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Cummins/Onan MDJF Engine

The Cummins/Onan MDJF is a 2.3 L naturally aspirated engine rated at 1800 rpm. It powers generator sets from Cummins/Onan, including the 15.0MDJF and 15.0MDJF-3CR. It holds 6.2 L (1.6 gal) of oil and 2 L (0.5 gal) of coolant.

Also known as: Onan MDJF

2.3 L

Displacement

1800 rpm

Rated speed

6.2 L

Oil capacity

On this pageSpecs Generator sets FAQ Service intervals Torque & specs Fluids Procedures Wiring

Engine specifications

Oil capacity	6.2 L
Coolant capacity	2.0 L
Displacement	2.3 L
Aspiration	naturally aspirated
Rated speed	1800 rpm

Generator sets powered by this engine

Cummins/Onan 15.0MDJFCummins/Onan 15.0MDJF-3CR

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

Troubleshooting

Fault codes

Code	Meaning
e008	No specific name provided for e008
10	Overload

Symptoms & remedies

Symptom	Cause	Remedy
Engine does not crank.	Battery dead, loose connections, incorrect wiring, or faulty starter motor.	Check 12 VDC to ground at battery BT1 and at starter motor Bl. Check B+ present at TB11, K13, S1, and M11. Check battery cables for polarity and tightness at battery and starter motor. If battery is dead, check if centrifugal switch S1 is open to ground. Replace S4 or charge battery. Jumper battery cable connection to ground at starter. Check starter motor. With S11 at START, jumper K11 contacts to starter solenoid. Start relay K11 is defective; replace it.
Engine cranks but does not start.	Faulty switch or lead connections.	Check 12 VDC present between start terminal on S11 and ground (TB11-1) with S11 at START. Check 12 VDC present between M11-B+ and ground TB11-1 with S11 at START. Replace faulty switch S11 if necessary. Check lead from TB12-4 to fuel pump; check fuel pump and replace if necessary.
Engine starts but stops when start switch is released.	Faulty switch or lead connections.	Connect voltmeter from 12 VDC to ground at battery BT1 and at starter motor Bl. Check B+ present at TB11, K13, S1, and M11. Check battery cables for polarity and tightness at battery and starter motor. If battery is dead, check if centrifugal switch S1 is open to ground. Replace S4 or charge battery. Jumper battery cable connection to ground at starter. Check starter motor. With S11 at START, jumper K11 contacts to starter solenoid. Start relay K11 is defective; replace it.
No build up of AC output voltage.		Is Field Breaker CB21 on control panel ON? If not, step 2. Connect jumper wire across terminals of Field Breaker, CB21. Does AC output voltage build up? If yes, replace Field Breaker. If no, push to reset Field Breaker. Does AC output voltage build up? If yes but is high, low, unstable, or causes tripping of Field Breaker, refer to Tables B, C, or D. If no, step 4. Disconnect alternator stator leads 1 & 2 from TB21-1 and TB21-2 on VR22. Is reference voltage across 1 & 2 20 VAC or more? If not, refer to step 14.
AC output voltage builds up, but is unstable.		Are there any loose or broken wires or connections on voltage regulator assembly VR22? If yes, step 3. Is W9 (exciter field) wiring harness from VR22 to End bell OK? If no, replace PC Board VR21. Do not replace the printed circuit board until the trouble not on the PC board has been located and corrected to avoid damage to new PC board.
AC output voltage builds up, but is high or low.		Is set running at correct RPM? (See appropriate engine manual to set RPM) If no, step 3. Does adjustment of Voltage Adjusting knob for R22 on VR22 result in correct output voltage? If no, step 4. Does adjustment of potentiometer R26 on VR21 result in correct output voltage? If no, refer to step 5. Is correct voltage reference V4 to V1, V2, or V3 on VR21 being used? Refer to Figure 6. If no, replace voltage regulator PC board VR21. Do not replace the printed circuit board until the trouble not on the PC board has been located and corrected to avoid damage to new PC board.
AC output voltage builds up, but Field Breaker trips.		Does AC output voltage build up to 140% or more of rated voltage before Field Breaker trips? If yes, are there any loose or broken wires or connections on VR22? If no, is diode CR15 on VR21 OK? If no, are T21 windings and connections OK? If no, are generator stator leads properly connected? Refer to Figure 6. Replace VR21 if necessary. Are diodes CR1, CR2, CR3, CR4, CR5, CR6 in rotating rectifier assemblies OK? Check all diodes - more than one may be defective. Is brushless exciter stator winding OK? Is generator rotor field winding OK? If no, is brushless exciter rotor windings OK?

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

Common problems

Water or foreign material in the fuel can ruin the injection system.
Cause: If daily inspection shows water or dirt in the fuel pump sediment bowl
Fix: Fuel handling and storage facilities should be checked and situation corrected. Fi Iter elements should be replaced following corrections of fuel contamination problems.
This service must be conducted by trained diesel injection equipment personnel with suitable test facilities.
Fix: Omit this service until these conditions can be met.
Slip ring brushes not contacting the slip rings.
Fix: Replace slip ring brush spring which may have come off or broken; or replace brushes which may have become worn down to far to contact the slip rings.
Short circuit in field
Cause: Dampness or deteriorated insulation.
Fix: Bake if damp, repair or replace if insulation is deteriorated.
Overload 10
Open circuit in field
Cause: Rough usage or original short circuit which may have burned a coil or connection.
Fix: Examine field connections and test with ohmmeter. If a coil is open, replace it.
No specific name provided for e008 e008
No generator output or low output.
Cause: Defective shunt field bridge rectifier
Fix: Check AC components as listed above and preceding page. Check bridge rectifier with an ohmmeter. Replace if necessary.
No battery charger output (1 amp normal).
Cause: Diode CR2 bad.
Fix: Open component in charging circuit. Check diode with an ohmmeter and replace if open or shorted.
Insulating film on slip rings.
Fix: Clean slip rings with stone or fine sandpaper and blow out dust.
Incomplete circuit between exciter and slip rings.
Cause: Slip ring brush shunt broken
Fix: Check all slip ring brush shunts with an ohmmeter and replace broken brush shunts.
Faulty load
Cause: Open circuit or short circuit on line.
Fix: Check line and load and the load.
Ammeter indicating ‘O’
Cause: Generator has not built up voltage
Fix: Check the automatic field flash circuit which receives power from the § terminal of the start solenoid. When the start solenoid is energized, power should be applied to the static exciter and revolving field for faster voltage build-up.
AC stator winding shorted
Cause: Insulation or coils broken.
Fix: Rewind or replace stator winding.
AC stator winding open
Cause: Original short circuit may have burned a coil or connection.
Fix: Test with an ohmmeter and if open, rewind or replace with a new stator winding.

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

Repair guides

Step-by-step procedures compiled from the Cummins/Onan service manual for this engine.

Service intervals

Item	Action	Hours	Months	Notes
Exhaust system	Inspect	8 hr		With plant running, visually and audibly check for leaks
Fuel sediment bowl	Drain	8 hr
Fuel supply	Check	8 hr
Oil level	Check	8 hr		Should be at full mark on oil indicator
Unit	Inspect	8 hr		Operator maintenance schedule
Water level (heat exchanger models)	Check	8 hr
Crankcase oil	Change	100 hr		First service — after first 50 hours of operation; drain while engine is still hot
Crankcase oil	Drain	50 hr		First service — Drain initial oil after 50 hours while engine is still hot
Cylinder head bolts and valve clearance	Adjust	50 hr		First service — after first 50 hours on an overhauled engine
Governor linkage	Clean	100 hr		Perform more often in extremely dirty conditions; lubricate old style linkage
Water filter	Check	100 hr		check after every 100 hours; change sooner in dirty water
Battery	Check	200 hr		Keep electrolyte level above plates
Brushes	Check	200 hr		Replace collector ring brushes when worn to 5/16 in; commutator brushes when worn to 5/8 in
Commutator	Check	200 hr
Fuel system condensation traps	Drain	200 hr
Oil filter	Replace	200 hr		every 200 hours of normal operation
Slip rings	Check	200 hr		Critical maintenance schedule
Crankcase breather pipe	Clean	500 hr		MDJC, MDJF Begin Spec T
Generator	Clean	500 hr
Rocker box oil line holes	Clean	500 hr
Valve clearance	Check	500 hr
Water pump (leaks and wear)	Inspect	500 hr		Replace if necessary
Primary fuel filter	Change	600 hr
Secondary fuel filter	Change	600 hr		Replace with every 5th change of the primary filter
Nozzle opening pressure and spray pattern	Test	1000 hr		Must be conducted by trained diesel injection equipment personnel
Valves	Adjust	1000 hr		Grind valves if required
Breather pulsation dampener element	Replace	2000 hr
Fuel filters	Change	2000 hr
Engine	Other	5000 hr		General overhaul if required
Valve stem tip-to-cap clearance	Check	5000 hr		or whenever parts exposed or removed
Cooling system	Clean		12 mo	clean and flush at least once a year
Heat exchanger sea water side	Clean		12 mo	yearly; remove end caps and flush tubes
Zinc pencil (heat exchanger)	Inspect		2 mo	Replace if deteriorated to less than 1/2 original size
Zinc pencils	Inspect		2 mo	replace if less than half original size

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

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Brush wear limit (replace)	5/8	in
Clearance	Camshaft bearing clearance limit	.0012-.0037	in
Clearance	Camshaft end play	0.007-0.039	in	room temperature
Clearance	Camshaft end play (in back position)	.007-.039	in
Clearance	Center main bearing clearance (4 cylinder)	0.0024-0.0052	in	original
Clearance	Clearance, large bearing to crankshaft	.001-.0033	in
Clearance	Collector ring run-out	0.002	in	compared to generator bearing
Clearance	Connecting rod bearing clearance	0.001-0.003	in
Clearance	Connecting rod large bearing diameter (I.D.)	2.0615-2.0630	in
Clearance	Connecting rod small bushing diameter (I.D.)	0.9903-0.9906	in
Clearance	Crankshaft connecting rod journal diameter	2.0597-2.0605	in
Clearance	Crankshaft end play	.010-.015	in
Clearance	Crankshaft end play	0.010-0.015	in	room temperature
Clearance	Crankshaft main bearing clearance (original equipment)	.0030-.0043	in
Clearance	Crankshaft main bearing journal diameter	2.2427-2.2435	in
Clearance	Cylinder diameter limits	3.4995-3.5005	in
Clearance	Exhaust valve clearance in guide	.0030-.0050	in
Clearance	Exhaust valve stem diameter	.3405-.3415	in
Clearance	Intake valve clearance in guide	.0015-.0030	in
Clearance	Intake valve stem diameter	.3405-.3410	in
Clearance	Main bearing clearance (1 & 2 cylinder)	0.0014-0.0052	in	replacement
Clearance	Main bearing clearance (1 & 2 cylinder)	0.002-0.0033	in	original
Clearance	Piston clearance in cylinder	0.005-0.007	in	90 degrees to pin, below oil ring
Clearance	Piston clearance to cylinder wall below oil ring groove	.0055-.0075	in	measure 90 degrees to pin
Clearance	Piston pin clearance	Thumb Push Fit
Clearance	Ring gap	0.010-0.020	in
Clearance	Starting motor armature end play	.005-.030	in
Clearance	Starting motor pinion clearance to pinion stop	.070-.120	in	solenoid plunger bottomed
Clearance	Starting motor pinion rest position (pinion housing mounting face to outer edge of pinion)	1-9/32 to 1-15/32	in
Clearance	Valve clearance	.020 (0.51), .018 (0.33), .011 (0.28), .016 (0.41), .017 (0.43), .017 (0.43)	inch (mm)	engine at room temperature about 70°F (21°C)
Clearance	Valve guide clearance exhaust	0.0030-0.0050	in
Clearance	Valve guide clearance intake	0.0015-0.003	in
Clearance	Valve stem tip-to-cap clearance	0.001-0.005	in
Gap	Breaker point gap (MAJ)	0.022	inch (0.56 mm)	full separation
Gap	Breaker point gap (MCCK)	0.020	inch (0.51 mm)
Gap	Centrifugal switch breaker points gap	.040	in
Gap	Centrifugal switch gap	0.020	in
Gap	Centrifugal switch gap	0.020 (0.51 mm)	in
Injection timing	Ignition timing (gasoline)	19	degrees BTC	1800 rpm or slower
Injection timing	Ignition timing (gasoline)	25	degrees BTC	3600 rpm or faster
Injection timing	Injection timing	17	degrees BTC
Injection timing	Injection timing	18	degrees BTC
Injection timing	Injection timing	19	degrees BTC	Later models after Spec P
Injection timing	Injection timing	21	degrees BTC	Before Spec P
Injection timing	PLB pump timing (DJA)	17	degrees BTC
Other	Battery charging high rate	6 to 8	amps
Other	Battery charging low rate	2 to 3	amps
Other	Battery charging rate solid state combined	5.26	amps
Other	Battery charging rate solid state high	3.7	amps
Other	Battery charging rate solid state low	1.56	amps
Other	Bilge blower time delay	5	minutes
Other	Cooling water flow	6	gallons per minute	after thermostat opens
Other	Cranking limiter time	45 to 90	seconds
Other	Cylinder bore	3-1/2	in
Other	Emergency relay K14 operation time	15	seconds
Other	Emergency time delay low oil shutdown	45	seconds
Other	Exhaust valve face seat angle	45	degrees
Other	Intake valve face seat angle	42	degrees
Other	Maximum operation angle MCCK, MDJA, MDJE	20	degrees	any direction
Other	Maximum operation angle MDJC, MDJF	30	degrees	any direction

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

Recommended fluids

Fluid	Grade	Standard	Ambient	Capacity	Notes
Coolant	50/50 mixture antifreeze and clean water				increase antifreeze percentage in extremely low temperatures (-25F or lower)
Coolant	Clean, alkali-free water	Add an approved rust inhibitor; anti-freeze if freezing			Closed cooling (heat exchanger) system
Coolant	antifreeze				Replace annually in captive system
Engine oil	5W-30	API CC/SE	below 0°C		recommended for service in ambient temperatures of 32F and colder
Engine oil	API CD/SE				Diesel engines; use CC/SE for first fill only (50 hours)
Engine oil	API SE or SE/CC				Gasoline engines
Engine oil	CC (formerly DM)	Passing MS Sequence Tests			First fill only (50 to 100 hours) for new or rebuilt J series diesel
Engine oil	SAE 10W-30, 5W-20, or 10W, 5W-30	API CD/SE or CD/SD			0 deg F to 32 deg F
Engine oil	SAE 30	API CD/SE or CD/SD (Series 3 Test; MS Sequences IIA and IIIA)		6.0 U.S. quarts	Above 32 deg F; do not mix brands or grades; plus 1/2 quart for new filter
Engine oil	SAE 5W-20 or 5W-30	API CD/SE or CD/SD			Third temperature row (label not legible in source)
Engine oil	SAE 15W-40 or 20W-40	API CD/SE or CC/SE	-10°C to 32°C		SAE 15W-40 or 20W-40 in 15F (-10C) through 90F (32C); multi-grade 5W-30 below 32F (0C)
Fuel	ASTM 2-D or 1-D	minimum Cetane number 45			use 1-D below 32F, long periods of light load or no load; low sulfur; pour point at least 10F below lowest expected
Fuel	No. 1 diesel	Low sulfur content; pour point at least 10 deg F below lowest expected temperature			When ambient temperature is below 32 deg F, or at all temperatures during long periods of light engine load
Fuel	No. 2 diesel				Best economy
Fuel	nonleaded gasoline				Recommended for gasoline engines
Grease	graphite lubricant				Steel governor ball joints

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

Procedures

Adjust Carburetor adjustment

⚠ Do not force needles against seats.

Open both needles 1 to 1-1/2 turns off seats.
Apply full load; turn main fuel screw in until speed drops, then out to normal.
Remove load; turn idle screw out until speed drops, then in to normal.

Adjust Governor Linkage (Diesel) adjustment

Loosen locknuts on governor linkage, remove link at one ball joint.
Position governor arm and fuel control arm fully forward.
Adjust linkage so both ball joints fit without moving arms.
Tighten locknuts.
Release fuel solenoid plunger.

Adjust Valve Clearance (Diesel) adjustment

Tools: feeler gauge, socket wrench

Turn flywheel to compression stroke for cylinder to adjust.
Turn flywheel clockwise additional 10 to 45 degrees.
Loosen locknut to increase clearance, tighten to reduce.
Use feeler gauge to set proper gap.
Adjust in firing order 1-2-4-3.

Adjust Valve Tappet (Gasoline) adjustment

Tools: feeler gauge, wrench

Remove valve covers.
Crank engine until intake valve opens and closes.
Continue 1/4 turn until timing marks align.
Turn adjusting screw to obtain correct clearance.
Use flat feeler gauge between valve and valve rotator.

Battery Charge Rate Adjustment adjustment

⚠ Avoid overcharging.

Tools: DC ammeter

Set slide tap on resistor R4 to about 2 amperes charging rate.
For frequent starts, increase charge rate slightly until battery stays charged.
Stop engine when readjusting to avoid shorts.

Checking Centrifugal Breaker Points adjustment

Tools: Thickness gauge, Socket wrench, File or fine stone

Rotate engine crankshaft a few degrees counterclockwise before adjusting points (use socket wrench on flywheel retaining screw).
Measure gap with a thickness gauge; set gap at .040 in.
Loosen and move the stationary contact to correct gap.
Dress slightly burned points smooth with a file or fine stone; replace burned or faulty points.

Checking and Adjusting Valve Clearance adjustment

Tools: Feeler gauge, Socket wrench

Turn flywheel until cylinder to be adjusted is on compression stroke (socket wrench on flywheel screw hex head).
Turn flywheel clockwise an additional 10 to 45 degrees so piston is on power stroke with both valves closed.
Loosen the rocker arm locknut to increase clearance; tighten to reduce clearance.
Using a feeler gauge, check clearance between rocker arm and valve; set to .017 in intake and .017 in exhaust.
Always adjust valve clearances in the firing order (1-2-4-3) sequence, rotating flywheel 180 degrees between cylinders.

Fuel Injection Pump Timing (MDJA Method 2) adjustment

Install pump with 0.006-inch (0.15 mm) shims.
Loosen delivery valve holder to relieve spring pressure.
Rotate flywheel to about 15 degrees before port closing point.
Blow in pump inlet and rotate flywheel slowly clockwise until air stops.
Measure distance from port closing point to PC mark.
Select shims from table and install pump.

Governor Sensitivity Adjustment adjustment

⚠ If the governor is too sensitive, a rapid hunting condition occurs.

Turn the sensitivity adjusting ratchet counterclockwise for more sensitivity (less speed drop at full load).
Turn clockwise for less sensitivity (more speed drop).
Adjust for maximum sensitivity without hunting.
Readjust speed after sensitivity adjustment.
Secure the lock nut.

Governor Speed Adjustment adjustment

⚠ Excessive droop may be caused by engine misfiring; correct this before adjusting the governor.

Tools: Tachometer or frequency meter

Change spring tension by turning the governor spring nut.
Turn nut clockwise (more spring tension) to increase RPM.
Turn nut counterclockwise to reduce governed speed.
Hold a tachometer against the flywheel cap screw or use a frequency meter.
After adjusting, secure the lock nut.

Set Breaker Points (MAJ) adjustment

Remove flywheel and examine breaker points.
Adjust gap to .022 inch (0.56 mm) at full separation.
Loosen screw to shift point set, retighten securely.

Time Ignition (MCCK) adjustment

Tools: continuity light, thickness gauge

Crank engine to fully open breaker points.
Loosen locking screws and turn cam to adjust.
Set point gap to .020 inch (0.51 mm).
Shift breaker point box to align timing mark.

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	Leads	Notes
		12-lead broad range reconnectible alternator	12 lead	User connects for required voltage and amperage
		X1 to VR21-5	X1	for 50 Hertz
		X1 to VR21-6	X1	for 60 Hertz
120	1	2-wire		Reconnectible
120/240	1	3-wire		Standard connection for MCCK/MDJE/MDJC/MDJF
240	1	2-wire		Reconnectible

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 MDJF?

The Cummins/Onan MDJF engine has an oil capacity of 6.2 liters.

What is the displacement of the Cummins/Onan MDJF?

The Cummins/Onan MDJF has a displacement of 2.3 liters.

Which generators use the Cummins/Onan MDJF engine?

The Cummins/Onan MDJF powers 2 generator set(s), including Cummins/Onan 15.0MDJF, Cummins/Onan 15.0MDJF-3CR.

What is a common problem with the Cummins/Onan MDJF engine?

A commonly reported issue on generators using the Cummins/Onan MDJF is: Water or foreign material in the fuel can ruin the injection system.. Cause: If daily inspection shows water or dirt in the fuel pump sediment bowl. Fix: Fuel handling and storage facilities should be checked and situation corrected. Fi Iter elements should be replaced following corrections of fuel contamination problems..