Brief theory
- "Blow-by" = combustion gases that bypass piston rings into the crankcase. They carry pressure, water, unburnt fuel and oil vapor.
- The blow-by tube/breather (PCV) system routes those gases out of the crankcase and back into the intake (or into a catch can) so they are re‑burned instead of pressurizing and oil‑fouling the engine bay.
- On the Nissan YD22DDTi the common parts: rocker‑cover breather outlet, flexible breather hose/tube, one‑way valve (if fitted), and connection into the turbo/air intake. Failures: splits/collapses, clogged sludge, or failed valve cause high crankcase pressure, oil leaks, oil drawn into intake/turbo, oil smoke and turbo seals damage.

Ordered diagnostic + repair (concise, with theory at each step)

1) Safety & prep
- Cool engine, park level, battery negative disconnected if you’ll work near electrics.
- Theory: no live work on a hot engine; depressurizing avoids burns and unplanned ingestion of oil/fumes.

2) Access and visual inspection
- Remove plastic engine covers and intake ducting to expose rocker cover breather and hose.
- Visually inspect hose, elbows, clamps and valve for cracks, hardening, oil sludge or collapse.
- Theory: visual failures commonly show as external cracks or sludge which block flow.

3) Functional check
- With hose disconnected at intake, crank engine briefly (or run at idle) and feel for steady flow (suction into intake or pressure out of crankcase depending on layout). Smell oil, observe heavy mist.
- If available, do a simple crankcase pressure test (install a gauge at breather port); excessive positive pressure indicates ring/PC problems, but an obstructed tube will aggravate pressure.
- Theory: blocked/failed breather prevents evacuation of blow‑by → pressure builds and forces oil out seals.

4) Remove the breather tube assembly
- Loosen clamps, remove retaining clips and pull tube from rocker cover and intake/turbo inlet. Inspect mating O‑rings/seals.
- Theory: direct inspection of internal bore and valve shows sludge, tears or collapsed tubing.

5) Clean and inspect parts
- If reusable, clean internal sludge with solvent, blow through with compressed air, check one‑way valve operation by hand. Replace any brittle or oily saturated flexible hose.
- Theory: sludge builds and restricts flow; cleaning restores diameter but degraded rubber must be replaced.

6) Replace faulty components
- Fit a new OEM or high‑quality replacement breather hose, new clamps and any one‑way valve or grommets as required. Replace O‑rings/seals on connections.
- Theory: new hose restores full open flow path, elastic seals restore airtight connection, valve (if present) restores correct flow direction and prevents backflow under boost.

7) Reinstall and secure
- Reconnect tube to rocker cover and intake/turbo elbow, tighten clamps to firm snug (do not over‑torque plastic fittings). Refit intake ducting and covers.
- Theory: secure joints prevent leaks and maintain designed vacuum/pressure routing.

8) Start and verify
- Start engine, check for oil leaks around joints, run to steady idle and recheck crankcase flow at breather. Confirm reduced crankcase pressure on gauge if used. Check for reduced smoke and no oil collecting in turbo/airbox.
- Theory: restored ventilation evacuates blow‑by into intake for re‑combustion or catch‑can, normalizing crankcase pressure and stopping external oil leaks and oil ingestion.

How the repair fixes the fault (concise)
- Replacing/cleaning the tube removes physical restriction and restores an open path for blow‑by gases. That lowers crankcase pressure so seals and gaskets no longer weep oil.
- Replacing failed valves prevents boost from over‑pressurizing the crankcase and prevents contaminated air/oil being drawn into the intake/turbo.
- Restored flow reduces oil carry‑over, decreases smoke, prevents turbo seal wear and reduces oil deposits in the intake, improving engine longevity and performance.

Common practical notes (brief)
- Replace rubber hose and grommets rather than reusing brittle parts.
- If crankcase pressure remains high after fixing the tube, investigate ring/cylinder wear or turbo re‑circulation faults.
- Use OEM or quality aftermarket parts for resistance to oil/heat.

Done.
rteeqp73

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