"dieseling" out..

[skulley]

My car would kind of convulse and shiver and diesel out whenever I turned if off. It was really annoying and kind of embarrassing when pulling up in front of people. So I started using higher octane gas and it doesn't do it anymore! It is more expensive, but worth it I think to put in the better gas. I don't know if this is a problem for anyone else out there, but I thought it was worth posting.

[Petros]

A couple of things can cause this: a vacuum leak (making the mixture too lean), retarded timing (run it at 10 deg BTDC, not the factory 5 deg), or carbon build-up in the combustion chamber.

You can check for the last by removing a spark plug and look at the top of the piston when at top dead center (use a strong light helps). IF you have carbon build up you can clean it out using Gum Out, Seafoam or similar by filling each of the combustion chambers with it, let it sit overnight and than start it in the morning (with a lot of belching and coughing). It should loosen the carbon deposits and allow you blow it out the exhaust.]

Higher octane gas is not "Better", it is necessary with high compression motors to prevent ping or pre-ignition. IF you can run on regular without pre-ignition, than it cost less to operate the engine. High octane gas cost more to make so that is why it costs more. But I do not think the additives mixture or amount of impurities is any different.

Good luck.

[Neu]

Yeh, one of the common misconceptions about premium and regular is that premium can somehow net you better MPG, which it can.

I've literally had people tell me that it's because premium has more energy in it, it burns better and gives your car more power, no matter what engine it is.

Premium simply takes longer to ignite, so if you're pinging and knocking quite badly just use premium, or adjust your timing.

[simon84]

My car does this sometimes. Seems to happen when oil is getting low or the engine is running a bit hot (perhaps 'cuz the oil is low).
One time I threw it into 1st to kill it and the car lurched backwards. Is the engine somehow running backwards?

[Petros]

Yes, sometimes after the last deiesling 'chung' it will spin the engine backwards.

both premium and regular gasoline has 19,000 BTUs per pound, they have the same amount of energy, but sometimes depending on the engine design, the premium burns more efficiently, and you can get better mpg. But on most engines it does not make any difference.