Engine running on after ignition switch off

[Matt200T]

I have a 1982 2.0 petrol engine car (200T). When I switch off the ignition the engine runs on for a few seconds and finally comes to a stop - usually shaking the car a little.

Does anyone have any idea what would cause this problem and how to remedy it?

 

[paulcallender]

Sounds like your electromagnetic fuel cut-off valve is stuck on. I'm more familiar with fuel injection, I don't know exactly where this valve is on your car, I guess you could locate it by following the fuel lines and finding something valve-like with an electrical connector on it.

 

[guydewdney]

coked up - whats happenign is the head has coke deposits on it - and these are red hot - causing a spark plug like effect.

remedy

1) thash the hell out of it for a few miles (up a long hill?) to clear it out?

2) fuel additive - carb cleaner etc

3) head off and clean

4) check valve clearance etc

5) check ign timing etc

6) clean carb etc

not in that order...

even if tghe fuel cut off is open - why would it still run? theres no spark? so has to be carb engine...

 

[TimN]

Check the timing first. Cheapest thing to do if you have the equipment. A badly tuned engine will have to work harder and will therefore produce more heat.

 

[mercman_1]

Hi
Think Guydewdney is probably right it`s called "Post ignition" and is caused by a buildup of carbon in the cylinders remove the plugs and put a "little" (10-15 ml) redex or similar in the holes so it run onto piston tops then leave for a few hours refit plugs and give it a good run.

 

[tom7035]

I go with mercman on this regarding the 'Redex' treatment. An easy way is to have the engine hot, remove the air cleaner, start up and run at a fast idle. Pour in Redex (or similar) directly through the carburetter air intake until the engine 'chokes' off. Switch off ignition and leave overnight, then give it a good 'Italian tune-up' next day to blow out the c--p from the cylinders.
Be in a well-vented place as it will be smoky!
Follow-up by using a few fl.oz. of Redex to each of the next couple of fill-ups.

 

[paulcallender]

This is known as "dieseling" and is a well known phenomenon. Reducing cylinder temperatures and decoking (the carbon deposits retain the heat) reduces, but does not eliminate, the phenomenon. Diesels don't 'diesel' because they have a fuel cut-off valve.

 

[joe bloggs]

These cars have a solenoid under the carb, the jet is pushed against the needle when you switch off the ignition, this happens for 5-10 seconds, controlled by a small relay like control unit (forget where it is, but post back if you need info and I will find out (tech in a dealer). Idea is to stop the running on that these engines are prone to. Best way to check is to test for voltage at the connector (directly below main carb jet) which should be live for a short time on switching off ignition. If voltage is present apply 12 volts to the valve and see if you can hear it click.

Very much doubt it will need any de-coking, very rare nowdays with modern fuels and oils

 

[Matt200T]

Many thanks to everyone for all the comments and suggestions.

I have a strobe timing gun so I'll check this as soon as I've purchased a workshop manual with all the correct settings. Presumably the Brooklands W123 is the best one to go for?

We bought the car about six months ago and at the time the garage said it recently had a full "top end" rebuild. I assume that this means cylinder head and you'd hope that any coke deposits would have been removed at this time...

I'll also check under the carb for the solenoid...

 

[tom7035]

Hello Matt.
I bought the Brooklands manual (published by Technibooks in South Africa) for my W124 and found it next to useless. Maybe the translation when printed in China was partly to blame! Full of wrong info, misplaced paragraphs, typos, difficult to follow diagrams etc. etc.

My personal opinion anyway.

 

[Matt200T]

Top marks to joe bloggs - my carb has an "idle shut-off valve" underneath. When the ignition is turned off the value closes, preventing the engine from running on.

I tested the value using a lead from the +ve battery terminal whilst the car was idling - the car stopped immediately when current was applied to the valve. I connected a multimeter between the valve plug and earth and turned off the ignition - no power.

I'm now focusing on the idle shut-off valve relay. The manual states "the relay is in the interior behind the lower cover to the left of the steering column". I'll be damned if I can find it though - does anyone know its precise location?