4.3 Cobra sputtering after key turned off

pappysc2

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Jul 5, 2007
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I am having an issue with my 4.3 cobra of the engine wanting to keep running/ sputtering after the key is turned off. Wondered if you all could help?Thnx
 

Don S

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Re: 4.3 Cobra sputtering after key turned off

It's called dieseling. Get the idle down to 700 rpm or below and it should cure your problem. Let the engine idle for a minute or two before shutting off. Don't try to shut it off just as you come off plane, they will diesel like that every time.
 

Reinell-BRXL-191

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Re: 4.3 Cobra sputtering after key turned off

Dieseling is also caused by large amounts of carbon build-up in the combustion chamber - this carbon gets red hot during the combustion process and acts like a spark plug after the ignition is turned off, I would consider running some fuel additives like sea-foam or injector cleaners thru a few tanks of gas to try and clean up the tops of the pistons and heads - this could also cure your issue
 

Don S

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Re: 4.3 Cobra sputtering after key turned off

Marine engines (unlike automotive) seldom if ever buildup carbon like that. Basically because of the rpm and loads that marine engines run at.

It's not a real problem in automotive anymore either. With the fuels and the efi, they just burn a lot cleaner.

But the threat and the old tales do sell a lot of additives.
 

Reinell-BRXL-191

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Re: 4.3 Cobra sputtering after key turned off

Most carbon build up in older engines is caused by oil getting past the rings... in an engine of this age that has spent all of it's life at the top of the RPM scale, the probability that carbon is causing the issue of run over is significantly higher..

Also, as Idle said, if the timing is off enough to cause "flame over" after the ignition is shut off, could also be the cause.. but none the less, SOMETHING is causing the fuel to continue to ignite after the coil stops producing spark... fuel, efi, etc normally do not weigh in as said unless we are talking about modern computer controlled engines, which more than likely doesn't have much weight on an engine made between 1986 and 1993 - that is carburated, and most likely has points...

Carbon build up from overly rich main jets, leaking carb seals/blown power valve or failing rings is most likely the culprit. If nothing else, I would consider richening the idle a/f to try and cure the run over if the idle circuit is lean, it can cause this issue also...
 

pappysc2

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Jul 5, 2007
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Re: 4.3 Cobra sputtering after key turned off

Thanks for the responses. I will start working on it. I have a bottle of seafoam and am in the process of doing a carb kit. Will check timing as well and let you know how I progress.
 

Bondo

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Apr 17, 2002
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70,469
Re: 4.3 Cobra sputtering after key turned off

Thanks for the responses. I will start working on it. I have a bottle of seafoam and am in the process of doing a carb kit. Will check timing as well and let you know how I progress.

Ayuh,.... If ya have a Dieselin' incident, 'n the motor don't wanta Start after,...

Pull the spark plugs, cause it's Hydro-locked from turnin' backwards on it's last gasp...
 
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