Home› Troubleshooting›Cummins/Onan ED series

Cummins/Onan ED series Troubleshooting

Cummins/Onan ED series troubleshooting: 121 symptom-cause-remedy entries from the manufacturer's own service documentation.

Cummins/Onan ED series — full specs, parts & maintenance.

All Cummins/Onan fault codes →

Troubleshooting

121

Symptoms & remedies

Symptom	Cause	Remedy
Generator overheating	Overloaded	Reduce load.
Generator overheating	Brush rig out of position	Be sure to line up marks.
Voltage drops under heavy load	Engine lacks power	See remedies for engine missing under heavy load.
Voltage drops under heavy load	Poor compression	Tighten cylinder head and spark plugs. If still not corrected, grind the valves. Replace piston rings, if necessary.
Voltage drops under heavy load	Faulty carburetion	Check the fuel system. Clean, adjust, or replace parts necessary.
Voltage drops under heavy load	Restricted air cleaner	Clean and refill.
Voltage drops under heavy load	Excessive choking	See that choke opens properly.
Voltage drops under heavy load	Carbon or lead in cylinder	Remove carbon.
Voltage drops under heavy load	Restricted exhaust line	Clean or increase the size.
Engine misfires at light load	Carburetor idle adjustment set wrong or clogged	Adjust, clean if needed.
Engine misfires at light load	Spark plug gaps too narrow	Adjust to correct gap.
Engine misfires at light load	Intake air leak	Tighten or replace gaskets.
Engine misfires at light load	Faulty ignition	Clean, adjust, or replace breaker points, plugs, condenser, coil, etc., or retime ignition.
Engine misfires at light load	Uneven compression	Tighten cylinder head and spark plugs. If still not corrected, grind valves. Replace piston rings, if necessary.
Engine misfires at light load	Worn intake valve stems or guides	Replace valves or guides.
Engine misfires at heavy load	Spark plugs defective	Replace.
Engine misfires at heavy load	Faulty ignition	Clean, adjust, or replace breaker points, plugs, condensers, coil, etc., or retime ignition.
Engine misfires at heavy load	Clogged carburetor	Clean jets.
Engine misfires at heavy load	Clogged fuel screen	Clean.
Engine misfires at heavy load	Valve lash too tight	Adjust.
Engine misfires at heavy load	Defective spark plug cables	Replace.
Engine misfires at all loads	Fouled spark plugs	Clean and adjust.
Engine misfires at all loads	Defective or wrong spark plug	Replace.
Engine misfires at all loads	Sticking valves	Clean stems and guides.
Engine misfires at all loads	Broken valve spring	Replace.
Engine misfires at all loads	Defective ignition wires	Replace.
Engine misfires at all loads	Defective or improperly adjusted points	Adjust or replace breaker points.
Engine misfires at all loads	Defective ignition condenser	Replace.
Engine misfires at all loads	Improper valve lash	Adjust.
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, or replace.
Low oil pressure	Badly worn engine bearings	Replace.
Low oil pressure	Sludge on oil inlet screen	Remove and clean screen.
Low oil pressure	Badly worn oil pump	Repair or replace pump.
Low oil pressure	Defective oil pressure gauge	Replace engine or panel unit.
High oil pressure	Oil too heavy	Drain, refill with proper oil.
High oil pressure	Clogged oil passage	Clean all lines and passages.
High oil pressure	Oil refill valve stuck	Remove and clean.
High oil pressure	Defective oil pressure gauge	Replace engine or panel unit.
Plant starts but does not continue to run	Start button released too soon	Hold in contact longer.
Plant starts but does not continue to run	Defective charging generator	Repair.
Plant starts but does not continue to run	Defective panel equipment	See Controls.
Engine backfires at carburetor	Lean fuel mixture	Clean or adjust carburetor.
Engine backfires at carburetor	Clogged fuel screen	Clean screen.
Engine backfires at carburetor	Intake air leak	Replace flange gaskets, tighten carburetor.
Engine backfires at carburetor	Poor fuel	Refill with good, fresh fuel.
Engine backfires at carburetor	Spark too late	Retime ignition.
Engine backfires at carburetor	Spark plug wires crossed	Install wires correctly.
Engine backfires at carburetor	Intake valves leaking	Grind or replace.
Excessive oil consumption, light blue smoky exhaust	Sludged rings, excessive bearing clearances, piston skirt collapsed, worn intake valve guides	Replace worn parts.
Excessive oil consumption, light blue smoky exhaust	Oil leaks from engine or connections (this does not cause smoky exhaust)	Replace gaskets or 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	Too large bearing clearance	Replace bearings.
Excessive oil consumption, light blue smoky exhaust	Oil pressure too high	Refer to symptoms of high oil pressure for remedies.
Excessive oil consumption, light blue smoky exhaust	Engine misfires	Refer to symptoms of engine misfires.
Excessive oil consumption, light blue smoky exhaust	Faulty ignition	Clean, adjust, or replace breaker points, plugs, condenser, coil, etc., or retime ignition.
Excessive oil consumption, light blue smoky exhaust	Unit operated at light or no load for long periods	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	Be sure all jet gaskets are in place and tight; and float needle valve gasket is in place and tight. Adjust choke. Install needed carburetor parts, adjust float level.
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 level.
Light pounding knock	Loose connecting rod bearing	Replace.
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.
Engine stops unexpectedly	Fuel tank empty	Refill.
Engine stops unexpectedly	Fuel pump failure	Repair or replace.
Engine stops unexpectedly	High water temperature	See symptoms for engine overheating.
Engine stops unexpectedly	Defective ignition	Check the ignition system. Repair or replace parts necessary.
Dull metallic thud, if not bad, may disappear after few minutes operation. If bad, increases with load	Loose crankshaft	Replace bearings, unless one of the next three remedies permanently corrects 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	Retime ignition.
Pinging sound when engine is rapidly accelerated or heavily loaded	Wrong spark plugs	Install correct 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	Adjust tappet clearance.
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	Clean or adjust carburetor.
Engine cranks too stiffly	Corroded terminals	Clean and tighten terminals.
Engine cranks too stiffly	Too heavy oil in crankcase	Drain, refill with light oil.
Engine cranks too stiffly	Weak battery	Test and recharge or replace battery.
Engine cranks too stiffly	Engine stuck	Disassemble and repair.
Engine cranks too stiffly	Defective cable	Install new cable.
Engine will not start when cranked	Faulty ignition	Clean, adjust, or replace breaker points, plugs, condenser, coil, etc., retime ignition.
Engine will not start when cranked	Lack of fuel or faulty carburetion	Refill the tank. Check the fuel system. Clean, adjust or replace parts necessary.
Engine will not start when cranked	Clogged 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	Tighten cylinder head and spark plugs. If still not corrected, grind the valves. Replace piston rings, if necessary.
Engine will not start when cranked	Wrong timing	Retime ignition.
Engine will not start when cranked	Poor choking	If plant is cold, adjust choke. If plant is warm, pull up on choke arm momentarily, while cranking.
Engine runs but current does not build up	Poor brush contact or dirty commutator or slip rings	See that brushes seat well, are free in holders, are not worn too short, and have good spring tension.
Engine runs but current does not build up	Open circuit, short circuit or ground in generator	See GENERATOR, replace part necessary.
Current unsteady but engine not misfiring	Speed too low	Adjust governor to correct speed.
Current unsteady but engine not misfiring	Poor commutator or brush contact	See that brushes seat well on commutator and slip rings, are free in holders, are not worn too short, and have good spring tension.
Current unsteady but engine not misfiring	Loose connections	Tighten connections.
Current unsteady but engine not misfiring	Fluctuating load	Correct any abnormal load condition causing trouble.
Tapping sound	Tappet clearance too great	Adjust or replace tappets.
Tapping sound	Broken valve spring	Install new spring.
Hollow clicking sound with cool engine under load	Loose pistons	If noise only slight and disappears when engine warms up, no immediate attention needed. Otherwise replace worn parts.
Voltage low at far end of line but normal 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.
Noisy brushes	High mica between bars of commutator	Undercut mica.
Excessive arcing at the brushes	Rough commutator or rings	Turn down.
Excessive arcing at the brushes	Dirty commutator or rings	Clean.
Excessive arcing at the brushes	High mica	Undercut mica.
Excessive arcing at the brushes	Brush rig out of position	Line up marks on brush rig and support.
Engine overheating	Low water in radiator	Refill radiator.
Engine overheating	Overloaded	Remove part of load.
Engine overheating	Improper lubrication	See Low Oil Pressure.
Engine overheating	Radiator obstructed	Clean radiator.
Engine overheating	Ignition timing late	Adjust ignition timing.
Engine overheating	Improper ventilation	Provide for better air change.
Starter will not crank engine	Discharged battery	Test and recharge or replace battery.
Starter will not crank engine	Corroded terminals	Clean and tighten terminals.
Starter will not crank engine	Loose connections	Tighten connections.
Starter will not crank engine	Defective starter relay	Clean contacts if necessary. Replace switch if necessary.

Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.

Cross-brand guides for these symptoms

Low oil pressure High oil pressure

Common questions

Cummins/Onan ED series: Excessive oil consumption, light blue smoky exhaust — what causes it?

Documented causes: Sludged rings, excessive bearing clearances, piston skirt collapsed, worn intake valve guides; Oil leaks from engine or connections (this does not cause smoky exhaust); Oil too light or diluted; Too large bearing clearance. See the table for the matching fixes.

Cummins/Onan ED series: Engine misfires at all loads — what causes it?

Documented causes: Fouled spark plugs; Defective or wrong spark plug; Sticking valves; Broken valve spring. See the table for the matching fixes.

Cummins/Onan ED series: Low oil pressure — what causes it?

Documented causes: Oil too light; Oil badly diluted; Oil too low; Oil relief valve not seating. See the table for the matching fixes.