Sign in to follow this  

1984 Onan 4.0b Genarator

Recommended Posts


I am a new rv owner and like what I see on your forum.Good stuff.

I have a 84 26' Southwind motorhome.

The question,the generator stopped running(no spark). Ran fine and the next time would not start,cranked and have gas

The points are making and braking,i have 12 volts to the coil but no spark. I have read if there is nothing coming from the gen or no oil psi that will not start.

The only problem I see is the slip rings are black and i will measure but bet the brushes are worn.

Is there a way to clean the rings in the chassis? I will replace the brushes but make no sense to do so if the rings are less then clean.

The unit has 800 hours on it.

Even if the out put is not the problem they still need to be serviced..

I was a power boat tech for 24 years so I am familiar with most of the systems.

Thank you for any help.

Share this post

Link to post
Share on other sites


Welcome to the FMCA forum!

From your post it sounds like you do not have spark at this time. The engine is cranking with fuel and oil.

Points are set.

Check the ignition coil, also check to make sure there is no short between the points to ground. You should have 12 volts between them and ground.

Check both ends of the coil wire for good / clean connections.

Let the group know what you find.

Regarding the armature cleaning, that can be tricky; depends on how much room you have as it is a tight space to work in when the generators are mounted.


Share this post

Link to post
Share on other sites

If there is no 120 ac output the engine will still crank, but will go dead when you release the start switch, oil low will not even try to crank, and I'm reasonably sure that you have checked that.

Rich has good suggestions, hope this tidbit is helpful.


Share this post

Link to post
Share on other sites


Welcome to the Forum.

Your Generator (4.0 kw) is a splash lube unit. If your unit will turn over but not start, you may be low on oil. There is a low oil sensor which will not allow the unit to start. So check your oil.

Also how is the fuel level in the coaches tank. When the fuel tanks is below 1/4 the generator pickup tube will be above the fuel level.

Do you have 12 v to the coil? When all else fails take hold of the coil wire and have the DW try to start to unit. If the coil is good, it wont take long to find out. :lol: :lol:

Side note, the unit will run even if the ring is black and the brushes are worn.


Share this post

Link to post
Share on other sites


Could you post the model of your generator ? The information is for a Model BGE Onan built around 1984-86 time period.

So ignition information should be close.

The FMCA web page is going through some updating starting tomorrow, for about 10 days.This may cause some problems accessing the forum.

Hope the fallowing information helps you get it running.

Note, the relays used in these units where sealed and filled with Nitrogen to extend life of the relays



Ignition system wiring includes: (1) One positive (B+)

wire which carries the low voltage current from the

battery to the primary winding of the coil. (2) One

negative (-) wire which carries low voltage to the

points and condenser. (3) Two high tension wires

that carry the high voltage current from the secondary

winding of the coil to the spark plugs. The spark

plugs and coil secondary are all.grounded to the

engine making a complete circuit for the voltage back

to the battery. The ignition coil primary (low voltage

side) is grounded when the breaker points close.

Check all low voltage wiring for loose connections

and cuts or breaks in the insulation. Clean all terminals

and connections and test for continuity with an

ohmmeter. Use a megger to check for breaks in the

spark plug wire insulation.

Printed Circuit Board Assembly

The printed circuit board assembly is the center of

the generator set control system. The PC board circuitry

controls the start, starter disconnection, stop,

and battery charging functions. The primary components

of the PC board include three relays, one power

rectifier, two diodes, one capacitor, five resistors, and

a 5-ampere fuse. The only serviceable

component is the fuse which is removable from the

front of the control panel. connections to the PC

board are made through an eight pin connector (Pl).

mounted on the board and through the six lead wiring

harness. The PC board assembly mounts on the back

of the control panel.

Starting .

Placing the Start/Run/Stop switch in the Start position

connects battery ground (B-) to the K4 start

relay. This energizes the K4 relay which closes two

sets of contacts (K4-2,8 and K4-9,15) that connect

battery positive (B+) to the generator field windings

through (CR4 +), T1 Ignition coil, E3 fuel pump, and

K1 start solenoid. Connecting B+ as deschbed produces

the following control responses:

Flashes the field to ensure there is adequate residual

magnetism to induce voltage buildup.

0 Energizes the ignition coil (Tl) so it can begin producing

an ignition spark when the breaker points

begin to open and close.

0 Energizes the fuel pump (E3) which begins pumping

fuel to the carburetor.

0 Energizes the K1 start solenoid to close the K1


Closing the K1 start solenoid contacts connects B+ to

the starter motor. This energizes the starter motor

which begins to crank the engine to initiate starting.

Starter Lockout-Run

When the engine starts, the low oil pressure switch

(S2) closes to connect battery ground (B-) to the K3

run relay. As the engine comes up to speed, AC output

voltage from the generator is supplied to the choke

heater element (HI) and to the K2generator relay.This

activates the heating element (which opens the choke)

and also energizes the K2 relay. Energizing the K2

relay closes one set of contacts (K2-25) that connect

B+ to the K2 run relay. This energizes the K3 relay

which opens two sets of contacts to produce the following

control responses:

Closing the K3-9,15 contacts (which parallel the

K4-2,8 contacts) provides an alternate pathway for

supplying B+ to the T1 ignition coil and E3 fuel


Opening the K3-1,8 contacts disconnects B+ (CR4

positive terminal) from the generator field windings.

Closing the K3-2,8 contacts connects B+ to the run

light, time meter, and battery condition meter.

Opening the K3-9,16 contacts disconnects B+from

the K4 start relay causing it to DE-energize.

De-energizing the K4 relay opens the K4-2,8 and K4-

9,15 relay contacts. Opening the K4-2,8 contacts has

no effect since they are in parallel with the closed

K3-9,15 contacts which connect B+ to the ignition

coil and the fuel pump. Opening the K4-9,15 contacts

disconnects 6+ from the K1 start solenoid. De energizing

the K1 start solenoid disconnects B+ from

the starter motor which stops cranking.

When the S1 switch is placed in the RUN position, the

engine continues to run. Relays K2 (generator relay)

and K3 (run relay) are energized while relays K1 (start

solenoid) and K4 (start relay) are De-energized.

Generator voltage is rectified to DC by the CR-l power

rectifiers and supplied to the battery through the

charge resistor (R6). This charges the battery at a

constant rate (1 ampere maximum) during set


Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this