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Cummins/Onan 4-cyl. Engine

The Cummins/Onan 4-cyl. is an engine. It powers generator sets from Cummins/Onan, including the GEAA, GEAB and LSG-423. It holds 4.5 L (1.2 gal) of oil and 11.5 L (3.0 gal) of coolant.

Also known as: Onan Modified Ford 4-cyl.

4.5 L

Oil capacity

On this pageSpecs Generator sets Maintenance FAQ Torque & specs Procedures Wiring

Engine specifications

Oil capacity	4.5 L
Coolant capacity	11.5 L

Generator sets powered by this engine

Cummins/Onan GEAA Cummins/Onan GEAB Cummins/Onan LSG-423

How to read your Cummins/Onan engine serial & model number →

Common problems

Engine will not crank
Cause: Possible fault with control or starting system: Fault lamp on
Fix: Correct fault and reset control
The OVERLOAD lamp lights. Engine shuts down
Cause: The line circuit breaker is located in the ATS or generator set output box. If load exceeds generator current rating, the breaker will trip preventing the generator from being overloaded
Fix: Locate the source of overload and correct as necessary. Manually reset breaker to reconnect the load to the generator
PRE HET/LOP lamp lights. Engine continues to operate
Cause: Engine has begun to overheat and engine temperature has risen to approximately 205°F (97° C) or coolant level is low
Fix: If generator is powering non-critical and critical loads and cannot be shut down, use the following: Reduce load if possible by turning off non-critical loads; Check air inlets and outlets and remove any obstructions to airflow
LO OIL PRES lamp lights. Engine shuts down
Cause: Engine oil pressure has dropped to 25 psi (172 kPa)
Fix: Check oil level, lines and filters. If oil system is OK but oil level is low, replenish. Reset control and restart. Contact an authorized service center if oil pressure is not in the range of 40 to 65 psi (275 to 448 kPa)
SWITCH OFF lamp flashes
Cause: Run/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used
Fix: Move the Run/Stop/Remote switch to the Remote position for automatic starting
OVERCRANK lamp lights and engine stops cranking. or Engine runs, shuts down, and LO OIL PRES lamp lights
Cause: Possible fuel system problem
Fix: Check for empty fuel tank (LPG Vapor), fuel leaks, or plugged fuel lines and correct as required; Check for dirty fuel filter and replace if necessary (see Maintenance section); Check for dirty or plugged air filter and replace if necessary (see Maintenance section); Reset the control and restart after correcting the problem. Contact an authorized service center for service if none of the above
No AC output voltage
Cause: Field breaker is tripped
Fix: Reset breaker. Contact an authorized service center if voltage buildup causes breaker to trip
LO FUEL lamp lights. Engine continues to run....or LO FUEL lamp lights. Engine shuts down and LO OIL PRES lamp lights
Cause: Interruption of natural gas supply
Fix: Install the fuel hose and regulator supplied with the unit and connect to a propane fuel supply. Move the selector switch below control panel to the PROPANE position
HI ENG TEMP lamp lights. Engine shuts down
Cause: Engine has overheated (engine temperature has risen above 215°F/102°C) or coolant level is low
Fix: Allow engine to cool down completely before proceeding with the following checks: Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary; Check for obstructions to cooling airflow and correct as necessary; Check for a slipping fan belt and tighten if loose; Reset control and restart after locating and correcting problem. Contact an authorized service center if none of the above
Green RUN lamp lights following engine startup
Fix: Indicates all engine systems are normal. No corrective action required.
Fault lamp lights but no fault exists. Engine gauges show oil pressure, engine temperature, and frequency (speed) are within normal limits
Cause: The monitor board or a sensor may be at fault
Fix: Contact an authorized service center for service
Engine runs and then shuts down, OVERSPEED lamp lights
Cause: Engine has exceeded normal operating speed
Fix: Contact an authorized service center for service
The O/U VOLTAGE lamp lights. Engine shuts down
Fix: Contact an authorized service center for service
PRE HET/LOP lamp lights. Engine continues to operate. PRE HET/LOP
Cause: Engine has begun to overheat and engine temperature has risen to approximately 205°F (97°C) or coolant level is low.
Fix: A. Reduce load if possible by turning off non-critical loads. b. Check air inlets and outlets and remove any obstructions to airflow. 2A. Indicates engine oil pressure has dropped to 20 psi (137 kPa). If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 4. If engine can be stopped follow procedure in Steps 3 and 4.
OVERCRANK lamp lights and engine stops cranking. OVERCRANK
Fix: A. Check for empty fuel tank(LPG Vapor), fuel or leaks, or plugged fuel lines and correct as required.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 4-cyl..

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter	Replace annually or every 200 hours.		—	200 hr
Fuel filter	Spin off oil filter and discard it. Thoroughly clean filter mounting surface. Apply a thin film of oil to filter gasket and install new element. Spin element on by hand until gasket just touches mounting pad and then turn an additional 1/2 to 3/4 turn. Do not over-tighten (Figure 5-2).		—
Oil filter	Replace annually or every 200 hours.		—	200 hr
Battery	Check the battery connections to make sure they are clean and tight. A light coating of non-conductive grease will retard terminal corrosion.		—	90 hr
Belt	Inspect for wear or slippage, replace when worn or cracked.		—	90 hr
Coolant	Check for leaks and replace if necessary.	11.0 L	—	90 hr
Oil	Change annually or every 200 hours.	4.5 X1	—	200 hr
Spark plug	Check and replace annually.		—	365 hr

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Service specifications

Type	Item	Value	Unit	Condition
Gap	Speed sensor air gap	0.020	in. (0.508 mm)
Gap	Speed sensor air gap	0.36- 0.71	mm
Other	Exciter current delivery time (Fast-Response II)	0.05	seconds	change in load demand
Other	Overvoltage shutdown threshold	15% or more over nominal		shutdown after approximately one second
Pressure	Battery equalizer input voltage (24 volts nominal)	20- 35	volts
Pressure	Battery equalizer output voltage	(input voltage/2) ±2%	volts
Pressure	Low oil pressure shutdown (diesel models)	5.5 to 10.5	psi (38 to 72 kPa)
Pressure	Low oil pressure shutdown (gasoline models)	11.5 to 18.5	psi (79 to 126 kPa)
Pressure	Pressure switch 364345	483 ±14	kPa
Resistance	CR relay coil resistance	approximately 125	Ohms	12-Volt coil; measure between terminals A and B
Resistance	CR relay normally closed contacts (continuity)	1-7, 2-8, 3-9
Resistance	Exciter armature low resistance reading (faulty if below)	under 0.1-0.2	ohms
Resistance	Generator field F3-F4 continuity	2-3.75	ohms, +5%
Resistance	Photo transistor board reading (covered)	300K	ohms or higher	covered
Resistance	Photo transistor board reading (lit)	5K	ohms or lower	bright flashlight on board
Resistance	Pressure sender 264390 value A	240 +17/- 15	ohms at 0 psi
Resistance	Pressure sender 264390 value B	153 +12/- 15	ohms at 25 psi
Resistance	Pressure sender 264390 value C	33.5	ohms at 100 psi
Resistance	Pressure sender 365624 value A	241 ±16	ohms at 0 psi
Resistance	Pressure sender 365624 value B	152 ±13	ohms at 50 psi
Resistance	Pressure sender 365624 value C	33.5	ohms at 200 psi
Resistance	Temperature sender 226717 value A	123.8 +7.2/- 7.8	ohms at 90.6 C (195 F)
Resistance	Temperature sender 226717 value B	35.6 +3.4/- 3.6	ohms at 137.8 C (280 F)
Resistance	Temperature sender 226919 value A	942 ±22	ohms at 37.7 C (100 F)
Resistance	Temperature sender 226919 value B	35	ohms at 115.6 C (240 F)
Speed	Governed speed (50 Hz models)	1500	rpm
Speed	Governed speed (60 Hz models)	1800	rpm
Speed	Governor speed droop	3 Hz or 90 rpm		between no load and full load
Speed	No-load frequency (50 Hz operation)	53	Hz	no load
Speed	No-load frequency (60 Hz operation)	63	Hz	no load
Speed	Overspeed shutdown	70	Hz	60 Hz models
Speed	Overspeed shutdown (50 Hz sets)	60	Hz
Speed	Overspeed shutdown (60 Hz sets)	70	Hz
Temperature	Battery equalizer operating temperature	- 40 to 71	C (- 40 F to 160 F)
Temperature	Low water temperature start-up threshold	below 70	°F (21°C)	10-second start-up
Temperature	Temperature switch 241308	107 ±4	C (225 F ±7 F)	normally open to close on temp. rise
Temperature	Temperature switch 290090/GM51705	16 ±3	C (60 F ±5 F)	normally open to close on temp. fall
Torque	Drive disc mounting bolts	50	ft. lbs. (108.48 Nm)
Torque	FR Activator mounting screws	20-26	in. lbs. (2.8-2.8 Nm)
Torque	FR Activator terminal screws A and F	20-25	in. lbs. (2.3-2.8 Nm)
Torque	Fan bolts	260	in. lbs. (29.4 Nm)
Voltage	1CR relay test voltage at P5 pin 10 to ground	0.5 to 1.0	volts	on-crank cycle
Voltage	Battery high volts lamp setpoint (12-volt systems)	15	volts
Voltage	Battery high volts lamp setpoint (24-volt systems)	30	volts
Voltage	Battery low volts lamp setpoint (12-volt systems)	10	volts
Voltage	Battery low volts lamp setpoint (24-volt systems)	20	volts
Voltage	CR relay test voltage at P5 pin 9 to ground	0.5 to 1.0	volts	Generator Master Switch in TEST position
Voltage	High voltage test (exciter armature A1 or A2 to rotor shaft)	4,100	volts AC	not more than one second
Voltage	High voltage test (generator field F3 or F4 to shaft)	1,100	volts AC	not more than one second; do not repeat test
Voltage	LED board output at 3B(+) and 5B(-)	1-2	Volts DC	generator set running
Voltage	Speed sensor voltage, wire 2 (black) & 16 (white)	3- 6	volts DC
Voltage	Speed sensor voltage, wire 2 (black) & 24 (red)	8- 10	volts DC

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

Bosch Electronic Governor Stability and Gain Adjustment adjustment

Check that the stability control is in its extreme counterclockwise position.
Start engine. Allow the governor to control the engine. If engine is unstable, turn the gain control counterclockwise until stability is obtained. Adjust speed screw to proper engine speed.
Turn the gain control clockwise until the engine becomes just unstable. Back the gain control slightly counterclockwise until the engine is again stable.
Turn the stability control clockwise until the engine becomes just unstable. Back the stability control slightly counterclockwise until the engine is again stable.

Diesel Mechanical Governor Frequency Adjustment adjustment

Tools: Frequency meter

Start the generator set, observe the frequency meter.
Loosen the fuel pump high speed screw locknut to make the adjustments.
To increase or decrease the frequency (at no load), rotate the screw clockwise or counterclockwise respectively.
Tighten the locknut.
Loaded droop frequency may alternately be adjusted to the operating frequency at full load.

Gas/Gasoline Mechanical Governor Speed and Sensitivity Adjustment adjustment

Tools: Hand tachometer, Frequency meter

With the set running at full or rated load, check speed with hand tachometer or frequency meter.
Loosen locking nut on speed adjusting screw; turn clockwise to increase speed (and frequency) or counterclockwise to decrease; lock nut at new setting.
For sensitivity, loosen the nut at bottom of adjusting eyebolt and tighten the top nut to draw the head of the eyebolt closer to the governor arm pivot point (more sensitive).
To make governor control less sensitive, loosen the top nut and tighten the bottom nut to move the head away from the pivot point.
Recheck speed after sensitivity adjustment since changing this will also affect speed.

Generator Frequency Change (60 Hz to 50 Hz) adjustment

Tools: Frequency meter

On Microcomputer equipped generators, snip the jumper indicated in Figure A1 to convert from 60 Hz to 50 Hz.
Check frequency meter for a no load reading of 63 Hz for 60 Hz operation and 53 Hz for 50 Hz operation.
If equipped with isochronous governor, check for 60 and 50 Hz operation at no load.
If no frequency meter, connect meter across VO and V7 on control board terminal strip (set must not be running while making connection).

High and Low Battery Voltage Indicator Adjustment adjustment

Tools: DC power supply

Move Generator Master Switch to AUTO position. SYSTEM READY lamp should go on.
Rotate potentiometers R42 (High Batt. Volts) and R25 (Low Batt. Volts) fully counterclockwise.
Set DC power supply at 10 volts (20 volts for 24-volt units). Slowly rotate pot R25 clockwise until BAT. LOW VOLTS lamp lights.
Set DC power supply at 15 volts (30 volts for 24-volt units). Slowly rotate pot R42 clockwise until BAT. HIGH VOLTS lamp lights.
Set DC power supply between 10 to 15 volts (20 to 30 volts for 24-volt units). SYSTEM READY lamp should be on.
Seal pots after settings have been established.

Overfrequency Adjustment (Over/Underfrequency Relay, Decision-Maker 3+) adjustment

Turn the overfrequency adjustment potentiometer fully clockwise (CW).
Place master switch in RUN to start the generator set.
Adjust governor per engine operation manual, engine service manual, or governor section of this manual.
Slowly turn overfrequency potentiometer counterclockwise (CCW) until the LED starts flashing; after about 10 seconds the set shuts down on auxiliary fault.
Place master switch to OFF/RESET to reset the controller.
Place master switch to RUN to start the generator set.
Readjust the governor to the desired frequency as required.
Place master switch to OFF/RESET to stop the generator set.

Overvoltage Feature Testing and Adjustment (Decision-Maker 3+) adjustment

⚠ Hazardous voltage. Moving parts. Will cause severe injury or death. Operate the generator set only when all guards and electrical enclosures are in place.

⚠ Disconnecting the electrical load. Hazardous voltage will cause severe injury or death.

Disconnect generator set from load by opening line circuit breaker or disconnecting and taping output leads.
Determine overvoltage shutdown value based on user requirement; factory setting is 15% above nominal line-to-neutral voltage.
Remove the controller cover.
Place master switch in RUN to start the generator set.
Observe AC voltmeter; turn voltage adjustment potentiometer CW until generator set shuts down.
If the shutdown point is correct, go to step 12; otherwise continue.
Turn controller circuit board R42 adjustment potentiometer fully CW.
Place master switch to OFF/RESET to reset; then to RUN to start.
Observe AC voltmeter while turning voltage adjustment potentiometer to desired overvoltage shutdown point.
Turn R42 adjustment potentiometer slowly CCW until the generator set shuts down.
Turn controller voltage adjustment potentiometer slightly CCW.
Place master switch OFF/RESET then RUN to start; adjust for correct voltage and phase.
Place master switch OFF/RESET to stop.
Disconnect battery negative lead first; reconnect generator set to load; reconnect battery negative lead last.

Reactive Droop Compensator Adjustment Procedure adjustment

Tools: Voltmeter, Wattmeter

Remove any load; start each generator set with master switch in RUN.
Set reactive droop compensator rheostat on generator set no. 1 to minimum CCW; record rpm/frequency and voltage at 1/4 load steps to full load.
Repeat for generator set no. 2.
Compare readings; adjust voltage within 1 volt and speed within 3 rpm (or 0.1 Hz) at each load step.
Check droop compensation on each unit with an inductive load 1/2 to full load.
Adjust rheostat to approximately 4% below rated voltage at full load.
Repeat for unit no. 2.

Reactive Droop Compensator Alternate Adjustment Procedure adjustment

Tools: Voltmeter

Turn reactive droop compensator rheostat on generator set no. 1 to minimum setting.
Remove controller cover; move voltage sensing lead from V7 to V9 at the AC fuse terminal block.
Remove any load connected to the generator set.
Start the generator set with master switch in RUN.
Use controller or remote voltage adjusting potentiometer to fine adjust voltage.
Apply resistive load (1.0 power factor) until reaching rated current.
Adjust reactive droop compensator rheostat to achieve a 4% droop in voltage.
Remove the resistive load and stop the generator set.
Return voltage sensing lead from V9 to V7 at the AC fuse terminal block.
Replace the controller cover and repeat for generator set no. 2.

Underfrequency Adjustment (Over/Underfrequency Relay, Decision-Maker 3+) adjustment

Turn underfrequency adjustment potentiometer fully clockwise (CW).
Place master switch in RUN to start the generator set.
Adjust governor per engine operation manual, engine service manual, or governor section of this manual.
Slowly turn underfrequency potentiometer counterclockwise (CCW) until LED starts flashing; after about 10 seconds the set shuts down on auxiliary fault.
Place master switch to OFF/RESET to reset the controller.
Place master switch to RUN to start the generator set.
Readjust the governor to the desired frequency as required.
Place master switch to OFF/RESET to stop the generator set.

2-Wire Low Water Level Sender Test diagnostic

⚠ Hot engine and exhaust system can cause severe injury or death. Do not work on the generator set until it cools.

⚠ Hazardous voltage. Moving parts. Will cause severe injury or death. Operate the generator set only when all guards and electrical enclosures are in place.

Tools: DC voltmeter

Measure DC voltage between lead 31A (+) and ground (- ) with sender submerged in coolant; voltmeter indicates approximately 12.5 VDC.
Measure DC voltage between lead 31A (+) and ground (- ) with sender removed from coolant for at least 5-15 seconds; voltmeter indicates a drop to approximately 7 VDC.

3-Wire Low Water Level Sender Test diagnostic

⚠ Hot engine and exhaust system can cause severe injury or death. Do not work on the generator set until it cools.

⚠ Hazardous voltage. Moving parts. Will cause severe injury or death.

Tools: Ohmmeter

Measure resistance between lead 31 and ground with sender submerged in coolant; ohmmeter indicates a high resistance reading.
Measure resistance between lead 31 and ground with sender removed from coolant for at least 5-15 seconds; ohmmeter indicates a low resistance reading.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Voltage reconnection

Voltage	Phase	Connection	Notes
120/208 or 139/240	3-Phase	4-Wire Low Wye	60Hz, 120/208-Volt or 139/240-Volt 3-Phase, 4-Wire Low Wye; 50Hz, 120/208-Volt or 110/190-Volt 3-Phase, 4-Wire Low Wye
120/240	1-Phase	3-Wire	60Hz, 120/240-Volt, 1-Phase, 3-Wire; 50Hz, 110/220-Volt, 1-Phase, 3-Wire
120/240	3-Phase	4-Wire Delta	60Hz, 120/240-Volt, 3-Phase, 4-Wire, Delta; 50Hz, 110/220-Volt, 3-Phase, 4-Wire, Delta. CT3 - Not Used
277/480	3-Phase	4-Wire High Wye	60Hz, 277/480-Volt, 3-Phase, 4-Wire High Wye; 50Hz, 220/380-Volt, 3-Phase, 4-Wire High Wye

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Common questions

What is the oil capacity of the Cummins/Onan 4-cyl.?

The Cummins/Onan 4-cyl. engine has an oil capacity of 4.5 liters.

Which generators use the Cummins/Onan 4-cyl. engine?

The Cummins/Onan 4-cyl. powers 3 generator set(s), including Cummins/Onan GEAA, Cummins/Onan GEAB, Cummins/Onan LSG-423.

How often should you change the oil in the Cummins/Onan 4-cyl.?

The Cummins/Onan 4-cyl. oil change interval is every 200 hours.

What is a common problem with the Cummins/Onan 4-cyl. engine?

A commonly reported issue on generators using the Cummins/Onan 4-cyl. is: Engine will not crank. Cause: Possible fault with control or starting system: Fault lamp on. Fix: Correct fault and reset control.