Cummins/Onan W3M-19 troubleshooting: 26 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan W3M-19 — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| Sticking valves | Return unit ¢o depot for repairs | |
| Broken valve spring | Replace | |
| Defective ignition wires | Replace | |
| Defective or improper magneto | Adjust or replace | |
| Low oil pressure | Oil too light; Oil badly diluted; Oil too low; Oil relief valve not eating | Inspect oil, Drain, refill with proper oil; Inspect oil, Drain, refill with proper oil; Add oil; Remove and clean oil relief valve |
| Engine stops unexpectedly | Repair or replace | |
| Engine backfires at carburetor | Lean fuel mixture; Fuel screen clogged; Air leaks at intake manifold; Poor fuel; Spark too late; Spark plug wires crossed; Intake valves leaking | Clean carburetor; Glean screen; Replace gaskets, tighten; Drain, fill with good, fresh fuel; Retime magneto; Install spark plug wires correctly; Return unit to depot for repairs |
| Excessive oil consumption, light blue smoky exhaust | Poor compression; Oil too light or diluted; Bearing clearance too great; Pressure registers low and this cannot otherwise be accounted for | Tighten head gasket and cylinder plugs. If still not corrected, return unit to depot for repairs; Drain, refill with correct oil; Return unit to depot for repairs; No remedy needed unless one of the next three remedies permanently corrects the trouble |
| High oil pressure | Oil too heavy; Clogged oil passage; Oil relief valve not eating | Inspect oil, Drain, refill with proper oil; No simple test, Return unit to depot for repairs; Remove and clean oil relief valve |
| Engine misses firing | Clean, adjust or replace spark plugs; Repair or replace magneto; No remedy needed if unit operated a great deal at light or no load | |
| Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load | Fuel mixture too rich; Carburetor float for leak and high level, needle valve for leak, jets for wear or damage, gasket washers for leaks; Choke not open | Adjust carburetor setting; Install needed carburetor parts, adjust float level; See that choke opens properly |
| Light pounding knock | Crankshaft bearing clearance too great; Low oil supply; Low oil pressure; Oil badly diluted | Return unit to depot for repairs unless one of the next three remedies permanently corrects the trouble; Add oil; Refer to symptom of low oil pressure for remedies; Change oil |
| Dull metallic thud, if not bad may disappear after few minutes operation. If bad, increases with load | Loose crankshaft bearing; If too bad, return to depot for repairs | Rewin unit to depot for repairs unless one of the next three remedies permanently corrects the trouble |
| Sharp metallic thud, especially when cold engine first started | Low oil supply; Low oil pressure; Oil badly diluted | Add oil; Refer to symptom of low oil pressure for remedies; Change oil |
| Pinging sound when engine is rapidly accelerated or heavily loaded | Carbon in cylinders; Spark too early; Wrong spark plugs; Spark plugs burned or carboned; Valves hot | Remove carbon from spark plug hole; Retime magneto, Install Champion 6M plugs, Install new plugs; Return to depot for repairs |
| Tapping sound | Tappet clearance too great; Broken valve spring (Engine mistiring) | Return to depot for repairs unless one of the next three remedies permanently corrects the trouble; Install new spring |
| Hollow clicking sound with cool engine under load | Loose pistons | Noise persists, indicates loose piston or piston rings. Otherwise return unit to depot for repairs; Indicates loose piston or piston rings needed. Otherwise return unit to depot for repairs |
| Engine cranks too stiffly | Too heavy oil in crankcase | Drain, refill with lighter oil. Try with hand crank, Return unit to depot for repairing |
| Engine will not start when cranked | Faulty ignition; Spark plugs; Magneto; Fuel tank empty; Carburetion, Carburetor adjustment; Shut-off cock; Fuel screen; Cylinders flooded; Poor fuel; Poor compression, Cylinder compression usually because of leaking valves; Wrong timing. Magneto timing | Clean, adjust or replace plugs; Repair or replace; Refill with good fuel; Tighten head gasket and spark plugs. If still not corrected return unit to depot for repairs |
| Engine runs but AC voltage does not build up | Exciter brushes and commutator, See that brushes seat well on commutator, are free in holders, are not worn shorter than 34” and have good spring tension. If commutator is rough or badly grooved, return unit to depot for repair; Poor commutation; Circuit, short No simple test, see paragraph 55. pairs.; Circuit or ground | Return unit to depot for repairing; Check for loose connections; Tighten connections, especially in exciter circuits; Check unusual conditions. Some fluctuating loads, such as a motor driving a reciprocating pump, are normal conditions. |
| Voltage is steady but engine not missing | Commutation or exciter commutator See that brushes seat well on commutator, are free in holders, are not worn shorter than 34” and have good spring tension. If commutator is rough or badly grooved, return unit to depot for repairing | Check for loose connections; Tighten connections especially in exciter circuits; Check unusual conditions. Some fluctuating loads, such as a motor driving a reciprocating pump, are normal conditions. |
| Generator overheating | Overloaded Ammeter: Reduce load. | |
| Voltage drops under heavy load | Engine lacks power. See symptom of engine missing under heavy load, Cylinder compression. Tighten head gasket and spark plugs, If still not corrected, return unit to depot for repairs See remedies for engine missing under heavy load.; Carburetor, Clean and adjust carburetor air cleaner; Choke. See that it opens wide enough; Carbon in cylinders. Remove carbon; Restricted exhaust line | |
| Engine misses at light load | Carburetor idle adjustment set wrong or clogged; Spark plug gaps too narrow; Intake air leak; Faulty ignition. Magneto Adjust or replace; Uneven compression, Cylinder compression Tighten head gasket and spark plugs If still not corrected return unit to depot for repairs | Adjust, clean if needed; Set at .030”; Tighten or replace gaskets; Adjust or replace Magneto; If still not corrected, return unit to depot for repairs |
| Engine misses at heavy load | Spark plugs Spark plugs Replace if defective; Faulty ignition. Magneto Adjust or replace; Clogged carburetor Clean; Clogged fuel screen Clean; Defective spark plug cables Replace | |
| Engine misses at all speeds | Fiouled spark plugs |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Oil too light; Oil badly diluted; Oil too low; Oil relief valve not eating. See the table for the matching fixes.
Documented causes: Lean fuel mixture; Fuel screen clogged; Air leaks at intake manifold; Poor fuel; Spark too late; Spark plug wires crossed; Intake valves leaking. See the table for the matching fixes.
Documented causes: Poor compression; Oil too light or diluted; Bearing clearance too great; Pressure registers low and this cannot otherwise be accounted for. See the table for the matching fixes.