What causes an engine to continue to run on when ignition is switched off?

Question

the engine is a volvo penta 4cyl petrol,it starts up first turn of the key when cold but once its been run for half an hour it runs on when the key is turned off,it also takes a bit off starting after its been switchedoff for 5mins if its warm,i tried a timing light on it and its showing no one cylinder firing about 15-12 degrees before TDC on tickover at 650rpm,i have had the carbs serviced by a marine engineers(off the engine) and all jets etc were replaced,the mixture screws were set to the spec in the volvo workshop manual,ie 8 full turns out from seated,this engine has cost me a fortune now and its becoming a real headache,any ideas would be much appreciated,its exact spec is 1991 volvo penta 250 4cyl 146hp,its fitted with the later type solex carbs and has contact breaker ignition.

Answer 1

This used to be known as "pre-ignition" and was caused by the ignition timing being too far advanced.   Slacken the distributor clamp,r****d the timing,retighten and try it.

Answer 2

this minor annoying problem is called "dieseling".which means the whole problem is in your distributor. not the timing but the dwell. your contact points are improperly set. change the points and correctly gap them (the dwell on a meter)and your dieseling problem will go away.

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Answer 3

timing is out contact breaker needs renewing aswell

Answer 4

If it has vacuum advanced and r****d this is probably the problem check the distributor is moving it's full travel

advice from sweeties hubby hope it helps x

Answer 5

Ignition timing

too far advanced..

Answer 6

Well I would reckon that a 1991 petrol engine with this problem is suffering some coke build up in the headspace above the pistons and when the coke gets hot after running, it acts a bit like a spark plug and keeps firing even after the ignition is switched off.  Ideal fix is to take the head off and do a "de-coke" as used to be done on old cars for same reason.  You might be able to reduce coke with some petrol additive over time but it all depends if you want a cheap fix or a proper fix.

Answer 7

This motor is based on the GM 4 cyl engine, as is the Mercruiser 3.0L.  They are notorious for running on.

Try a slightly richer setting on your idle mixture s***w or you could try running it on premium unleaded rather than regular unleaded.

Answer 8

It has nothing to do with timing. The idle RPM's are fine also. It is in the ignition switch or the black and yellow kill wire.

Answer 9

It could be that the spark plugs are not the correct ones.

Every engine has a spark plug of a specific heat range. If the installed spark plug is too far toward the hot end of the heat range(too hot) then the engine will run on after you switch off and can be problematic to start after a short shut down period (Heat soak) .Also the engine may be detonating under load which will eventually cause serious damage.

If the spark plug is too cold then cold starts may be a problem, the plugs will foul up easily and the engine will start to miss fire. But that's not what you got.

So go to the Volvo dealer with one of your spark plugs and ask him if the heat range of the plugs are correct. If they are not the brand recommended then there is a possibility there was a mistake made cross -referencing and you got the wrong heat range .

All spark plug manufacturers produce a spark plug reference book that has listings of all the engines they have made spark plugs for.I would try to get my hands on a NGK book first, if not them ,then Champion ,then Bosch .Europeans like Bosch and your engine is European so its worth a try. See if your engine is listed and select the correct plug . Also Try  the web sites for the right plug  it will probably be quicker and easier.

Answer 10

your timing is slightly out

Answer 11

If your engine is actually running after turning the switch off, by that I mean running just as if you never shut it off, you need to check and make sure all wires are connected to the ignition switch. If they are, replace the ignition switch. The kill circuit in the switch is bad.

If it's dieseling after shutting off the switch, your timing is advanced a little too far or the engine is overheating. Both will cause dieseling and hard, slow turn over of a warm engine.

Answer 12

Timing is out.

Answer 13

timing is advanced too far.  back it off just a tad....

Answer 14

for it to run on,suggest the timing to be too advanced , does it have a vacume advance set up?.this would also course this to happen

Answer 15

replace your ignition switch, it is could be bleeding current through, i am sure you have a book- check the ohms readings on your ignition system, usually these problems are a pain and take time, but stick with it you will find the problem

Answer 16

I would suggest that it may be running too fast when you turn it off. I do know the specs., but if it is idling at 650 RPM than seems awfully fast to me. I think around 400 would be more like it.