Running on after engine switched off

[RichT]

Hi all

A little help on this would be appreciated

My 3.4 auto mk2 has started to run on occasionally when swited off after a run usually switching off in drive so the revs aren't boosted helps to stop this

I have looked at the timing using an inductive gun on lead 1 (cylinder near bulk head) and the timing looks to be 6-7 degrees advanced before tdc I have not checked whether the timing marks aaon the pully are real but physically checking tdi, if I was to do this do I go in cylinder number 1, some help with other checks would be good I havenet really started yet but I have fished a couple of plugs out and they look clean but haven't chked them all, also I guess I should check fuel mixture, I have an air fuel meter


All info especially advance settings would be helpful I am running unleaded fuel and a 123 ignitor system which is about 3 years old

Cheers

Richard

[J44EAG]

This in a nutshell is what I was taught at aero college many years ago.

http://www.google.co.uk/url?sa=t&rct=j& ... GU&cad=rja
http://www.google.co.uk/url?sa=t&rct=j& ... 5273,d.ZGU

To cure, I would be retarding the ignition a little and perhaps add some octane booster to help anti knock issues.

Mike K

[RichT]

Thanks Mike I will try that retarding it by a degree or so

Cheers

Richard

[piman]

Hello Richard,

is the car running hot as this can contribute as can a too high idle speed. Automatics should idle at 500 rpm if my memory is correct? Another check is that the correct grade of plug is fitted.

Alec

[RichT]

Hi Alec

You probably noticed my post re overheating from before,

This seemed to be an isolated problem in the summer so I have not got round to flushing the waterways out and then installing my shines new kenlow fan

The temp does go up a bit when standing idling after a run idle speed is steady at 500 but sometimes runs on even if the engine is killed straight after stopping. this is an intermittent thing.

Why does increase heat cause increased rpm?

I think I really need to check that my tdc marks are in the right place (I take it i have to do this in no1 cylinder)

My gut feeling is that I should start with ignition first (although I guess I should check plugs first and although scared look at valve clearances) before messing about with carbs

There seems to be a lot of chat on here re 123 ignition systems it would be nice if we could have an article on setting all this up to summarise all this knowledge (anybody please feel free to jump in here if there is one in the archives)

Cheers

Richard

[piman]

Hello Rich,

my feeling about timing and setting to a specific figure is only a starting point and road testing is the way to set to optimum. I aim to advance the timing until the engine pinks then retard a bit so it doesn't. This should give the optimum setting. You can then check the actual timing and retain that figure to use for future adjustment if you like.
Another point is how well the distributor is working, with more and more people using electronic 'no maintenance' systems, forgetting that the distributor needs mechanical maintenance, i.e. lubrication and checking the mechanical and vacuum advance is working correctly.

I don't really know why temperature should affect idling speed.

Alec

[Martec]

Hi Richard,

My dad was an old fashioned mechanic and always said set the car up to manufactures setting and then see what is getting upset.

This consisted of:-
Plugs
points
Tappets
timing
and carburrettors

Due to unleaded burning faster than the manufacturers setting on leaded fuel (lead was a flame retardant) reduce the timing advance by about 3 degrees from the book setting.

It used to be a service included new plugs, points and so the timing needed resetting, and moves as the points burn and the heel wears.

Once you have set everything up correctly then you can go fault finding.

Best wishes

Brian

[RichT]

Thanks for your replies gents

Hopefully I will get a chance to look at this on Sunday

So far I have learnt that the tdc mark corresponds to number six (front) cylinder which is handy so first place is to check tdc mark (yellow sploge) from previous owner is correct I think there may be a 5 degree btdc mark also.

I will endeavour to work out and make some better degree marks so I can set the dynamic timing better

The distributor is even more of a pig to get at on account of a non std fuel filter being in the way, I have checked the vaccum is working ok as Alec suggested.

I will try some higher octane fuel but I suspect Brian is right the timing prob needs to be retarded a bit to stop running on and I need to methodically go thru all the points mentioned

As an aside I have found keeping the dashpots in the su carbs topped up is important for smooth idling but I have found the blue manuals oil grade recommendation leads to rubbish throttle response, I use atf same as gearbox which seems to work well

Cheers for now

Richard

[piman]

Hello Rich,

I don't know what equipment you have, but a simple way to check TDC is to use an old spark plug and destroy the ceramic top so that a longish bolt will then pass through the body. The aim is to get two marks on the damper before and after TDC by rotating the engine up to the fixed stop outlined then half the marks to give an accurate TDC point. Obviously care and accuracy is required in this process.

Off hand I don't know what the blue manual gives for dashpot oil specification but S.U. specified S.A.E. 20 grade oil, although I always used engine oil (20/50).

I remove the distributor to maintain and check it. The 6 cylinder Aston has it's distributor in a much nicer position from that point of view (direct drive off the rear of the camshaft), especially with a front hinged bonnet. They also specified setting the timing at above 3,000 rpm, which was full mechanical advance, which in a round about way proved that the advance mechanism works.

Alec

[RichT]

Hi Alec

That's a really good tip just to clarify would I be rotating the engine in both directions and taking the average between the two

Cheers

Richard

[Martec]

Hi,

Alec's suggestion is the simplest for finding TDC and yes you move the engine from side to side of TDC until it hits the probe and mark it on the bottom pulley, divide by two and that is TDC, then you can make up a permanent mark or move the original mark until it is now accurate.

This may be of use to you for the spark plugs:-

http://www.ngkpartfinder.co.uk/car_comm ... engine=3.8

I couldn't find MkII so used the 3.8 E type, I use the Iridium version of this and it is lasting well against the LPG so will do nicely for petrol (Ebay has been cheapest so far).

You could always ask 123 what map they recommend for your engine.

Brian

[piman]

Hello Brian,

"You could always ask 123 what map they recommend for your engine."

I would do it the other way, tell them the Jaguar's curve and ask if their unit has a match. From what I remember they only have 16 curves so the chances are very unlikely that it will. They do a fully programmable one I believe but for a lot of money and it is not warranted in my view?

Alec

[Martec]

Hi Alec,

The distributor and advance curve is a bit of a problem, Mine is a 1961 and so had a Lucas DMBZ dizzy, I reconditioned it and although a little worn was rubbish. I asked Ken Jenkins about it and he said it was not good when new! I had a lucas D25 set up to suit my engine and axle and the setting was brilliant (top gear at 500 revs, stamp on the accelerator and it took off, the DMBZ would fluff).

So it is debateable if the original settings/curve was ideal, Petrol and ideas change. As you know I have gone the whole hog and use a coil pack and ECU for the dual maps, but a well set up Dizzy with a decent curve is still good for just petrol. I still have my Dizzy in place as a back up and must do a practise run at changing it over.

If I had a 123 Dizzy I would enjoy experimenting with the 16 maps to see what it would do.

Brian

[piman]

Hello Brian,

the manufacturer spent a lot of time and effort setting the distributor to suit the engine so the original curve is best, unless you have a fully programmable electronic set up and a fortune to spend on a dynamometer. Petrol has changed but it is the engine characteristics that determine the burn and hence the curve. The timing figure may need adjustment from the 60s but the curve essentially remains. Over the course of time distributors get replaced often with similar types e.g. 25D6 but of the wrong specification.

The reason I say only sixteen is that, for instance, Triumph had nearly as many variants for the Triumph 2000 saloon range only, and of those 16 curves only three or four will have the correct total advance. It is easy to select an excessive total advance and as it is undetectable when driving there is the possibility of doing damage to the engine.

My personal view is that I prefer to stick with the original and have it overhauled and re calibrated.

Alec

[RichT]

Hi all

As an aside to all this drove car all weekend after filling with some super unleaded and it never ran on once!

I will still have a poke about when I get time (rather than driving it all day ) a bit of retardation is still prob in order

Although the phrase if it ain't broke don't try to fix it is burnt into my brain from previous misdemeanours


Still chance favours the prepared mind......................................

As for electronic distributors I love em, no points or condenser to worry about and a circuit that prevents coil overheating, a good friend of mine hates then, but then again he is in the habit of meddling and connecting random wires and fried his optronic unit the other day

Cheers for now and thanks for all the tips


Richard