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Onan Modified Ford In-line 4 Engine

The Onan Modified Ford In-line 4 is an engine. It powers generator sets from Cummins/Onan, including the GGDB. It holds 4.5 L (1.2 gal) of oil.

Also known as: Onan Modified Ford In-line 4

4.5 L

Oil capacity

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

Engine specifications

Oil capacity	4.5 L

Generator sets powered by this engine

Cummins/Onan GGDB

Common problems

The Time Delay Start/Stop Module (A15) is malfunctioning.
Fix: Check for constant B+ at A15 terminal TB1-4. Check for run signal at ECM TB1-6. Voltage at A15 TB1-6 should be at B+ at the end of the start delay period. Check wiring and connections from A15 TB1-6 to ECM TB1-6.
The starter motor or solenoid is malfunctioning.
Fix: Push the Run-Stop-Remote switch to Run and check for battery voltage (B+) at starter solenoid terminal SW. Replace the starter motor if there is voltage but the motor does not function.
The Run-Stop-Remote switch (S12) or wiring is faulty.
Fix: A. Disconnect pin connector J4 from the ECM and check for electrical continuity (zero ohms) between switch terminals 2 and 3 when the switch is in the Run position and between terminals 1 and 2 when it is in the Remote position. Replace the switch if either set of contacts is faulty. b. If the switch works, check for electrical continuity (zero ohms) between J4-6 and J4-7 on the wire harness when the switch is in the Run position and between J4-5 and J4-7 when the switch is in the Remote position. Repair the wire harness if there is no electrical continuity in either position of the switch.
The OVERSPEED lamp comes on and the engine shuts down. 1
Fix: A. Reset the ECM by pushing the Run-Stop-Remote switch to Stop and the Reset switch to Reset and restart the set, monitoring engine speed. Spec A & B: Readjust the cutout speed if it is lower than specified. Replace the overspeed switch if it cannot be readjusted (see Section 3). Begin Spec C: If engine speed is correct and the set still shuts down, replace the ignition control module. b. Adjust the governor (see Section 8). c. If the governor cannot be adjusted to prevent shutdown due to overspeed, check for binding in the linkage. Repair and adjust the linkage as necessary. d. If the set still shuts down due to overspeed, re-install the magnetic speed pick-up unit to make sure the clearance with the flywheel gear teeth is correct. Replace the speed-pickup unit if output voltage at cranking speed is less than 1.5 VAC. (Intermittent open on magnetic speed pick-up lead can also cause an overspeed condition.) e. Replace the governor controller if the set still shuts down due to overspeed.
The grounding strap between the control box and the battery negative (-) terminal or the ground wire between the control and engine ground is loose, damaged or missing.
Fix: Check for continuity (zero ohms) between the grounding stud on the bottom of the control box and the battery negative (-) terminal. If there is no continuity or the grounding strap is loose or damaged, repair as necessary.
The engine shuts down due to over-speed.
Cause: The Fault Shutdown is being indicated by the fault circuit breaker reset button (extended out).
Fix: 5. Indicates engine has exceeded normal operating speed. Contact an authorized service center for service.
The engine shuts down due to low coolant level.
Cause: The Fault Shutdown is being indicated by the fault circuit breaker reset button (extended out).
Fix: 6. Indicates low coolant level. Replenish coolant and look for possible coolant leakage points and repair as required.
The engine shuts down due to high engine temperature or low coolant level.
Cause: The Fault Shutdown is being indicated by the fault circuit breaker reset button (extended out).
Fix: 3. Indicates engine has overheated (engine temperature has risen above 230° F/110° C). Allow engine to cool down completely before proceeding with the following checks: a. Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary. b. Check for obstructions to cooling airflow and correct as necessary. c. Check for a slipping fan belt and tighten if loose. d. Reset the tripped common fault circuit breaker. Contact an authorized service center for service if none of the above.
The engine does not crank in run mode
Cause: The Emergency Stop switch has been used. (The switch button is lit.)
Fix: Pull the Emergency Switch button. To reset the engine control, push the Run-Stop-Remote switch to Stop and the Reset switch to Reset. Then push the Run-Stop-Remote switch to Run to start the genset.
The engine does not crank in Remote mode.
Cause: The Run-Stop-Remote switch is at Stop. (The Switch-Off light will be flashing.); The Emergency Stop switch has been used. (The switch button is lit.); A Fault Shutdown is being indicated by one of the red lights on the control panel.; There is no remote circuit signal (12 VDC at auxiliary relay board A28-TB1-6) because fuse F3 on the ECM has blown.; There is no remote circuit signal (12 VDC at auxiliary relay board A28-TB1-6) because the remote circuit is not functioning properly.; Auxiliary relay board A28 is not functioning properly.
Fix: Push the Run-Stop-Remote switch to Remote.; Pull the Emergency Switch button. To reset the engine control, push the Run-Stop-Remote switch to Stop and the Reset switch to Reset. Then push the Run-Stop-Remote switch to Remote.; Service the set as necessary. To reset the engine control, push the Run-Stop-Remote switch to Stop and the Reset switch to Reset. Then push the Run-Stop-Remote switch to Remote.; a. Replace the fuse with one of the same type and amp rating (15 A). b. If fuse F3 blows again, find and repair the fault in the remote control circuit, such as a loose wire that may be shorting to ground or a shorted relay coil or other component. See Section 9 for remote connections.; Apply 12 VDC to A28-TB1-6. If the engine cranks, find and repair the fault in the remote control circuit. See Section 9 for remote connections.; Check for misconnections (see Section 9) or loose connections and replace auxiliary relay board A28 if there is 12 VDC at terminal A28-TB1-6 but not at A28-J2-6.
The engine cranks but does not start.
Cause: The engine is not getting fuel.; The air cleaner is blocked.; Fuse F2 on the ECM has blown.; Fuel solenoid K1 does not energize.
Fix: A. Open any closed fuel shutoff valve. b. Fill the propane supply tank. c. For natural gas fueled sets, check with the gas utility. d. Check fuel pressure at regulator (refer to Fuel Pressure in Section 8.) (High fuel pressure will prevent solenoid from opening.) e. Check fuel solenoid (VDC present at K1+ lead during cranking). Duel Fuel Sets Only: f. Check relay K99. Refer to wiring diagrams in Section 9. g. Check pressure switch wiring. Propane - normally closed connected to common. Natural gas - normally open connected to common. h. Check pressure switch function (@ 3.5 inch H2O or less, should switch from natural gas to LPG). i. Check S14 vacuum switch (optional) for proper operation.; Service as necessary.; Replace fuse with one of the same type and amp rating. If fuse F2 blows again, the wire between ECM TB1-10 and engine block terminal T26, or a wire between terminal T26 and an accessory may be loose or shorting to ground.; a. Fuel solenoid not energized by the ECM. Check for B+ at ECM TB1-10 when cranking. If no voltage present and fuse F2 is good replace ECM. b. Connect B+ to fuel solenoid (K1) terminal BAT. Replace the fuel solenoid if it does not “click” when energized. If fuel solenoid is working, check for blocked fuel line or fuel filter.
The ECM is faulty.
Fix: Push the Run-Stop-Remote switch to Run and check for battery voltage (12 VDC) at ECM TB1-8. Replace ECM if there is no voltage at ECM TB1-8 but 12 VDC at ECM TB1-9.
Temperature is causing too low a cranking speed for starting.
Cause: A. Increase room temperature. b. Plug in, repair or install engine coolant heater. c. Replace the engine oil if it is not of the recommended viscosity for the ambient temperature.
PRE LO OIL PRES lamp lights. Engine continues to operate. (Engine can be programmed to shut down.)
Fix: Indicates engine oil pressure has dropped to 20 psi (138 kPa). If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 5 procedure. If engine can be stopped, follow procedures in step 5.
PRE HI ENGINE TEMP lamp lights.
Fix: Indicates engine has begun to overheat and engine temperature has risen to approximately 220°F (104° C) or coolant level is low on optionally wired sets. If generator is powering non-critical and critical loads and cannot be shut down, use the following: a. Reduce load if possible by turning off non-critical loads. b. Check air inlets and outlets and remove any obstructions to airflow. If engine can be stopped, follow procedure in step 3.

Compiled from service & troubleshooting documentation across every generator set that uses the Onan Modified Ford In-line 4.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Battery	Ground		—	100 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
Clearance	Overspeed switch magnet-to-fly arm air gap (minimum)	0.005	inches (0.13 mm)	replace switch if less
Gap	Spark plug gap	0.044	inches
Pressure	Fuel changeover pressure switch	3.5	inch H2O or less	should switch from natural gas to LPG
Pressure	Fuel supply pressure (maximum permissible)	13.6	inches (350 mm) WC	operating or not operating
Pressure	Fuel supply pressure (minimum)	7	inches (178 mm) WC	genset operating at rated load
Pressure	Low fuel indicator	5	inches (127 mm) WC	single/dual fuel systems
Pressure	Low oil pressure shutdown (LOP)	14	psi (97 kPa)	naturally aspirated
Pressure	Low oil pressure shutdown (LOP)	25	psi (173 kPa)	turbocharged
Pressure	Natural gas energy content	1000	BTU per cubic foot
Pressure	Normal oil pressure	40 to 65	psi (276 to 449 kPa)	at normal operating temperature
Pressure	Pre-low oil pressure warning	20	psi (137 kPa)	naturally aspirated
Pressure	Pre-low oil pressure warning	30	psi (207 kPa)	turbocharged
Pressure	Propane energy content	2500	BTU per cubic foot
Resistance	Crank position sensor	315 to 385	ohms	Begin Spec C
Resistance	Exciter rotor winding resistance	0.49 to 0.59	ohms
Resistance	Exciter stator winding resistance (F1-F2)	13 to 16	ohms
Resistance	Ignition coil primary	0.5 to 1.3	ohms
Resistance	Magnetic speed pickup unit resistance	1,000 to 1,050	ohms
Resistance	Main rotor winding resistance (12-lead, 12.5 in)	2.75	ohms
Resistance	Main rotor winding resistance (12-lead, 13.75 in)	1.80	ohms
Resistance	Main rotor winding resistance (4-lead single-phase)	2.75	ohms
Resistance	Main stator winding resistance (12-lead three-phase)	0.104-0.115	ohms	reference stack 178 mm (7.0 in)
Resistance	Main stator winding resistance (12-lead three-phase)	0.108-0.119	ohms	reference stack 146 mm (5.75 in)
Resistance	Main stator winding resistance (4-lead single-phase)	0.053-0.059	ohms	reference stack 146 mm (5.75 in)
Resistance	Main stator winding resistance (6-lead 347/600 V three-phase)	0.47-0.51	ohms	reference stack 146 mm (5.75 in)
Resistance	Polarization index	at least 2	ratio (10 min / 1 min)
Resistance	Spark plug wires	6,000	ohms/foot
Resistance	Voltage adjusting rheostat	0 to approximately 1000	ohms	turning adjusting screw fully each way
Resistance	Winding insulation resistance (in service)	not less than 1	megohm
Resistance	Winding insulation resistance (new generator, dry windings)	at least 5	megohms	at 1 minute and 10 minutes
Speed	Governor arm angle	64	degrees (±2)	throttle lever closed
Speed	Governor idle speed	800	rpm	throttle closed by hand
Speed	Magnetic speed pickup unit back-off	1/4	turn	after touching ring gear tooth
Speed	Overspeed shutdown (ignition module)	2500	RPM	50/60 Hz sets, Begin Spec C
Speed	Overspeed shutdown (mechanical switch, 50 Hz sets)	2100	RPM	Spec A & B
Speed	Overspeed shutdown (mechanical switch, 60 Hz sets)	2500	RPM	Spec A & B
Speed	Start disconnect (electronic overspeed/start disconnect module)	about 660	rpm	Spec A & B
Speed	Starter disconnect	about 600	RPM
Temperature	High engine temperature shutdown	230	°F (110°C)
Temperature	Low engine temperature warning	65	°F (18°C)	selectable on Sensor board
Temperature	Low engine temperature warning (alternate)	90	°F (32°C)	selectable on Sensor board
Temperature	Normal coolant temperature	165 to 195	°F (74 to 91°C)	normal operating
Temperature	Pre-high engine temperature warning	220	°F (104°C)
Torque	Drive disc eight bolts	37-42	ft-lb (50-57 N-m)	remounting drive disc
Torque	Drive disc-to-flywheel six bolts	27-29	ft-lb (37-39 N-m)	remounting rotor to flywheel
Torque	End bell cover plate four screws	8	in-lb (3.8 N-m)
Torque	Exciter stator two mounting screws	8	ft-lb (11 N-m)	remounting exciter stator
Torque	Flywheel housing bolts	60	ft-lb (81 N-m)	remounting
Torque	Generator through-stud nuts (end bell)	19-21	ft-lb (26-28 N-m)	mounting end bell
Torque	Main rotor F1+/F2- terminal nuts	24	lb-in (2.7 N-m)	when reassembling
Torque	Overspeed switch center rotor bolt	18	ft-lbs (25 N-m)	when replacing the switch
Torque	Overspeed switch rotor bolt	18	ft-lb (25 N-m)	mounting rotor element/switch
Torque	Rotating rectifier diode terminal nuts	24	lb-in (2.6 N-m)
Voltage	B+ auxiliary terminals current (maximum)	7	amps	customer accessories at TB1-5
Voltage	Battery charging voltage	12 to 14	volts	normal
Voltage	Fully charged battery specific gravity	1.260	at 80°F (27°C)
Voltage	MAP sensor supply	5	VDC	between pins A and C of sensor plug
Voltage	MPU output at cranking speed (minimum)	1.5	VAC
Voltage	Oil pressure sender (replace if greater than)	3.1	VDC	across sensor terminals
Voltage	Temperature sender (replace if less than)	1.1	VDC	across sender terminals

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

Procedures

Electric Governor Adjustment adjustment

Tools: Tachometer or frequency meter

Check the dip switch (SW1-SW4) settings for the application frequency and spec.
Start the set, warm up under a partial load (at least 1/4 rated load), then disconnect all loads.
If the governor was replaced, adjust the Gain to approximately 5 and Stability to 3.5.
Adjust the Gain pot until the engine is stable and responsive; turn counterclockwise to eliminate hunting.
Bump the throttle lever a couple of times to check for hunting.
Apply full load and adjust the Stability pot to minimize overshoot.
Attach a tachometer or frequency meter and adjust the Speed Trim pot to the desired speed.
Shut down and restart the genset to check for overspeed shutdown on startup.

Gaseous Fuel Adjustments adjustment

⚠ Gaseous fuels are flammable and explosive and can cause severe personal injury or death. Keep a type ABC fire extinguisher handy.

Tools: Tachometer

Start the engine and let the set warm up under a partial load (at least 1/4 rated load).
Disconnect all loads, shut down, connect a tachometer and disconnect the governor linkage at the carburetor.
Start the engine and hold the throttle closed by hand so the engine does not overspeed.
Adjust the throttle idle position screw to obtain 800 rpm; reconnect the governor linkage.
Connect full rated load and turn the main fuel valve to full-rich.
Slowly turn the main fuel valve toward lean until the engine begins to lose speed.
Slowly back toward rich until the engine carries the full load smoothly.
For dual fuel, switch to LPG by closing the manual shutoff valve in the natural gas supply line.
Turn the LPG flow adjustment valve clockwise until the engine begins to lose speed.
Slowly turn it back counterclockwise until the engine carries full load smoothly.

Ignition Timing adjustment

Modification of connections is required only when converting the generator set fuel system.
Natural gas only (Spec A & B): connect EH lead P10 to IM pin #6.
Natural gas only (Spec A & B): connect EH lead P11 to IM pin #7.
LPG only (Spec A & B): connect EH lead P10 to IM pin #6; leave EH lead P11 and IM pin #7 disconnected.
Dual fuel (Spec A & B): connect EH lead P10 to IM pin #6; connect EH lead P11 to DFH lead P11; leave DFH lead P7 and IM pin #7 disconnected.
Begin Spec C: refer to the DC Wiring Diagram in Section 9.

Linkage Adjustment adjustment

With the genset stopped, remove the governor rod and spring from the throttle lever.
With the actuator shaft full counterclockwise, check the governor arm angle is 64° ±2°.
Loosen the governor arm screw to adjust the governor arm.
Verify the ball joint screw is in the third hole from the outside end of the governor arm.
Attach the governor rod and spring to the throttle lever.
With the throttle lever closed, adjust the governor rod so the arm angle is 64° ±2°.

Magnetic Speed Pickup Unit Adjustment adjustment

Tools: Ohmmeter

Measure MPU resistance; replace if not between 1,000 and 1,050 ohms.
With the MPU removed, rotate the ring gear until a tooth lines up in the center of the mounting hole.
Thread the pickup in gently by hand until it just touches the ring gear tooth.
Back it out 1/4 turn and set the locknut.
Check output voltage; replace the MPU if output voltage at cranking speed is less than 1.5 VAC.

Stability Adjustment adjustment

Run the generator set at rated frequency and no load.
Slowly turn the STABILITY pot clockwise until voltage becomes stable.
Turn counterclockwise until voltage again becomes unstable.
Turn the pot slightly clockwise from this position for maximum stability.
Readjust voltage after a stability adjustment.

UFRO Adjustment adjustment

Tools: Frequency meter

Check that the frequency selection jumper is connected for the application (50 Hz or 60 Hz).
Adjust the UFRO pot so the LED lights as frequency drops to 47 Hz (50 Hz) or 57 Hz (60 Hz).
Turn the pot clockwise to reduce the knee point frequency.

Voltage Adjustment adjustment

⚠ HAZARDOUS VOLTAGE! Touching uninsulated parts inside the control and power output boxes can result in severe personal injury or death.

Tools: AC-DC multimeter

Turn the voltage trimmer (Detector control) to its mid position.
Turn the VOLTS pot on the voltage regulator fully counterclockwise.
Turn the STABILITY pot on the voltage regulator to its mid position.
Start and operate the generator set at rated frequency and no load.
If the LED lights, see UFRO Adjustment.
Slowly turn the VOLTS pot clockwise until rated voltage is obtained.
See Stability Adjustment if voltage is unstable.

Testing Winding Insulation Resistance diagnostic

⚠ Disconnect starting battery cables (negative first) before performing tests.

Tools: 500 VAC megger

Apply the test potential between the winding and ground (winding laminations) for 10 minutes.
Record resistance at 1 minute and again at 10 minutes.
For a new generator with dry windings, obtain at least 5 megohms.
Polarization index should be at least 2.
For a set in service, resistance should not be less than 1 megohm.

Field Flashing repair

⚠ The voltage regulator could be damaged if the flashing circuit is connected for more than 5 seconds.

⚠ HAZARDOUS VOLTAGE! Stand on a dry wooden platform or rubber insulating mat, make sure clothing and shoes are dry, remove jewelry and use tools with insulated handles.

Tools: 12 volt battery, 10 ohm resistor, 18 volt voltage suppressor, 12 A, 300 V diode

Assemble a 12 volt battery, 10 ohm resistor, 18 volt voltage suppressor and 12 amp 300 volt diode.
While the set runs at nominal frequency, momentarily connect the positive (+) side to voltage regulator terminal VR21-F1 (X).
Connect the negative (-) side to voltage regulator terminal VR21-F2 (XX).
Check output voltage, shut down the set and restart it.

Generator Disassembly repair

⚠ The generator is heavy; you will need an assistant and hoist of sufficient capacity.

⚠ Disconnect battery charger from AC source before disconnecting battery cables.

⚠ Disconnect the negative (-) cable first and reconnect last.

Tools: Hoist and straps, Gear puller

Disconnect all power output and remote control connections and conduit; mark each lead.
Remove the end bell cover; disconnect the overspeed/start disconnect module plug and F1/F2 wires.
Remove the overspeed/start disconnect rotor element or overspeed switch assembly from the shaft end.
Disconnect generator leads and engine wiring harness from all terminals inside the control box.
Remove the four bolts securing the two saddle brackets of the control box to the generator.
Remove the two nuts and washers of the top generator through-studs.
Slide the control housing assembly off of the through-studs.
Cinch a hoisting strap around the middle of the generator stator and take up slack.
Scribe lines to register the parts before separating stator, flywheel housing and end bell.
Remove the remaining two through-stud nuts and tap the end bell free of the stator assembly.
Tap the generator stator free of the adaptor housing and draw it straight back.
Remove the generator through-studs.
Remove the air baffle, then the drive disc mounting bolts if rotor removal is needed.
Remove the two mounting screws if the exciter stator must be removed from the end bell.
Use a gear puller if the rotor bearing must be removed.

Generator Reassembly repair

⚠ Do not start the generator set until the DC start disconnect module has been remounted and reconnected.

Tools: Torque wrench

Press a new rotor bearing up to the shoulder of the shaft (do not lubricate); apply force to the inner race.
Torque the eight drive disc bolts to 37-42 ft-lb (50-57 N-m).
Torque the six drive disc-to-flywheel bolts to 27-29 ft-lb (37-39 N-m).
Install the air baffle using four bolts.
Torque the flywheel housing bolts to 60 ft-lb (81 N-m).
Thread generator through-studs into the flywheel housing with the short-thread ends in the housing.
Mate the generator stator and flywheel housing making the scribed index lines register.
Torque the exciter stator two screws to 8 ft-lb (11 N-m); connect F1 and F2 leads.
Wipe the bearing bore in the end bell with molybdenum disulfide grease; make sure the O-ring is in place.
Mount the end bell; torque the through-stud nuts to 19-21 ft-lb (26-28 N-m).
Mount the overspeed switch assembly on the rotor and torque the bolt to 18 ft-lb (25 N-m).
Remount and reconnect all other components disconnected or removed under Disassembly.
Route and reconnect the control box wires and F1/F2 leads to the stator connection board.
Secure the end bell cover plate and torque the four screws to 8 in-lb (3.8 N-m).

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

Connection	Leads	Notes
Spec A & B - Dual fuel (NG/LPG) only	Connect EH lead P10 to IM pin #6; connect EH lead P11 to DFH lead P11; leave DFH lead P7 and IM pin #7 disconnected	Ignition timing; required only when converting fuel system
Spec A & B - LPG only	Connect EH lead P10 to IM pin #6; leave EH lead P11 and IM pin #7 disconnected	Ignition timing; required only when converting fuel system
Spec A & B - Natural Gas (NG) only	Connect EH lead P10 to IM pin #6 (yellow/black with wire tie); connect EH lead P11 to IM pin #7 (yellow/black without wire tie)	Ignition timing; required only when converting fuel system

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 Onan Modified Ford In-line 4?

The Onan Modified Ford In-line 4 engine has an oil capacity of 4.5 liters.

Which generators use the Onan Modified Ford In-line 4 engine?

The Onan Modified Ford In-line 4 powers 1 generator set(s), including Cummins/Onan GGDB.

What is a common problem with the Onan Modified Ford In-line 4 engine?

A commonly reported issue on generators using the Onan Modified Ford In-line 4 is: The Time Delay Start/Stop Module (A15) is malfunctioning.. Fix: Check for constant B+ at A15 terminal TB1-4. Check for run signal at ECM TB1-6. Voltage at A15 TB1-6 should be at B+ at the end of the start delay period. Check wiring and connections from A15 TB1-6 to ECM TB1-6..