Cummins/Onan W3M-19 troubleshooting: 98 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 |
|---|---|---|
| Engine cranks too stiffly | Too heavy oil in crankcase | Drain, refill with lighter oil |
| Engine cranks too stiffly | Engine stuck | Try with hand crank. Return unit to depot for repairing |
| Engine will not start when cranked | Faulty ignition (spark plugs) | Clean, adjust or replace plugs |
| Engine will not start when cranked | Faulty ignition (magneto) | Repair, or replace |
| Engine will not start when cranked | Lack of fuel or faulty carburetion — fuel tank empty | Refill |
| Engine will not start when cranked | Lack of fuel or faulty carburetion — carburetor adjustment | Adjust |
| Engine will not start when cranked | Lack of fuel or faulty carburetion — shut-off cock | Open |
| Engine will not start when cranked | Lack of fuel or faulty carburetion — fuel screen | Clean |
| Engine will not start when cranked | Cylinders flooded | Crank few times with spark plugs removed |
| Engine will not start when cranked | Poor fuel | Drain, refill with good fuel |
| Engine will not start when cranked | Poor compression, usually because of leaking valves | Tighten head gasket and spark plugs. If still not corrected return unit to depot for repairs |
| Engine will not start when cranked | Wrong timing (magneto timing) | Tighten head gasket and spark plugs. If still not corrected return unit to depot for repairs |
| Engine runs but A.C. 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 3/4" and have good spring tension. If commutator is rough or badly grooved, return unit to depot for repair |
| Engine runs but A.C. voltage does not build up | Poor commutation, open circuit, short circuit or ground in generator | No simple test, see paragraph 55. Return unit to depot for repairs |
| Engine runs but A.C. voltage does not build up | Seating of brushes (slip rings and brushes) | Give slip ring brushes same attention as commutator brushes |
| Voltage unsteady but engine not missing | Poor commutation or brush contact at slip rings | See that brushes seat well on commutator, are free in holders, are not worn shorter than 3/4" and have good spring tension. If commutator is rough or badly grooved, return unit to depot for repairing |
| Voltage unsteady but engine not missing | Loose connections, especially in exciter circuits | Tighten connections |
| Voltage unsteady but engine not missing | Fluctuating load | Check load for unusual conditions. Correct any abnormal load condition causing trouble |
| Voltage unsteady but engine not missing | Some fluctuating loads, such as a motor driving a single action reciprocating pump, are normal conditions | Correct any abnormal load condition causing trouble |
| Generator overheating | Overloaded | Reduce load |
| Voltage drops under heavy load | Engine lacks power | See remedies for engine missing under heavy load |
| Voltage drops under heavy load | Cylinder compression | Tighten head gasket and spark plugs. If still not corrected, return unit to depot for repairs |
| Voltage drops under heavy load | Carburetor | Clean and adjust |
| Voltage drops under heavy load | Carburetor air cleaner | Clean and refill |
| Voltage drops under heavy load | Choke | See that it opens wide enough |
| Voltage drops under heavy load | Carbon in cylinders | Remove carbon |
| Voltage drops under heavy load | Restricted exhaust line | Clean or increase the size |
| Engine misses at light load | Carburetor idle adjustment set wrong or clogged | Adjust, clean if needed |
| Engine misses at light load | Spark plug gaps too narrow | Set at .030" |
| Engine misses at light load | Intake air leak (intake manifold) | Tighten or replace gaskets |
| Engine misses at light load | Faulty ignition (magneto) | Adjust or replace |
| Engine misses at light load | Uneven compression (cylinder compression) | Tighten head gasket and spark plugs. If still not corrected, return unit to depot for repairs |
| Engine misses at heavy load | Spark plugs defective | Replace |
| Engine misses at heavy load | Faulty ignition (magneto) | Adjust or replace |
| Engine misses at heavy load | Clogged carburetor jets | Clean |
| Engine misses at heavy load | Clogged fuel screen | Clean |
| Engine misses at heavy load | Defective spark plug cables | Replace |
| Engine misses at all speeds | Fouled spark plug | Clean and adjust |
| Engine misses at all speeds | Defective or wrong spark plug | Replace |
| Engine misses at all speeds | Sticking valves | Return unit to depot for repairs |
| Engine misses at all speeds | Broken valve spring | Replace |
| Engine misses at all speeds | Defective ignition wires | Replace |
| Engine misses at all speeds | Defective or improperly adjusted magneto | Adjust or replace |
| Low oil pressure | Oil too light | Drain, refill with proper oil |
| Low oil pressure | Oil badly diluted | Drain, refill with proper oil |
| Low oil pressure | Oil too low | Add oil |
| Low oil pressure | Oil relief valve not seating | Remove and clean |
| Low oil pressure | Badly worn engine bearings (smoky exhaust, excessive oil consumption which cannot otherwise be accounted for) | Return unit to depot for repairs |
| Low oil pressure | Sludge on oil screen | Remove and clean |
| Low oil pressure | Badly worn oil pump | Return unit to depot for checking |
| Low oil pressure | Defective oil gage | Return unit to depot for checking |
| High oil pressure | Oil too heavy | Drain, refill with proper oil |
| High oil pressure | Clogged oil passage | Return unit to depot for repairs |
| High oil pressure | Oil relief valve stuck | Remove and clean |
| High oil pressure | Low oil pressure gage (does not return to zero when unit not operating) | If not, install new oil pressure gauge |
| Engine backfires at carburetor | Lean fuel mixture (carburetor) | Clean carburetor |
| Engine backfires at carburetor | Lean fuel mixture (fuel screen) | Clean screen |
| Engine backfires at carburetor | Air leaks at intake manifold | Replace gaskets, tighten |
| Engine backfires at carburetor | Poor fuel | Drain, fill with good, fresh fuel |
| Engine backfires at carburetor | Spark too late (magneto timing) | Retime |
| Engine backfires at carburetor | Spark plug wires crossed | Install wires correctly |
| Engine backfires at carburetor | Intake valves leaking (hiss through carburetor when hand cranked with ignition off) | Return unit to depot for repairs |
| Excessive oil consumption, light blue smoky exhaust | Poor compression, usually due to leaking valves | Tighten head gasket and plugs. If still not corrected, return unit to depot for repairs |
| Excessive oil consumption, light blue smoky exhaust | Oil leaks from oil pan or connections (does not cause smoky exhaust) | Replace gaskets and leaking tubing. Tighten screws and connections |
| Excessive oil consumption, light blue smoky exhaust | Oil too light or diluted | Drain, refill with correct oil |
| Excessive oil consumption, light blue smoky exhaust | Bearing clearance too great (oil pressure registers low and this cannot otherwise be accounted for) | Return unit to depot for repairs |
| Excessive oil consumption, light blue smoky exhaust | Oil pressure too high | Refer to symptom of high oil pressure for remedies |
| Excessive oil consumption, light blue smoky exhaust | Engine misses firing (voltmeter reading unsteady and exhaust irregular) | Refer to symptoms of engine misses |
| Excessive oil consumption, light blue smoky exhaust | Faulty ignition (spark plugs) | Clean, adjust or replace |
| Excessive oil consumption, light blue smoky exhaust | Faulty ignition (magneto) | Repair, or replace |
| Excessive oil consumption, light blue smoky exhaust | Unit operated a great deal at light or no load | No remedy needed |
| Excessive oil consumption, light blue smoky exhaust | Too much oil | Drain excess oil |
| 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 adjustment) | Adjust |
| Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load | Carburetor float for leak and high level, needle valve for leak, jets for wear or damage, gasket washers for leaks | Install needed carburetor parts, adjust float level. Be sure all gaskets are in and tight |
| Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load | Choke not open | See that choke opens properly |
| Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load | Dirty carburetor air cleaner | Clean, refill to proper oil level |
| Light pounding knock | Connecting rod (short out one spark plug at a time to locate) | Return unit to depot for repairs |
| Light pounding knock | Low oil supply | Add oil |
| Light pounding knock | Low oil pressure | Refer to symptom of low oil pressure for remedies |
| Light pounding knock | Oil badly diluted | Change oil |
| Dull metallic thud. If not bad, may disappear after few minutes operation. If bad, increases with load | Loose crankshaft (no simple check; run under load) | Return unit to depot for repairs unless one of the next three remedies permanently correct the trouble |
| Sharp metallic thud, especially when cold engine first started | Low oil supply | Add oil |
| Sharp metallic thud, especially when cold engine first started | Low oil pressure | Refer to symptom of low pressure for remedies |
| Sharp metallic thud, especially when cold engine first started | Oil badly diluted | Change oil |
| Pinging sound when engine is rapidly accelerated or heavily loaded | Carbon in cylinders | Remove carbon |
| Pinging sound when engine is rapidly accelerated or heavily loaded | Spark too early (magneto timing) | Retime magneto |
| Pinging sound when engine is rapidly accelerated or heavily loaded | Wrong spark plugs | Install Champion 6M plugs |
| Pinging sound when engine is rapidly accelerated or heavily loaded | Spark plugs burned or carboned | Install new plugs |
| Pinging sound when engine is rapidly accelerated or heavily loaded | Valves hot | Return to depot for repairs |
| Pinging sound when engine is rapidly accelerated or heavily loaded | Fuel stale or low octane | Use good fresh fuel |
| Pinging sound when engine is rapidly accelerated or heavily loaded | Lean fuel mixture (carburetor) | Clean and adjust |
| Tapping sound | Tappet clearance too great | If too bad, return to depot for repairs |
| Tapping sound | Broken valve spring (engine mistiring) | Install new spring |
| Hollow clicking sound with cool engine under load | Loose pistons (put two teaspoonfuls heavy oil in cylinder; if noise disappears when engine warms up, indicates piston and rings need immediate attention) | If noise slight and disappears when engine warms up, no attention needed. Otherwise return unit to depot for repairs |
| Circuit breaker trips and disconnects load | Load too great | Reduce load |
| Circuit breaker trips and disconnects load | Load line short circuited | Remove short circuit |
| Light dim at far end of line but bright near power unit | Too small line wire for load and distance | Install larger or extra wires or reduce load |
| Motors run too slowly and overheat at far end of line but OK near power unit | Too small line wire for load and distance | Install larger or extra wires or reduce load |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Faulty ignition (spark plugs); Faulty ignition (magneto); Lack of fuel or faulty carburetion — fuel tank empty; Lack of fuel or faulty carburetion — carburetor adjustment. See the table for the matching fixes.
Documented causes: Poor compression, usually due to leaking valves; Oil leaks from oil pan or connections (does not cause smoky exhaust); Oil too light or diluted; Bearing clearance too great (oil pressure registers low and this cannot otherwise be accounted for). See the table for the matching fixes.
Documented causes: Oil too light; Oil badly diluted; Oil too low; Oil relief valve not seating. See the table for the matching fixes.