Atlas Copco QAS 108 troubleshooting: 189 symptom-cause-remedy entries from the manufacturer's own service documentation.
Atlas Copco QAS 108 — full specs, parts & maintenance.
| Symptom | Cause | Remedy |
|---|---|---|
| Alternator does not excite | Blown fuse | Replace fuse |
| Alternator does not excite | Insufficient voltage | Increase speed by 15% |
| Alternator does not excite | No residual voltage | For an instant apply on the + and – terminals of the electronic regulator a 12 V battery voltage with a 30 ? resistor in series respecting the polarities |
| After being excited, alternator does not excite | Connections are interrupted | Check connection cables per drawings |
| Low voltage at no load | Voltage potentiometer out of setting | Reset voltage |
| Low voltage at no load | Intervention of protection | Check RPM |
| Low voltage at no load | Winding failure | Check windings |
| High voltage at no load | Voltage potentiometer out of setting | Reset voltage |
| High voltage at no load | Failed regulator | Substitute regulator |
| Lower than rated voltage at load | Voltage potentiometer out of setting | Reset voltage potentiometer |
| Lower than rated voltage at load | Intervention by protection | Current too high, power factor lower than 0.8, speed lower than 4% of rated speed |
| Lower than rated voltage at load | Failed regulator | Substitute regulator |
| Higher than rated voltage | Voltage potentiometer out of setting | Reset voltage |
| Higher than rated voltage | Failed regulator | Substitute regulator |
| Unstable voltage | Speed variation in engine | Check engine rotation |
| Unstable voltage | Regulator out of setting | Regulate the stability of regulator by acting on “STABILITY” potentiometer |
| Engine cranks but will not start | Incorrect starting procedure | Verify correct starting procedure |
| Engine cranks but will not start | No fuel | Check fuel in tank and manual shut-off valve |
| Engine cranks but will not start | Exhaust restricted | Check and correct exhaust restriction |
| Engine cranks but will not start | Fuel filter plugged or full of water | Replace fuel filter or drain water from filter |
| Engine cranks but will not start | Injection pump not getting air or fuel | Check fuel flow at supply pump or bleed fuel system |
| Engine cranks but will not start | Faulty injection pump or nozzles | Consult authorized diesel repair station |
| Engine hard to start or will not start | Improper starting procedure | Verify correct starting procedure |
| Engine hard to start or will not start | No fuel | Check fuel tank |
| Engine hard to start or will not start | Air in fuel line | Bleed fuel line |
| Engine hard to start or will not start | Cold weather | Use cold weather starting aids |
| Engine hard to start or will not start | Slow starter speed | See “Starter cranks slowly” |
| Engine hard to start or will not start | Crankcase oil too heavy | Use oil of proper viscosity |
| Engine hard to start or will not start | Improper type of fuel | Consult fuel supplier; use proper type of fuel for operating conditions |
| Engine hard to start or will not start | Water, dirt or air in fuel system | Drain, flush, fill, and bleed system |
| Engine hard to start or will not start | Clogged fuel filter | Replace filter element |
| Engine hard to start or will not start | Dirty or faulty injection nozzles | Consult authorized diesel repair station |
| Engine hard to start or will not start | Low engine oil level | Add oil to engine crankcase |
| Engine hard to start or will not start | Injection pump out of time | See your authorized servicing dealer or engine distributor |
| Engine hard to start or will not start | Low coolant temperature | Remove and check thermostat |
| Engine knocks | Engine overheating | See “Engine Overheats” |
| Engine knocks | Low coolant temperature | Remove and check thermostat |
| Engine knocks | Clogged fuel filter | Replace fuel filter element |
| Engine knocks | Water, dirt, or air in fuel system | Drain, flush, fill and bleed system |
| Engine knocks | Dirty or faulty injection nozzles | See your authorized servicing dealer or engine distributor |
| Engine runs irregularly or stalls frequently | Defective thermostat | Remove and check thermostat |
| Engine runs irregularly or stalls frequently | Defective temperature gauge or sender | Check gauge, sender and connections |
| Below normal engine temperature | Defective thermostat | Remove and check thermostat |
| Below normal engine temperature | Defective temperature gauge or sender | Check gauge, sender and connections |
| Lack of power | Engine overloaded | Reduce load |
| Lack of power | Intake air restriction | Service air cleaner |
| Lack of power | Clogged fuel filter | Replace filter elements |
| Lack of power | Improper type of fuel | Use proper fuel |
| Lack of power | Overheated engine | See “Engine Overheats” |
| Lack of power | Below normal engine temperature | Remove and check thermostat |
| Lack of power | Improper valve clearance | See your authorized servicing dealer or engine distributor |
| Lack of power | Dirty or faulty injection nozzles | See your authorized servicing dealer or engine distributor |
| Lack of power | Injection pump out of time | See your authorized servicing dealer or engine distributor |
| Lack of power | Turbocharger not functioning | See your authorized servicing dealer or engine distributor |
| Lack of power | Leaking exhaust manifold gasket | See your authorized servicing dealer or engine distributor |
| Lack of power | Defective aneroid control line | See your authorized servicing dealer or engine distributor |
| Lack of power | Restricted fuel hose | Clean or replace hose |
| Lack of power | Low fast idle | See your authorized servicing dealer or engine distributor |
| Low oil pressure | Low oil level | Add oil |
| Low oil pressure | Improper type of oil | Drain, fill crankcase with proper viscosity and quality |
| Low oil pressure | Crankcase oil too light | Use proper viscosity oil |
| Low oil pressure | Oil leaks | Check for leaks in lines, gaskets, and drain plug |
| Low oil pressure | Restricted crankcase vent tube | Clean vent tube |
| High oil consumption | Defective turbocharger | See your authorized servicing dealer or engine distributor |
| High oil consumption | Improper type of fuel | Use proper fuel |
| High oil consumption | Low engine temperature | Warm up engine to normal operating temperature |
| High oil consumption | Defective thermostat | Remove and check thermostat |
| High oil consumption | Defective injection nozzles | See your authorized servicing dealer or engine distributor |
| Engine emits white smoke | Engine out of time | See your authorized servicing dealer or engine distributor |
| Engine emits white smoke | Improper type of fuel | Use proper fuel |
| Engine emits white smoke | Clogged or dirty air cleaner | Service air cleaner |
| Engine emits white smoke | Engine overloaded | Reduce load |
| Engine emits white smoke | Injection nozzles dirty | See your authorized servicing dealer or engine distributor |
| Engine emits black or gray exhaust smoke | Turbocharger not functioning | See your authorized servicing dealer or engine distributor |
| Engine emits black or gray exhaust smoke | Engine overloaded | Reduce load |
| Engine overheats | Low coolant level | Fill radiator to proper level, check radiator and hoses for loose connections or leaks |
| Engine overheats | Faulty radiator cap | Have service company check |
| Engine overheats | Stretched poly-vee belt or defective belt tension | Check automatic belt tensioners and check belts for stretching. Replace as required |
| Engine overheats | Low engine oil level | Check oil level. Add as required |
| Engine overheats | Cooling system needs flushing | Flush cooling system |
| Engine overheats | Defective thermostat | Remove and check thermostat |
| Engine overheats | Defective temperature gauge or sender | Check water temperature with thermometer and replace, if necessary |
| Engine overheats | Incorrect grade of fuel | Use correct grade of fuel |
| High fuel consumption | Improper type of fuel | Use proper type of fuel |
| High fuel consumption | Clogged or dirty air cleaner | Service air cleaner |
| High fuel consumption | Engine overloaded | Reduce load |
| High fuel consumption | Improper valve clearance | See your authorized servicing dealer or engine distributor |
| High fuel consumption | Injection nozzles dirty | See your authorized servicing dealer or engine distributor |
| High fuel consumption | Engine out of time | See your authorized servicing dealer or engine distributor |
| High fuel consumption | Defective turbocharger | See your authorized servicing dealer or engine distributor |
| High fuel consumption | Low engine temperature | Check thermostat |
| Engine shuts down after approx. 15 seconds | Poor connection on oil or coolant temperature switches | Check connections |
| Engine shuts down after approx. 15 seconds | DIP switch on controller in wrong position | Check controller DIP switches |
| Undercharged system | Excessive electrical load from added accessories | Remove accessories or install higher output alternator |
| Undercharged system | Excessive engine idling | Increase load or shut off engine |
| Undercharged system | Poor electrical connections on battery, ground strap, starter, or alternator | Inspect and clean as necessary |
| Undercharged system | Defective battery | Test battery |
| Undercharged system | Defective engine alternator | Test charging system |
| Battery uses too much water | Cracked battery case | Check for moisture and replace as necessary |
| Battery uses too much water | Defective battery | Test battery |
| Battery uses too much water | Battery charging rates too high | Test charging system |
| Battery uses too much water | Loose or corroded connections | Clean and tighten connections |
| The starter motor turns the engine too slowly | Battery capacity too low | |
| The starter motor turns the engine too slowly | Bad electrical connection | |
| The starter motor turns the engine too slowly | Fault in starter motor | |
| The starter motor turns the engine too slowly | Wrong grade of lubricating oil | |
| The engine does not start or is difficult to start | Starter motor turns engine too slowly | |
| The engine does not start or is difficult to start | Fuel tank empty | |
| The engine does not start or is difficult to start | Fault in fuel control solenoid | |
| The engine does not start or is difficult to start | Restriction in a fuel pipe | |
| The engine does not start or is difficult to start | Fault in fuel lift pump | |
| The engine does not start or is difficult to start | Dirty fuel filter element | |
| The engine does not start or is difficult to start | Air in fuel system | |
| The engine does not start or is difficult to start | Fault in atomisers | |
| The engine does not start or is difficult to start | Cold start system used incorrectly | |
| The engine does not start or is difficult to start | Fault in cold start system | |
| The engine does not start or is difficult to start | Restriction in fuel tank vent | |
| The engine does not start or is difficult to start | Wrong type or grade of fuel used | |
| The engine does not start or is difficult to start | Restriction in exhaust pipe | |
| Not enough power | Restriction in a fuel pipe | |
| Not enough power | Fault in fuel lift pump | |
| Not enough power | Dirty fuel filter element | |
| Not enough power | Restriction in air filter/cleaner or induction system | |
| Not enough power | Air in fuel system | |
| Not enough power | Fault in atomisers or atomisers of an incorrect type | |
| Not enough power | Restriction in fuel tank vent | |
| Not enough power | Wrong type or grade of fuel used | |
| Not enough power | Restricted movement of engine speed control | |
| Not enough power | Restriction in exhaust pipe | |
| Not enough power | Engine temperature is too high | |
| Not enough power | Engine temperature is too low | |
| Alternator does not excite | Insufficient residual voltage | Increase the speed by 15 % |
| After being excited alternator does not excite | No residual voltage | For an Instant apply on the + and – terminals of the electronic regulator a 12 V battery voltage with a 30 Ω resistor in series respecting the polarities |
| After being excited alternator does not excite | Connections are interrupted | Check connection cables as per attached drawings |
| Lower than rated voltage at load | Rotating bridge failure | Check diodes, disconnect cables |
| Higher than rated voltage at load | Voltage potentiometer out of setting | Reset voltage potentiometer |
| Higher than rated voltage at load | Failed regulator | Substitute regulator |
| Misfire | Restriction in a fuel pipe | |
| Misfire | Fault in fuel lift pump | |
| Misfire | Dirty fuel filter element | |
| Misfire | Air in fuel system | |
| Misfire | Fault in atomisers or atomisers of an incorrect type | |
| Misfire | Fault in cold start system | |
| Misfire | Engine temperature is too high | |
| Misfire | Incorrect valve tip clearances | |
| The pressure of the lubricating oil is too low | Wrong grade of lubricating oil | |
| The pressure of the lubricating oil is too low | Not enough lubricating oil in sump | |
| The pressure of the lubricating oil is too low | Defective gauge | |
| The pressure of the lubricating oil is too low | Dirty lubricating oil filter element | |
| High fuel consumption | Restriction in air filter/cleaner or induction system | |
| Unstable voltage | Blown fuse | Replace fuse |
| Unstable voltage | Insufficient residual voltage | Increase the speed by 15 % |
| Unstable voltage | No residual voltage | For an Instant apply on the + and – terminals of the electronic regulator a 12 V battery voltage with a 30 Ω resistor in series respecting the polarities |
| Unstable voltage | Connections are interrupted | Check connection cables as per attached drawings |
| Unstable voltage | Voltage potentiometer out of setting | Reset voltage |
| Unstable voltage | Intervention of protection | Check rpm |
| Unstable voltage | Winding failure | Check windings |
| Unstable voltage | Failed regulator | Substitute regulator |
| Unstable voltage | Intervention by protection | Current too high, power factor lower than 0.8; speed lower than 4% of rated speed |
| Unstable voltage | Rotating bridge failure | Check diodes, disconnect cables |
| High fuel consumption | Fault in atomisers or atomisers of an incorrect type | |
| High fuel consumption | Fault in cold start system | |
| High fuel consumption | Wrong type or grade of fuel used | |
| High fuel consumption | Restricted movement of engine speed control | |
| High fuel consumption | Restriction in exhaust pipe | |
| High fuel consumption | Engine temperature is too low | |
| High fuel consumption | Incorrect valve tip clearances | |
| Black exhaust smoke | Restriction in air filter/cleaner or induction system | |
| Black exhaust smoke | Fault in atomisers or atomisers of an incorrect type | |
| Black exhaust smoke | Fault in cold start system | |
| Black exhaust smoke | Wrong type or grade of fuel used | |
| Black exhaust smoke | Restriction in exhaust pipe | |
| Black exhaust smoke | Engine temperature is too low | |
| Black exhaust smoke | Incorrect valve tip clearances | |
| Black exhaust smoke | Engine overload | |
| Blue or white exhaust smoke | Wrong grade of lubricating oil | |
| Blue or white exhaust smoke | Fault in cold start system | |
| Blue or white exhaust smoke | Engine temperature is too low | |
| The engine knocks | Fault in fuel lift pump | |
| The engine knocks | Fault in atomisers or atomisers of an incorrect type | |
| The engine knocks | Fault in cold start system | |
| The engine knocks | Wrong type or grade of fuel used | |
| The engine knocks | Engine temperature is too high | |
| The engine knocks | Incorrect valve tip clearances | |
| The engine runs erratically | Fault in fuel control | |
| The engine runs erratically | Restriction in a fuel pipe | |
| The engine runs erratically | Fault in fuel lift pump | |
| The engine runs erratically | Dirty fuel filter element | |
| The engine runs erratically | Restriction in air filter/cleaner or induction system |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Improper type of fuel; Clogged or dirty air cleaner; Engine overloaded; Improper valve clearance. See the table for the matching fixes.
Documented causes: Engine overloaded; Intake air restriction; Clogged fuel filter; Improper type of fuel. See the table for the matching fixes.
Documented causes: Improper starting procedure; No fuel; Air in fuel line; Cold weather. See the table for the matching fixes.