Diesel cars with dead battery and alternator.

[ericnguyen]

Dear friends:

Since diesel engines do not use spark plugs, I wonder whether it's true that a diesel car (e.g. an old one without any computer-controlled emission/timing etc..., and no lights) would continue to run until it is out of fuel even if its battery and alternator are completely dead.

If it is, it's a great advantage of a diesel car hehe.

Eric

and it certainly is an advantage in daylight for machines like my father's old 1967 Minneapolis-Moline 670 farm tractor, but I'd hate to be on the same road with someone without working brake lights and turn signals even in daytime.

[banflu]

not only that, probably it would be unstoppable!

i dont know about Merc diesels, but some diesels use a small solenoid in the diesel injection pump to stop the diesel flow when you put the key to "STOP". thus, if there is no 12v supply from a battery, there wont be a 12V supply on this solenoid when you try to stop the engine. so it will go on forever (or until you manually close the fuel flow).

if the solenoid is the other way round, i.e. 12V to open, 0v to close, the engine will stop if you disconnect the battery and alternator.

the shut-down valve is controlled by vacuum from an accessory pump (and thus minor vacuum leaks can cause the sort of "unstoppablility" you describe -- if you don't know about the lever labeled "STOP" under the hood -- there are a lot of threads on this site which begin with a panicy post from someone who can't shut his car off) rather than by electricity, like VWs, etc. Some of the really old ones had cable or linkage operated shut-offs, like on the Bosch injection pumps on a lot of farm tractors.

[pentoman]

I remember reading, when MB first came out with its 'Common Rail' Diesel engines that they had a test day in -insert exotic car launch location here- for journalists. For some reason, a lot of the cars had problems and they couldn't switch them off..! Automatics meant you couldn't even stall it...

'thorough' engineering, Mercedes late '90s style.