Engine running-on when switched off

[gouldsborough7]

My new car has a Cortina Pinto 2000 with a 'leaded' head (squirt a Castrol super goo into petrol tank on each fill-up). A previous owner fitted a carb from a 3 litre Granada, and I think a Piper camshaft (don't know what model or stage of tune). It also has a bolt-on Mobelec 130 electronic ignition package if that rings any bells with anyone.

The problem I want to fix is that the engine sometimes 'runs on' for 5 seconds on so when I turn it off. No obvious cause. Spark plugs look sooty if anything, and no symptons of overheating. Any ideas guys?

[danny_nelson]

Re: Engine running-on when switched off

Hi Mike, there are a number of causes, some of the most common are, using too low a grade of petrol or the wrong grade of sparkplug, incorrect ignition timing, to high an idle speed, an excessive build up of carbon in the combustion chambers, or in some cases plain old fashioned engine overheating through any one of a number of its own causes. Large capacity four cylinder units with highish compression ratios seem to suffer most, but any engine can be afflicted by this highly irritating phenomenon at some time or another, particularly if its running on a lean and hotter burning fuel air mixture. What is happening when you switch off something in the combustion chamber continues to glow red hot, or at least still hot enough to ignite any remaining petrol air mixture. That something could be, a sparkplug, the edge of a valve or small pieces of carbon. This makes your engine behave not unlike a compression ignition or diesel engine. So that is the causes I am sorry I could not explain it in less words! What can be done, first the Castrol unleaded that you are using try the product that gives an octane boost if you are not already doing so. Make sure the engine is in an optimum state of tune. Let the engine idle for a few seconds before you switch off. Sometimes what works quite well is flooring the throttle immediately after switching off the ignition. If all else fails you can fit a solenoid controlled valve. This can be a valve which opens to allow air into the inlet manifold on engines withvariable jet carbs. On engines with fixed jet carbs the valve is in the idle circuitwhich, as you switch off the ignition cuts off the flow of petrol up stream of the jets and kills the engine There was a company in Plymouth Tecalemit Ltd on the Belliver I ndustrial Estate, Roborough Devon Pl6 7bw. They did not do retail but Pat Bedford 0742 670162 use to quote and take orders. If you can not solve the problem I can give you more contact details.

[gouldsborough7]

Re: Engine running-on when switched off

Thanks very much Danny for providing so much detail. I'll try your various suggestions, and let you know the outcome.
Cheers
Mike

[gaddbrose]

Re: Engine running-on when switched off

Hi Mike ref. your over-run on the Pinto. I agree with all the reasons that Danny has given, but there is one not mentioned that I experienced with my old engine and that's the cam. You mentioned a Piper cam has been fitted, but you are not sure of its pedigree, If its a "hot" cam put in for performance it will probably have a fairly high lift on the valve and consequently the opening and closure of sucessive valves will overlap, so in one cylinder a closing valve will match an opening valve in the next, and the gasses will tend to flow from one cylinder to another.I dont think a combustion takes place, its just the inertia of the final ignition operating thro. partially opening valves that continues to push the engine over. Also, a "hot' cam will give you a poor tick over at the normal 800 r/m. It runs very lumpy, and is best at 1200 or so. If that's the case then your cam is a few steps up from standard. Given that you have a decent cam , that carb. and a gas flowed head, you should expect to get about 125 hp from it instead of the 95 -100 on the unmod. version. regards Brian

[b_caswell]

Re: Engine running-on when switched off

Another reason can be if the rad fan is running when you turn off the ignition. It can self dynamo and produce enough juice to run the engine

[gouldsborough7]

Re: Engine running-on when switched off

Progress report -
1) I replaced the spark plugs, as I was unsure of their history,
2) various adjustments and checks on carb and ignition made no real difference to engine running - it ticks over at around 1000rpm, with a slight lumpiness, but picks up without hesitation when accelerator is pressed,
3)tried on several occasions flooring accelerator after ignition key is turned off - resulted in dramatic backfire - not good idea in Tesco car-park!
4) tried to contact Tecalemit Ltd, but they only deal with the trade.

My current thoughts that the combustion chambers might just be sooted-up, and something is glowing after engine is shut down, sufficient to get the diesel effect. To add weight to this - the running-on only happens after engine is thoroughly hot.

Running out of ideas now, so any other help would be appreciated.
Cheers
Mike

[csjcarolyn]

Re: Engine running-on when switched off

Your engine idle might be too high at 1000 Rev/Min., should be 750 I think, this might cause running on.

If your combustion chambers are carboned up you can buy a chemical which you pour part into the fuel tank and part in through the air intake with the filter off. I have used this and it can restore compressions as well.

[Dane_Rescueman]

Re: Engine running-on when switched off

you can also try the aqes old remedy. When engine is warmed remove the plugs. Pour a tablespoon of REDEX into each cylinder. Turn the engine over a few times, without starting, to spread it around. Leave it overnight. Replace plugs the next morning and start. You will experience a dense white exhaust for a couple of minutes but some of the carbon will have been loosened and expelled. If nothing else it will amuse the kids!
Good luck.

[johnsr]

Re: Engine running-on when switched off

I recently fitted a 70A Escort alternator from a breaker. Sometimes when the ignition is switched off the ignition warning lamp does not extinguish and the engine continues to run. It looks like a diode is playing up and while this is happening it is delivering current which is sufficent to power up the ignition ECU and the engine continues to run. On other occasions the bulb does extinguish and the engine come to a stop in the normal way.