear to perform satisfactorily at all engine speeds and regardless of gear selected ? If Yes OK then I would dismiss the ignition setting for the moment.

You appear to be chasing one or two problems at the moment, like the overheat problem - any development in that department ?

Regards

[Tintin]

OT

The manual choke conversion comprises cams operated by a traditional pull knob via a cable which open/close a) the fuel metering needle valve and b) the air inlet valve of the AED. The cam positions are adjustable on the shaft, allowing variations of mixture and idle speed.

I have rebuilt the AED on the bench using a genuine SU overhaul kit; thus I am fully appraised of its operation and all servicable parts have been replaced.

I agree that the insulation is not essential and if I can't replace it I will omit it. The benefit is warm air on cold starting thus improving combustion, running and warm up. I have also checked the warm air pick up/filter at the manifold end of the pipe and no obstruction.

The engine starts and idles easily from cold, it starts, idles, runs, accelerates etc well when warm - no complaints there at all. The sole problem is stalling on load from cold, but I have not run the car under load from cold since my last AED adjustments (pick up pipe awaiting insulation or a decision to re-fit without).

I fitted a cut out switch on the electric solenoid AED on my Mk II, so recognise the issues you describe there.

Replacement viscous fan drive and temperature sensor fitted - gauge now reading sensibly, fan drive much better; I have yet to take the car out on a run to test it properly, but to date no overheating. I drilled the old viscous coupling to look inside - it was empty - all fluid had leaked out, hence no resistance to rotation, and cooling effect much reduced. Coolant changed - old coolant clear blue - no evidence of rust or sludge at all (pleasantly surprised). Yes, I did drain the block as well! Radiator and thermostat replaced by previous owner; all old hoses replaced during coolant change.

New (bi metal operated) AED units are available (at a cost) from Burlen Fuel Systems - but I am determined to try and get my old one set up correctly before I ask Santa for a replacement!

R

[Tintin]

Have ordered Armacell foam pipe insulation 15mm x 6mm wall thickness based on manufacturers claims of +110 degrees C suitability, oil resistant, Class O fire rating. Less than £2 +P+P for 2 metres. Downside = 1 week delivery. Will let you know if it fits and functions!

Robbie

[oldtimer]

Hi Rob,
An interesting and logical summary of actions taken - well done.

The next road test should prove interesting, I await the result !

P

[stevewarbs]

Hi Robbie

I think the problem may be more to do with your transmission than the AED.

I have removed the AED completely and whilst the car is now difficult to start, once she is started I let her idle for a minute then put her into drive and leave her a few seconds. By applying gentle pressure to the accelerator she will pull off and once moving full power can be applied almost immediately but too much accelerator to start and she will stall.

I don't understand the workings of an auto trans but I believe it is to do with fluid draining from the torque converter overnight.

[mike020150]

Auto transmissions do drain oil back into the sump when left to stand just like engines. Again just like engines, after a cold start, transmissions take a few seconds to pump the transmission fluid through to the torque converter and throughout the valve body eliminating air locks which can cause initial jerky progress. However, that pressurising doesn't take much longer than it takes to circulate the oil around a cold engine. The obvious exception is when there is a fault in the valve body, a dirty transmission oil filter or if an O ring or similar around the oil pick up pipe has failed. Transmission 'sucking' noises which carry on beyond about 30 seconds after a cold start can be a clue to such problems. Mike.

[CliveRothwell]

Hi
I admire your determination with the AED. I felt the same way for a long time and having rebuilt a spare set of carbs and put together a good AED with manual choke cable modification, I eventually gave up and bout a new pair of HIF44s with manual choke built in. That cured the starting issues immediately but it was expensive at a time when Burlen were still trying to solve the AED spares problems. I wanted to drive the car not tinker with it as much as what I was doing hence the eventual decision to go for new carbs. It also looks "more standard" than the AED conversion.

As an aside, the car is marginally better as a I discovered last week that most of the carburettor flange nuts were not all that tight and indeed, one was not done up! I did not fit them originally - an expert did. I must say though, I hadn't checked them until the other day.

Keep up the good work!