Engine running problem

[pvsingleton332]

Hello
I have a i965 Mk2 3.8 . I tend not to use it during the winter months but regularly go to start it up.
On a number of occasions this winter i have started it with not to much trouble. i run it for a good 20-30 minutes gradually building up the revs to 2000-2500 so as to simulate a good run. Engine temp around 55-60,oil pressure 45-50,all good. Then ease off revs slowly. Just before reaching idle at around 1000 revs it just dies on me. Try to restart and nothing, turns over strong but no firing, not even a kick. I leave it, come back another day when cold it fires up no problem, then same routine again. Did have a couple of backfires when applying a couple of high revs, but otherwise ran smooth.
Any suggestions please, it has been suggested the coil, but other than a couple of backfires runs smooth.
Thanks Paul

[Andy P]

Hi Paul and welcome to the JEC Forums.
Although I do not have a Mk2 Jaguar your problem takes me back a good few years when one had to eliminate components to find the culprit.
Just my thoughts on the coil,when the no start happens again see if there is a spark at the plugs and what sort of spark(weak or strong).
It could also be that there is too much heat in the engine bay due to the car not going forward and affecting the fuel.
Just my thoughts,I'm sure someone more knowledgeable will have some other ideas.
Post some photo's if you can,would love to see your car.
Enjoy the good weather and hope you get to the bottom of the problem.
Take care.
Andy

[Dave_W]

Hi Paul,
Have you checked that the choke is turning off ? The choke staying on will cause those problems.
Regards Dave.

[piman]

Hello Paul,

difficult to diagnose.

The fact that it restarts later seems to indicate there is not much wrong? Personally I am not a supporter of running a car with no real load. Your coolant temperature will reach normal temperatures but the engine will not have got to the temperature achieved during normal running.
I.e, coolant temperature is not a true indication of engine temperature, if you had an oil temperature gauge it will show cold.

That said I don't know why it does what it does? The starting carburettor should have switched off if the water temperatuire reaches normal running level. It is quite obvious if it is not swiching off as the characteristic hiss is evident.

You mention only running the engine to up to 2,500 rpm, I don't know why you would restrict really opening the throttle? However running at idle does never equate to road running. Possibly the engine is being choked by your practice of starting it and running at no load?

Alec

[BookerME]

I’m inclined to agree. Occasionally I have a very similar problem with my 420. I’ve never managed to get to the bottom of it but strongly suspect it’s to do with running temperate and fuel, possibly flooding as the smell of petrol is the giveaway.
You can test the electrics when the problem occurs.
I’ve got my choke wired into a manual switch on the dash so can rule that out.
If you can, try taking it for a proper run instead of letting it sit there, that always sorts mine out.

Mac.

[pvsingleton332]

Sorry for delay in getting back. Thank you all for your comments.
The problem still exists.
I have checked for a spark after it cuts out, there is one though do not know whether it is strong or weak, think it looks OK.
Think that may rule out coil.
When it is running I do not get any interference on the radio, does this rule out condenser ?
This time after it cut out, so hot engine, I immediately tried starting. After some difficulty it started and ran smoothly. I switched it off from ignition, then immediately tried starting. Very difficult to start, with strong turning over but will eventually start. Same every time for a number of times. If leave engine to go cold it will start easily and healthily.
Little reluctant to take away from garage in case dies on me away from home, and cannot get started.
Carb float chambers a little damp but probably from repeated starting.
Its a mystery to me.
Any further ideas anyone.
Thank you for your help.

[piman]

Hello Paul,
I think that you should check the mixture, it may well be too weak? have alook at the plug colour and also the exhaust tail pipe colour, although that can be misleading as unless you do quite a few miles it may well still be black from several starts.
If the condenser was faulty your spark would be poor or non existent. Generally a car won't run with a faulty condenser.

Alec

[pvsingleton332]

Thank you for your comments Alec
The automatic choke is working, it switches off after about 3-4 mins from cold start.
If the mixture was weak, would it not be difficult to start when cold.
The plugs are on the black side, so might indicate to rich.
I've got a carb man coming over tomorrow, so hopefully he will get to the bottom of it.
I will post the results on here.
Fingers crossed.

[piman]

hello Paul,

at cold start the starting carburettor will overcome any weak setting of the main carburettors which si why I wondered that a cold start was good and hot start was poor. I's a matter of elimination; you can get misleading indications from plugs depending on how the engine state was prior to shut down. There can be several small things that are not quite right which adds up to a non start, which is why eleimination of suspect areas does eventually work.
In the old days, racing drivers did plug cuts so the mechanics could check the mixture, this was done by driving at full throttle and then switch of the ignition and coast to the pits so the mixture could be checked. This gives a better result than coming in and stopping normally. (Weak mixture at full power kills engines.)

We'll see what your mechanic finds in due course.

Alec

[pvsingleton332]

Hi folks,bit of a time getting back to you on my problems.
Had a carb and ignition chap in to look at my problem. He did tests and confirmed i have a faulty ignition coil.
Ordered a new ignition coil over the phone from David Manners group at Oldbury.
Went to fit it today and its not the same size as the old one. Shorter in length, looks like same connections tho.
They sent me a Lucas DLB100, is this the correct one for a Jag MK2 3.8 1965.
If it is incorrect,what is correct one, and would this one be OK.
I did specifically state my car on the phone.
Thanks folks Paul.

[JimboV8]

Perhaps the one you had in the car was the wrong one to begin with. Why not try it once and see if it works.

[B87UL]

Paul

The problem you describe is typical of a faulty Chinese made Lucas replica coil. If you examine the interior, you will generally find the insulation is cardboard or paper and the core is not supported correctly. When that coil heats up the components short out and the spark output can be zero one minute and slightly better the next.

These coils have now been around for some years and quite how killing someone has been avoided I don’t quite know. It appears to me that all the present foreign sourced coils originate in the same Chinese factory. The problem is not confined to England, nor for that matter to Jaguar replacements, I comment from a background in automotive engineering of 60 years, in dozens of countries. They have the same problem, including the USA.

Years ago it was very rare to experience coil failure, now I see it everywhere and often these coils fail in the worst circumstance with no warnings.

You might find it VERY interesting to look up Remax coils (British Made! ) a company that has attempted to eliminate the Chinese faults…………and who I have no connection.

Norman