Run on

[MJ41]

I have a 2000 Penta 4.3 Volvo sx that intermittently runs on (dieseling) after turning off the igntion.
Any thoughts as to why?
Many thanks,
Mark.

 

[rbh]

Re: Run on

make sure your plugs are not fouled up, timing is on, and if it only "runs on" after a hard run let it idle down before you turn it off, possible overfueling.
rob

 

[lowkee]

Re: Run on

The run-on is caused by heat (it makes the spark plugs mimic diesel glow plugs, hense 'dieseling'). Like rbh mentioned, if you are getting the problem after WOT, let it idle for a minute or so first. If it happens quite often even at idle, you may have water flow issues (bad impeller or water pump) and the engine is overheating. Remember, with carb engines the fuel is delivered every time the engine turns over, no matter if the key is on or not, which is how dieseling happens so easily with boat engines and never with newer cars.

 

[dontask]

Re: Run on

Before you are sent chasing your tail there is a service bulletin for the Mercruiser 4.3 run on. It might help with your set up & it was provided by one of the Mercruiser trained guru's here on this site. I had a "run on" issue with my 4.3 and the service bulletin provides steps to eliminate this issue. I believe the # is 97-17, which is at the top left hand part of the page.

 

[MJ41]

Re: Run on

Thanks,
How do I get to the service bulletin?
Mark

 

[dontask]

Re: Run on

Thanks,
How do I get to the service bulletin?
Mark

Ok I had to find it for you the hard way. If someone does not post it directly here for you then Google this "4.3 Mercruiser run on service bulletin". It came up right away---first hit which was an Iboat response with DonS supplying the link. Let me know if it worked for you.

 

[MJ41]

Re: Run on

Yes, it did thanks, and thanks to all who've helped out. I'm going to the lake this Sunday so I'll try to figure it out then.
Mark.

 

[jkust]

Re: Run on

Since I had this issues when my Mercruiser was nearly new, I will comment. The two things I did to fix my run on were:
1. let the engine idle for a 30 seconds or so after stopping, then shut down. No more run-on
2. Started using 89 octane and never had to do the above again.

Accidently mixed 87 octane with a half tank of 89 last fill up and got a brief second of run on if not doing number 1. Conclusion, 89 octane cures it.