Engine runs out of oil in less than one week, and engine raggs.

Sounds like that car is the proverbial POS. Did you check for spark? - need a strong one with a car burning that much oil and the plugs getting fouled like that. Need to replace those rings!

the only way you lose oil is by burning it or leaking it, if your car blows a lot of blue smoke, then you are burning it {engine rebuild or replace} if there is oil on the ground when you park, then you need to determine where the leak is coming from, pressure wash underneath before taking it to a mechanic, we hate getting under dripping dirty cars. glad to help.

Knock at low rpm and high rpm" It may be oil pump , After oil heats up it gets thinner and and less lubracated. I would change the oil and add some oil stabalizer, shouls help, if not probaly a rod.

My guess would be a leaking intake or head gasket. Water in the cylinder(s) is shorting the spark plug until the temp comes up on the engine. The white smoke is the coolant being burnt off. check your coolant level it may be low.

Go to Advance Auto or Autozone and tell them you need a free OBD2 scan.

Change your engine oil with 10W30 every 4,000kms. Change your transmission oil with Honda MTF every 6 months. Change your Differential Oil with 75W90 every 6 months. Check the tire pressure every month. Treat the top with a quality vinyl top protectant often (I use Ragg Topp brand). Wash & wax painted surfaces often. Treat the leather interior with UV protectant designed for convertible top cars (I use Wolfgang brand).

That's all I can think of!

the light was tripped by the low oil your problem was truly minor

Diesels do lose a little oil out the blow-by tube. If the engine temp. is higher then normal then you will lose more then normal amounts. If you are not leaking it then you are burning it, Possibly worn rings, head-gasket, or oil leak inside turbo. 68 MPH and higher doesn't sound unusual, is the engine still stock?

THIS SOUNDS LIKE A INTAKE MANIFOLD VACUUM LEAK. TO CHECK THIS GET A CAN OF CAR SPRAY AND SRAY AROUND THE INTAKE GASKET WHILE THE ENGINE IS RUNNING, IF THE ENGINE HAS A LEAK IT WILL START RUNNING OK WHILE THE YOU ARE SPRAYING.

oil pressure switch faulty