Engine keep runing after turn key off

[FLboat]

HI Guys ... This could sound funny but it is true , After I turn the key to stop the engine this keep running for like 30 sec . if you turn the key on it just keep running like nothing ,

By the way after this happens Idle speed is a little high or doesn't shift on idle , In other words it goes from forward to neutral , so there is no idle

Engine is a Volvo penta 4.3 with a SX drive.

All help will be appreciate Thank you

 

[intrepidvoyager]

Re: Engine keep runing after turn key off

This in red from MERC

My engine diesels, or runs on, after it is shut off. What causes this and can it be eliminated?
Under certain conditions, carbureted engines may "run on" after the ignition key is turned off. This condition is rarely caused by a defect in the engine itself. Usually, a combination of external factors is responsible. These factors include, but are not limited to, the type and formulation of fuel used, the boat's engine compartment ventilation system, ambient air temperatures, excessive engine compartment temperatures, how quickly an engine is shut off after running at cruise or higher rpms, elevated engine idle rpm setting, use of spark plugs with an incorrect heat range, deposits on the spark plugs or in the combustion chamber, etc.

There are some things you can do to minimize a "run on" condition. Most importantly, allow the engine to idle for a few minutes before shutting it off. This helps the engine to normalize at idle rpm. Other suggestions include having your dealer verify the engine idle mixture, idle rpm and timing are correct. Try a different brand of regular fuel or try premium fuel. Use spark plugs that are in the next colder heat range.

my experience with run on ...... carbon build up ...pull the plugs and have a look ..... also you could run with the engine compartment open and see if that makes a diff ..... I once had a Trojan with a 350 CID with this problem ..not carbon .....ended up putting ventillation fans in the engine compartment.

 

[arfaname]

Re: Engine keep runing after turn key off

For run on to occur you must provide unassisted ignition. The key is off so the power to the coil is off and therefore no spark. It must be getting an ignition source from somewhere. I would suggest you look at plug temps or carbon build up and check your timing both static and at revs. Your advance system may be sticking if mechanical hence your high revs at idle. There are products you can add to your fuel to clear carbon buid up.

 

[Don S]

Re: Engine keep runing after turn key off

While carbon buildup in cars is quite common, it's not a real problem with boats. simply because they don't get the hours, temps, and conditions a car or truck does.
In boats, it's typically an idle rpm being too high, or when it's shut off immediatly after a hard run. These are the problems in about 90% of the cases I run into during the summer months.
Here is a Mercruiser service bulletin that explains the reasons for marine engine dieseling and run-on. While you may have a Volvo, it's still a Chevy engine and the same info applies.

Here is the bulletin
http://www.4shared.com/file/53242775/d72d01/Engine_Dieseling_or_Running_on.html

 

[FLboat]

Re: Engine keep runing after turn key off

Thanks for all your help . I'm now pretty sure the problem is caused for the high idle , around 1500rpm and this is caused by a bad cable ,

Also Im considering that temp go high around 200 when you hard run for 10 min or so .This may be caused by a worn impeller which was destroyed and the pieces could be blocking some passages ,

Any recommendations where to look for the pieces . By the way I did blow air tru the exhaust hoses and they looks clear , t-stat cover clear too , Also I did connect the water hose from the engine to the drive and water flow easy . Any recommendation appreciate . Thank you :

 

[Don S]

Re: Engine keep runing after turn key off

I'm now pretty sure the problem is caused for the high idle , around 1500rpm and this is caused by a bad cable ,

No wonder it won't shut off. You've waited long enough, replace the cable.

Any recommendations where to look for the pieces .

Yeah, right hear at iboats. Look just above your original post. Volvo Penta Parts would be my suggestion.

 

[arfaname]

Re: Engine keep runing after turn key off

Hey Don, not in any way doubting what you say but I'd like to understand how the high idle effects run on. What does it use as an ignition source? Would this not suggest that if I shut my engine off at 4000rpm it will just run on?


Oh and as for looking for the pieces, I think he meant pieces of the impeller??? The shredded bits..


I think..

 

[love1u0]

Re: Engine keep runing after turn key off

Give this a read arfaname......

"An idle speed that is too fast can leave the engine with too much angular momentum upon shutdown, raising the chances that the engine can turnover and combust more fuel and lock itself into a cycle of continuous running."

http://en.wikipedia.org/wiki/Dieseling

 

[intrepidvoyager]

Re: Engine keep runing after turn key off

usually you find pieces of old impeller in the raw water line on the RWP side of the power steering cooler or oil cooler if you have one ... unclamp the outlet hose at the RWP and the pump side of the cooler and check the hose and also make sure there are no pieces wedged in the cooler intake ....simply back washing the line may not get them all out . I have seen pieces actually stuck in the cooler tubes ....

If you don't know the age of your impellor ...change it for new .

Ya ... 200 is way to high ....but guages are notoriously wonky ...so try this

http://www.acms-usa.com/bulletin_files/hotItem.htm

If your risers are way over 140 ..temp you can hold your hand on ......start looking for other cooling system issues

hopefully a new impeller will do the trick ....

IF MY BOAT I WOULD NOT RUN THE ENGINE AGAIN WITHOUT A NEW IMPELLER
......AND CHECK AS ABOVE FOR OLD IMPELLER PIECES.

As Don said high RMP's .....but now you have added really hot engine I think that's case closed.

 

[FLboat]

Re: Engine keep runing after turn key off

Thank's to all for your help... Already fix the idle issue . just pump oil intro the cable and adjust the idle on the screw and all came back to normality .

I will check for the old impeller pieces on the weekend .... And yes I did replace it with a new one but didn't check for the old impeller and after that I got the problem with the high RPM overheating

Thank's again for your help

usually you find pieces of old impeller in the raw water line on the RWP side of the power steering cooler or oil cooler if you have one ... unclamp the outlet hose at the RWP and the pump side of the cooler and check the hose and also make sure there are no pieces wedged in the cooler intake ....simply back washing the line may not get them all out . I have seen pieces actually stuck in the cooler tubes ....

If you don't know the age of your impellor ...change it for new .

Ya ... 200 is way to high ....but guages are notoriously wonky ...so try this

http://www.acms-usa.com/bulletin_files/hotItem.htm

If your risers are way over 140 ..temp you can hold your hand on ......start looking for other cooling system issues

hopefully a new impeller will do the trick ....

IF MY BOAT I WOULD NOT RUN THE ENGINE AGAIN WITHOUT A NEW IMPELLER
......AND CHECK AS ABOVE FOR OLD IMPELLER PIECES.

As Don said high RMP's .....but now you have added really hot engine I think that's case closed.

 

[Don S]

Re: Engine keep runing after turn key off

Already fix the idle issue . just pump oil intro the cable and adjust the idle on the screw and all came back to normality .

That is a temporary fix at best, and won't last long. You need a new cable.

 

[intrepidvoyager]

Re: Engine keep runing after turn key off

forgot ....re your cooling system ...also make sure there is no marine growth blocking the sea/lake water inlet holes on the lower unit of the outdrive. Here just for reference is how a typical system works

For example the circulating pump on a standard small V8 GM based engine will flow approximately 50 gpm through the engine. The typical raw water supply pump is capable of flowing about 18 - 20 gpm depending on the gear ratio and restriction the system experiences. A standard 300 Hp small V8 engine dissipates approximately 300,000 Btu/Hr of heat into the coolant. To maintain a thermostat temperature of 160 degree F at wide open throttle this engine would need a pump to flow about 8 gallons per minute (GPM) of 70 degree F water into the system to maintain this engine temperature. Since the Alpha raw water pump can flow 18-20 GPM there is significant bypass (excess) water supplied, which therefore has to be dis-charged somewhere.

In a cold manifold system the warm water that flows through the thermostat, as well as this excess bypass water are joined together in the thermostat before exiting and being introduced into the bottom of the exhaust manifold. The fact that your are mixing together a lesser amount of 160 degree F engine water (8 GPM) with 10+ GPM of cold lake water allows the aggregate coolant temperature in the manifold to fall below the 110 degree F threshold needed to prevent the accumulation of condensation in the exhaust system.

.... a handy tool to have to be able to check your cooling system on a regular basis is an IR thermometer ...about $40 ....

 

[arfaname]

Re: Engine keep runing after turn key off

Thanks for the link love..

I have pulled this quote from it however and agree as such.

"The dieseling phenomenon occurs not because the compression ratio is sufficient enough to cause auto-ignition of the fuel, but a hot spot inside the cylinder starts combustion. An automobile engine that is dieseling will typically sputter then gradually stop, probably because of an electrical fault"

So whats causing the hot spot? I understand your point on angular momentum however there still must be an ignition source be it spark, hot spot or something else.

So if there is a redundant ignition source at just above idle which is pre-igniting the fuel, would this not be apaprent at higher revs and cause knocking/pinging?

I debate this only to understand the phenomenom.

I agree on replacing the impeller. Its a critical part of your return journey.
I also agree your cable is shagged and needs replacing. Not expensive items in the scheme of things.


Thanks.

Sean

 

[FLboat]

Re: Engine keep runing after turn key off

I agree with you , The oil on the cable was only a temporary fix however it will work for a couple time before I use boat again and get me time to repair the overheating issue ,
Im gonna start this weekend checking all water passage . first time it gets overheating was very high but I did turn it off right away do, after that I'll be checking the temperature on the engine and exhaust and none gets hot unless high RPM . Do you think I could damage the exhaust if so where to check .
Thank's a lot

 

[Simoniz]

Re: Engine keep runing after turn key off

My boat used to do this (mercruiser 3,0l) unless I let it idle for 30 seconds before shutting down.

When I replaced the impellor, it never happened again, ie worn impellor not pumping enough water allows engine to run too hot therefore allowing carbon deposits in combustion chambers to glow, thus causing running on.

 

[Dunaruna]

Re: Engine keep runing after turn key off

Also, given the symptoms, prudent to check the base timing.

 

[FLboat]

Re: Engine keep runing after turn key off

Ok Here are the results .

Idle was very high(1100 rpm ).Cause a corroded cable and that was the cause of the run on engine

Overheating was cause the two small hoses from the t-stat cap were clogged with old impeller pieces .

I hope the next try everything will be ok .

By the way due to the high overheating I guess there is something wrong with the flappers ,I found some around the exhaust , what will cause to run it like that .

Thank you

 

[Bondo]

Re: Engine keep runing after turn key off

what will cause to run it like that .

Ayuh,.... like What,..??....

 

[Don S]

Re: Engine keep runing after turn key off

Assuming you mean "what will happen if I run it without flappers", you really don't have a choice. Volvo quit using them in the SX series drives.
Here is the service bulletin that explains it.

http://www.4shared.com/file/51149475/c49b77de/Volvo_Exhaust_Flapper_valves.html

PS, Do remove the old ones, don't just let them lay in the exhaust pipe or partial pieces in the Y pipes. They can break off and plug up the exhaust and cause very poor running.

 

[FLboat]

Re: Engine keep runing after turn key off

Thanks guys for all your help , Im sorry about my English isn't my native language .(like that) yes I means without the flappers ....
Ok now I hope everything runs smooth and Thanks Don s for the link .

I will post as soon as I give a try