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Engine Keeps Running When The Key Is Off And Out Of The Ignition.


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#1 Ado1379

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Posted 19 January 2020 - 09:48 PM

1992 Mayfair, no haynes manual to hand, they are both at my dads so some help would be appreciated.

 

Before i start fault finding i just wondered if anyone has ever had this before? 

 

Before ignition is engaged, no key in the car and you can apply the indicators (i know this shouldnt happen until 2nd click on the key) 

Turn the car on and it starts up fine, nothing out of the ordinary until you go to turn the car off. it just keeps running. I have a digital voltmeter as part of my dash setup and when you turn the key off it goes from 13v (its low as i need to get around to replacing the fan belt) to 11.8v or there abouts. 

 

Am i right in guessing that when the key is in the 'off' position, it takes away the 12v feed to the '+' of the ignition coil? 

 

thanks guys



#2 phillrulz

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Posted 19 January 2020 - 10:03 PM

Yes the key should remove the 12v feed, since the volts drop from 13 to 11 sounds like its run on as the engine revs drop so the alternator doesnt provide the 13v. 

 

Guessing its a slow lumpy idle not a normal 850-1000rpm idle 



#3 Ado1379

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Posted 19 January 2020 - 10:10 PM

thanks for the reply. I was originally thinking that could be the problem.... but that wouldn't explain the indicator problem. She is running very fuel heavy. adjusting the carb is one of my jobs to do this weeked. How long roughly would 'run on' occur though? this will actually carry on until I either stall the car on purpose or disconnect the ignition coil



#4 MrE812

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Posted 19 January 2020 - 10:43 PM

Almost sounds as though the ignition switch is shorted allowing power through to position 2.

You'd be best to check the ignition switch with a multi-meter but you could use one of those "light-up" screwdriver tester thingies instead.

if you had another one lying around it would be quick enough to swap it out.

The volt drop is odd - if the engine is running the alternator should still be giving a charge.

Hope you find the cause - let us know.



#5 Ado1379

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Posted 19 January 2020 - 11:12 PM

The ignition switch is brand new, long story short someone stole the keys which had the immobiliser and everything on. Without going in to too much detail about my new security on the car I’m doing Some re wiring. New ignition barrel as of yesterday. I’ll get to the bottom of it eventually.

#6 andyapanel

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Posted 20 January 2020 - 08:34 AM

Buying a Haynes would be a good first step.

 I would suspect a very lean mixture, causing it the running on.

The voltmeter reading does not sound unusual when the ignition is off; does it read 11.8 before firing up the engine?

The poor fuel consumption could be associated with a weak mixture.

Have you got an anti run on valve? It could be sticking.

Try adjusting the carb mixture to make it a bit richer. If it IS weak, you may hear the engine "hunting"-the revs rise and fall

Anyway, good luck and I hope you fix it soon.



#7 Ethel

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Posted 20 January 2020 - 08:58 AM

Just unplug the ignition switch to see if that stops it.

If it doesn't you're looking for where permanent live can short in to the ignition, fusebox, solenoid if you have ballasted ignition. It could also be an alternator fault, but you should get some indication from the ignition light

#8 nollyd

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Posted 20 January 2020 - 11:31 AM

Had this once on a mg metro,turned out to be a hotspot in one if the bores.same as you,key out,dont know how fuel etc got there but if you find out please let us know.

#9 Ado1379

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Posted 20 January 2020 - 03:01 PM

FOUND IT!

So basically my car also has a leisure battery fitted to power all my ancillaries, connected to a voltage sensitive relay so the alternator can ‘trickle charge’ it. Basically what had happened was the leisure battery powers the stereo but when I re-wired it the other day I used the ignition coil to provide a switched live. The leisure battery was basically shorting our the ignition coil so the car would just keep running...

You live and learn! That should be the motto of my life




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