4.2 running on

[Marcus2571]

I have a 4.2 engine with electronic ignition, flame thrower coil, and running triple SU's. I always use super unleaded and the engine runs at normal temperature.

Of late I have had an issue with the engine more often than not running on when I switch off. This is always when the engine is hot following a long run and for about 2/3 seconds. My initial thoughts were that I was running lean, so I richened the mixture and the plugs are showing it to be OK. I've got no other signs of running lean - such as poor/lumpy acceleration, misfire/uneven running etc.

Could it be timing or an ignition switch issue?

Any help gratefully received.

[malcolm]

Badly carbonated head potentially?

[christopher storey]

It is essentially a sign of some form of localised overheating, or , just possibly, significantly over-advanced ignition timing . The first thing I would do is remove all the plugs and look at each one carefully . What you are looking for is excessive carbon deposition, whiskers on the electrodes, and most potently blistering of the insulator on the central electrode - if this is present then it is strong evidence of detonation in normal running , which is likely to cause engine failure in the form of burning holes in pistons . Check that the plugs are the correct grade and type - most people now use NGK BP6 ES I think, or the Bosch, Beru or Champion equivalent . If the plugs are being cooked , then after checking timing etc a change to a colder grade may help

Edit: having read the other post on plug selection today, I see some people use BP5ES which is I think a grade hotter that BP6ES

[Heuer]

If you have an aftermarket fan you may find it is providing a reverse feed to the coil even with the ignition switched off. You could try disconnecting it and see if you still get run on. If it is the cause a diode in circuit is the fix.

[jag68]

Marcus when you say the car is running on do you mean it just keeps running for a few seconds when you turn the ignition off, or is it dieseling - that is it runs very rough and bucks, and can do so for up to a minute. I've had a dieseling problem on mine and can perhaps help you.

Terry Sturgeon