1)The compression is possibly low as Alain suggested. Have the valves adjusted properly first before doing anything else.
2) First check the vacuum hoses, especially the one to the shut-off valve. If all hoses are good and connected, remove the hose to the shut-off valve and connect the valve to a hand vacuum pump while the engine is running. Apply vacuum. If the engine shuts off, the shut-off valve is good. The last thing is the key switch which may not channel vacuum to the shutoff valve. It can be checked by a vacuum gauge. It may be just a disconnected hose at the switch. I assume that the engine vacuum pump is in good workig order.
3)One quart in 20 miles? I have no idea what is going on. Smoke coming out of an oil filler hole of a diesel engine is not necessary bad. My suggestion is to do a compression test.
[This message has been edited by be459 (edited 06-16-2000).]