Brief safety first: diesel is flammable and under pressure. Work in ventilated area, wear eye protection, keep fire source away. Keep rags and a catch container for spilled fuel. Minimal talk — steps with theory and how each step fixes the fault.

Goal: remove air from the low‑pressure fuel side and high‑pressure feed so the injection pump and injectors see continuous, incompressible fuel. Air in the lines compresses, reduces or interrupts fuel delivery, causes hard starting, stumbling, misfire, loss of power.

Overview of the systems (theory, short):
- Low‑pressure side: tank → lift (electric) pump → fuel filter/water trap with primer/bleed screw → inlet to injection pump. This side must be full of fuel and free of air.
- High‑pressure side: injection pump → high‑pressure lines → injectors. Any air trapped here prevents correct injection timing/quantity because air is compressible.
- Bleeding/priming evacuates air and re‑establishes an unbroken column of liquid fuel so the injection pump can build correct pressure and deliver correct volume at the right time.

Ordered procedure (apply to 1HZ / 1PZ / 1HD‑T; small location differences only):

1) Identify the components and any obvious leaks
- Locate lift pump, fuel filter/water trap (filter head) and its bleed screw/primer, the injection pump and the high‑pressure lines/injectors.
- Theory / how this fixes: finding a leak identifies the air ingress point. If you just bleed but don’t stop the leak, air will be reintroduced and the fault returns.

2) Fix visible leaks first (if present)
- Tighten loose fittings, replace perished rubber hoses, replace O‑rings/banjo washers on pump/injector joints or replace cracked hard lines.
- Theory / how this fixes: air enters through imperfect seals. Replacing seals or damaged lines removes the source of air ingress so a successful bleed remains effective.

3) Bleed the fuel filter / use the hand primer
- On the filter head: open the bleed screw (small screw/valve usually near filter) and operate the hand primer (if fitted) repeatedly until clean fuel (no bubbles) flows from the bleed outlet, then close the screw. If there is no hand primer, use the electric lift pump to push fuel while the bleed screw is open.
- Theory / how this fixes: the filter head is the first high point where air can collect. Opening the bleed and forcing fuel through displaces trapped air. Closing the bleed when only fuel flows seals the low‑pressure side full of liquid.

4) Prime the injection pump inlet if required
- If the pump inlet remains starved, loosen the inlet connection to the injection pump (or a banjo/union before the pump) until fuel flows bubble‑free then tighten.
- Theory / how this fixes: any air pocket between filter and pump must be expelled. Directly venting at the pump inlet ensures the pump receives only fuel, allowing it to pressurize and meter correctly.

5) Bleed the high‑pressure side if necessary (if engine still refuses or runs poorly)
- For mechanical pumps you can loosen the union/nut on the high‑pressure feed at the pump or at the first injector line, then crank the engine slowly or operate the lift pump until fuel, free of air, comes out. Tighten that union when only fuel appears. Repeat for each high‑pressure line if air has migrated up the lines.
- Alternative: some technicians loosen each injector line at the injector slightly and crank until fuel appears, working injector by injector.
- Theory / how this fixes: air trapped in high‑pressure lines compresses under pump pressure and prevents correct metering/injection. Venting each line removes compressible air so the pump delivers a precise liquid column to each injector.

6) Crank/run in stages
- After bleeding/priming and tightening, crank the engine until it starts. If it starts but runs roughly, cycle the primer and repeat bleeding points where bubbles reappear. Once it runs, keep it at idle for a short time and monitor for fuel leaks or air ingress.
- Theory / how this fixes: cranking and running moves fuel through the whole system repeatedly; if any air pockets remain they will show up (bubbles) at the bleed points so you can evacuate them.

7) Final checks and secure everything
- Tighten all fittings to the correct torque (don’t overtighten soft fittings), replace any washers used, re‑mount filter elements, dispose of spilled fuel safely.
- Theory / how this fixes: mechanical security prevents reintroduction of air. Correct torque prevents leaks without damaging fittings.

Why these steps solve the symptom (concise):
- Air is compressible; fuel is not. The injection pump and injectors require an incompressible column of fuel to build pressure and deliver a timed, metered shot. Bleeding removes the compressible air, and repairing/replacing leaking components stops new air entering. Once the system is full of fuel and sealed, pump pressure, timing and injection quantity return to normal and the engine starts/runs smoothly.

Quick troubleshooting cues (short):
- If bleeding never gives steady fuel: likely a fuel supply fault (lift pump dead, clogged filter, collapsed hose sucking in air) — repair/replace.
- If bleeding works but air reappears after a short run: there’s a leak or a failing lift pump drawing air.
- If engine runs but misfires on one cylinder: check that cylinder’s high‑pressure line and injector sealing washers.

End.
rteeqp73

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Toyota Landcruiser HDJ81 big end bearings issue. 1HD-T engine. Checked big end bearings due to customers concerns with an old bearing problem that was an issue year's ago with Toyota.

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