Short answer up front: Hino FG17 / FG19 trucks do NOT use a carburetor — they use a diesel fuel injection system (mechanical or electronically‑controlled injection pump plus injectors). Below is a workshop‑style, beginner‑mechanic guide that explains every component of the diesel fuel system, the theory of how it works, common failures, and step‑by‑step workshop procedures to diagnose, service, and repair it. Follow factory torque/timing specs for your exact engine and use proper safety procedures.

1) What you actually have (overview)
- Diesel fuel system = fuel tank → pickup → primary filter / water separator → lift (transfer) pump → secondary filter → injection pump → high‑pressure lines → injectors. Return/overflow lines carry excess back to tank.
- Key components (what they are and what they do):
- Fuel tank & pickup: stores diesel; pickup draws fuel to the pump.
- Primary filter / water separator: first stage; removes large particles and separates water. Many have a drain/bowl.
- Lift (transfer) pump: moves fuel from tank to injection pump; can be mechanical (gear/diaphragm) or electric. Analogy: a bicycle pump that feeds the main pump.
- Secondary (fine) filter: removes fine particles and prevents contamination of the injection pump and injectors.
- Injection pump (mechanical or electronic): meters and times high‑pressure doses of fuel to each cylinder. Internals: cam rotor or camshaft, plungers and barrels, delivery valves, governor (regulates RPM/load), advance mechanism for timing, throttle/rack.
- High‑pressure lines: carry fuel under very high pressure from pump to injector. Analogy: garden hose vs. needle — these are the needle lines.
- Injectors: atomize fuel into the combustion chamber; components: nozzle tip, needle, spring, body, sealing washer. They open at a specific pressure to spray a fine cone.
- Return/overflow lines: carry excess/backflow back to tank.
- Cold‑start devices / heaters (if fitted): help start in cold weather.

2) Theory — how it works (simple)
- Diesel engines compress only air, making it hot. The injection pump times and meters very small, precisely measured shots of fuel into the hot compressed air. The atomized fuel mixes and ignites by compression alone — no spark or carburetor needed.
- The injection pump’s cam and plungers determine how much fuel is pushed and when. The governor adjusts fuel amount to maintain speed/load. Injectors atomize at a set opening pressure to produce correct spray pattern.
- Timing matters: injecting too early or too late causes rough running, smoke, loss of power. Metering matters: too much fuel → black smoke; too little → poor power/white smoke or misfire.

3) Symptoms that indicate fuel‑system repair is needed
- Hard starting or long cranking
- Excessive smoke: black (overfuel), white (unburnt fuel/water, cold), blue (oil)
- Loss of power, poor acceleration, engine knocks
- Rough idle or misfiring
- Sudden no‑start after running out of fuel or filter change (air in system)
- Visible fuel leaks or water in separator

4) Safety & tools
- Safety: diesel is flammable; work in ventilated area; wear eye protection and gloves; have a fire extinguisher; avoid skin contact with high‑pressure spray (it can inject fluid into skin — seek immediate medical help if that happens).
- Tools: basic hand tools, torque wrench, injector puller, fuel filter wrench, clean rags, container for fuel, screwdriver, feeler gauges, dial gauge / degree wheel (for timing), fuel pressure gauge (supply/bleed), vacuum hand pump / priming pump, injector bench tester or shop service for injectors/pump, timing lock/wooden dowels per manual.
- Special equipment usually needed for full overhaul: pump test bench, injector flow/pressure tester — send pump/injectors to specialist if you don’t have these.

5) Workshop procedures — step‑by‑step (practical guide for common repairs and diagnosis)
A. Preparation and safety
- Park on level, set park brake, block wheels. Disconnect battery negative if you will be removing electrical components or working extensively.
- Clean around fuel parts before opening lines to prevent dirt ingress.

B. Visual inspections & quick checks
- Check for leaks, damaged hoses, blocked breather, condition of fuel filters, water in drain bowl.
- Drain water separator: open drain cup, drain water and sediment until clear diesel flows.
- Verify lift pump operation: in ignition ON (not start) you may hear electric lift pump; mechanical pump should pump while cranking. If no fuel flow to pump, suspect pickup/filter or tank issue.

C. Replace filters & prime
- Replace primary (water separator) and secondary filters with new elements. Always prefill filters with clean diesel if possible.
- Bleed/prime: Many systems have a manual primer pump or a bleed screw on the injection pump. Procedure:
1. Open the bleeder screw at the pump or on the filter housing.
2. Operate manual primer or crank engine a few seconds (do not over‑crank) until steady fuel without air bubbles flows from the bleeder.
3. Close bleeder, then crank to start.
- If engine won't start, re‑bleed; air trapped in the system is the most common no‑start cause after filter change.

D. Checking supply pressure / lift pump
- Fit supply pressure gauge between tank/filter inlet and the pump to check lift pump output. Compare to spec in workshop manual (typical numbers vary; consult manual).
- If low or no supply pressure: clean/replace pickup strainer, check tank, replace lift pump.

E. Injector checks
- Remove injectors one at a time (mark location). Keep ports covered to prevent debris in cylinders.
- Visual check: carbon, deposits, damaged tips or needle sticking.
- Test spray pattern and opening pressure: on injector tester/bench, check that opening pressure and spray cone match spec. Weak spray = poor atomization → incomplete combustion and black smoke. Replace or recondition injectors that fail.
- Replace injector copper washer/seal whenever removing the injector.

F. Injection pump checks and timing
- Before removing pump: mark pump body position relative to engine block and mark degree/clock positions of engine flywheel (TDC) and pump rotor (if visible). These marks are vital to restore timing.
- To check timing: bring #1 cylinder to TDC on compression stroke. Align engine timing mark. Rotate pump to align its timing mark with engine’s index. Use service manual method (dial indicator or timing pin) to confirm.
- If adjustment needed: loosen pump mounting bolts slightly, rotate pump body forward or backward to advance/retard timing per spec, then retighten bolts and recheck.
- Note: Some pumps have a timing pin / locking tool; others have clocking marks. Always use factory procedure.

G. Governor and control checks
- Inspect governor and throttle linkage for binding, corrosion, or broken springs. Clean and lubricate pivot points. Check for correct throttle travel and idle stop adjustments per manual.

H. Overhaul / rebuild
- Injection pump overhaul (plungers/barrels/delivery valves/governor) requires a pump test bench for calibration. Unless you have the bench and training, remove the pump and send to an authorized rebuilder or supplier. Overhaul steps (overview):
- Disassemble, clean, measure wear (plunger, barrel, cam lobes), replace seals/o‑rings, replace worn delivery valves, reassemble and calibrate on bench to restore correct timing and fuel delivery per cylinder.
- Injectors can be serviced or replaced; rebuilding injectors is common at a specialist shop.

I. Reassembly, leak check, test run
- Tighten lines to correct torque; replace crush washers on high‑pressure connections where required.
- Prime system fully, ensure no air remains.
- Start engine and run at idle; watch for leaks, listen for odd noises, check smoke, and monitor oil pressure and temperature.
- Road test under load: check responsiveness and smoke behavior. Recheck timing and leak points after a short run.

6) What can go wrong — specific failure modes and fixes
- Air in system after filter change: no start / long crank → bleed fully.
- Water in fuel: corrosion, poor combustion, rusted parts → drain separator, replace filters, treat tank, replace contaminated fuel.
- Clogged filters: reduced power and poor throttle response → replace filters, check supply lines.
- Worn injector nozzle / poor spray: black smoke, rough running → replace or rebore injectors.
- Leaking injector body seals: smoking and low compression → replace copper washers, torque to spec.
- Worn pump plungers / barrels: loss of power on one or more cylinders, uneven running → pump overhaul.
- Wrong timing: knocking, loss of power, excessive smoke → adjust pump timing.
- Damaged high‑pressure lines or loose fittings: fuel leaks (fire hazard) → replace lines and tighten fittings to spec.
- Sticking governor or throttle linkage: surging / over‑run → clean/adjust.
- Contaminated fuel (suspended particles, microbes): filters plug quickly → clean tank, drain, use antimicrobial additives if necessary.

7) Useful diagnostic checklist (quick)
- Fuel in tank? (common, obvious)
- Fuel filter condition and water drained?
- Lift pump working and supply pressure OK?
- Air bled from system?
- Injector spray pattern OK?
- Injection pump timing correct?
- Any visible leaks?

8) Practical tips and analogies (to make it simple)
- Think of the whole fuel system as the circulatory system: tank = reservoir, lift pump = heart pump sending fuel to the brain (injection pump), the injection pump is the control center that decides how much blood (fuel) each arm/leg (cylinder) gets at a precise beat (timing), injectors are the capillaries that distribute it.
- If a filter clogs it’s like an artery narrowing — downstream parts starve and perform poorly.
- When bleeding, imagine removing air bubbles from a soda straw; until air is out, you won’t get fluid consistently.

9) When to call a specialist
- If injection pump needs internal repairs, or injectors fail bench tests, send them to a qualified pump/injector rebuilder with the correct calibrated test bench.
- Any time precise timing and pump calibration are required beyond simple index marks, rely on skilled technicians.

10) Final notes
- Always consult the Hino factory workshop manual for your exact engine model for bolt torques, timing degrees, and pressure specs before making permanent adjustments.
- Regular maintenance: change primary and secondary filters on schedule, drain water separator regularly, keep tank clean and topped up to avoid condensation, and inspect lines for leaks.

This guide gives you the system layout, component functions, why problems happen, and step‑by‑step workshop actions for diagnosis and common repairs. For pump or injector reconditioning you’ll likely need a specialist with a test bench.
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From the Archives: Hino FG Series Old footage of the Hino FG Series truck.

From the Archives: Hino FG Series Old footage of the Hino FG Series truck.

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