When you turn your car off and it kind of stumbles for a second and then cuts off. Is that called dieseling? What causes it and does it hurt anything? I ask, because my car does it very rarely. I just drove my car after it sitting for more than a week, when I got back it sputtered, hood shook and then cut off.

 

my experience was if you shut it of over 100rpms then it would not happen try that and see if that works

 

Mime was doing this once, I think I changed the MAF relay and the burnoff relay, solved my problem.

 

Since, I don't have a CC car anymore does that change anything.

 

This happens because your engine is still getting air and fuel after it turns off, and you probably have a lot of carbon buildup in the combustion chambers that stays hot enough to ignite the mixture without spark plugs. It can also be caused by excessive heat from a lean condition. Make sure the throttle is not staying open after the ignition is cut, run some sort of cleaner through the engine..and if those don't work higher octane fuel will always help.

 

I've had pretty much the exact same situation. My car is has a carb and non-computer controlled ignition system.

What i have found this problem to be for me is too much initial timing advance.
There is an easy way i've found to make it not happen which consists of simply shutting off the car with it still in gear. Since there is a load on it, it wont run-on as before.

Try it, im sure it will work for ya

 

Not to step on any toes, but I think it better to solve the problem rather than the symptoms. Dieseling or Run-on is caused by the fuel in the combustion chamber being ignited by another means other than the spark plug. A high compression engine will have the same type of problem, because of the high air temps due to the higher air pressures. The more common reason is carbon buildup as was mentioned previously. The carbon will glow red hot and ignite the fuel, though not as well. The reason it is able to run on, on a carburated engine is because as long as there is air going through it, it feeds fuel. With fuel injection, the injectors stop their fuel feed unless they leak! To remove the carbon, get the engine good and hot. Take about 4 liters of clean water. Use distilled if you prefer, and pour this down the throttle body of the carb in a controlled fasion. At the same time operate the throttle by hand and make sure it doesn't stall! If it does(never happened to me) try and restart it. If it has hydraulicked the cylinders, then pull the plugs and crank the engine to remove and excess water. There shouldn't be very much. Before pulling the plugs try to pump some fuel in to give a better fuel ratio. The exhaust should be steaming, this is normal as the water is expanding in the combustion chamber, WHICH REMOVES THE CARBON! This process is also good for detonation prone engines. I t will not hurt any components. Water injection is used as an octane increaser as well, though there is much less being used.

Plugs will also cause run-on if theyare too 'hot' of a plug. Though this is also a rare occurance. Good Luck and don't worry about the water going through the engine, just keep the RPM at around 3000. It also may require more than 4 liters. Using other products may work, but water is free and works very well compared to a canned miracle product.

 

arthur has the right idea, but I would not suggest you "pour" water into your engine, fill an empty spray bottle full of water and mist it into the engine, this is an easy way to control the water going in, rev up the engine so it sucks it in and doesn't stall out the engine, if it the engine starts stumbling, just stop spraying water for a bit (common sense) there is absolutly no reason why you would hydrolock your engine doing this

 

Yep, mist the water in and watch all the black crap come out of the exhaust.

 

Thanks for the replies. Should I even bother, it only happens about once a month.

 

I would. If dieseling is being cause by carbon in the chambers, think about this:

The carbon can increase your susceptibility to detonation. You'll either have to increase the octane of the fuel you use, or put up with it. On newer cars, the knock sensor will save you from severe damage at the cost of power (from timing retard). On older cars, no such luck, and you're damaging your motor with every detonation.

We have a '79 vette that probably used regular (87) octane from the factory. When we bought it, it ran okay on 87 in the winter but knocked like mad unless you used 89 in the summer. It got slowly worse until it was knocking occasionally on premium (93) gasoline. Judicious use of top engine cleaner got it back to being able to run plus in the summer if the temperature didn't go over 90 degrees.

 

It is ironic that if you lean out your idle mixture, you detonate because of plain detonation, but if you richin it, you detonate because you build carbon in the crylinders.

I would rather clean out the engine, than detonate because of lean idle.