Engine won't switch off

[markleigh]

Recent fault... Car (63 four door saloon) runs fine but when you turn the ignition off and remove key it still runs. Fortunately there's an engine kill switch so I use that! Also... and it may be a coincidence, the ignition light in the speedo no longer comes on. Car starts on the button (or key) but the fault is persistent. Any ideas what to look at first? NB The only things I've done to the car ahead of the fault were fitting a high level brake light and repositioning the windscreen bottle and pump (extending existing live feed). Am sure these are unconnected with the fault occurring! Thanks all!

[svenedin]

When you say the engine won’t switch off when you remove the ignition key do you mean it runs on for a bit and eventually dies or it carries on running completely normally?

“Running on” can be caused by a mixture that is too rich, short journeys and compounded by an idle speed that is too high. That leads to a carbon build up in the head that carries on glowing when the ignition is turned off and then engine runs on for a bit. What you are describing sounds as if the ignition is not being disconnected rather than running on caused by carbon build up.

Possibly the fault is with the ignition switch and the fact that the ignition light no longer comes on might be because it has been permanently on and has blown the bulb. Try a new bulb?

[oliver90owner]

Is this a ‘pre-ignition’ fault or a case of the coil remaining connected to the power supply?

Does this occur even immediately after a cold start?

Does it continue to run indefinitely after turning off?

Simply removing the electrical supply from the coil would easily determine where to look, if you are not sure of the cause/fault.

[markleigh]

Thanks svenedin and oliver90owner... the engine carries on quite happily as normal so I don't think it's carbon build up... saying that I'll check the plugs later! My inclination is that it's the switch... exploration awaits. Many thanks!

[Sleeper]

" Fortunately there's an engine kill switch so I use that! "

What does this " kill switch do? Remove the 12V from the coil ? disconnect the points?

Could be a clue...

John ;-)

[simmitc]

Agreed, the kill switch - If it interrupts the supply to the coil. then from where does it get its supply?

Do you have a meter to measure voltage and continuity? It can be very useful for fault finding.

[markleigh]

Simmitic, Sleeper... kill switch was on car when I bought it. AFAIK it interrupts the coil... but armed with this clue I'll investigate, What's odd is that it suddenly happened. Can't investigate for couple of days but will post my findings. Thanks!

[Bill_qaz]

Perhaps the kill switch as you call it was an immobiliser theft deterrent fitted by previous owner. Now your ignition switch is staying closed, when you key off is there still voltage to the kill switch?

[markleigh]

All remedies draw a blank! Auto electrician due next week. Will advise on his findings!

[kevin s]

Have you added a relay to carry extra ignition loads?

If so the voltage can back feed via the ignition light and keep the relay engaged, a diode in the circuit cures it.

[geoberni]

All remedies draw a blank! Auto electrician due next week. Will advise on his findings!

I've no doubt it will be something simple and easily found by a competent user of a multimeter.
I suspect a faulty Ign Sw, or some additional circuitry a past owner installed is now playing up.

I bet they find it within 5-10 minutes.

[markleigh]

Sorry for late reply! You were right. Some bodge work from previous owner was the culprit. All good now! Thanks.

[geoberni]

Sorry for late reply! You were right. Some bodge work from previous owner was the culprit. All good now! Thanks.

That's only half an answer, what/where did they bodge?
You never know, someone else might encounter the same bodge (plus I'm a retied Lecky so I'm curious.. .)

[Sleeper]

Ditto.

John ;-)

P.S. I had that.... The voltage from the alternator was feeding back to the excite wire, had to install a kill-switch.... changed to a diode.

[markleigh]

Ahhhh. I will have to consult the auto electrician... he found it right away - it was an easy fix... but I'm not sure what it was as I was gaping at him like Caatweazle as he performed his electrickery. Will ask him and report back!