I have been working on my onan 4000 generator for a while, checking all the common fixes to no avail. the shop foreman at cummins told me it probably is the AC kickback. he hinted there was a way to bypass it but of course would not tell me. does anybody know of this and how can you do it?
onan 4000 generator fix?
- Thread starter pghwayne
- Start date
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catblaster
Well-known member
buchanan said:
Has something to do with relays not being able to handle inductive loads but no idea how the term is being used in this case. Sound like double speak.
it starts and quits immediately. checked all the common issues. spark, fuel flow sensor on carb, cleaned all electrical connections. used starting fluid and started and quit, even tried another quick shot to keep it running.but died immediately.stumped
pghwayne said:
have u tried taking off a plug wire and short it to plug via screw driver and watch if it has full spark even when it dies?
also I wonder if this AC
deal is where the ac relay is stuck on so as soon as the engine fires its trys to produce 120V so instantaneously stalls the engine?
catblaster
Well-known member
Pasted this from flight systems troubleshooting guide, sorry if this is not allowed. With all your checking have you tried the oil pressure sending unit (if it has one). Even if it has oil, if it doesnt get the signal it wont keep running.
Normal Starting Sequence
This is what normally happens when you start your genset. Pressing and holding the start switch causes the control
board to send 12 volts to the ignition, fuel pump, choke heater, start solenoid and field flash circuits. The engine then
cranks and starts. Oil pressure and generator voltage build up within 1-2 seconds. This causes the control board to
keep sending 12 volts to the ignition, fuel pump and choke heater while cutting off 12 volts to the starter solenoid and
field flash circuits. The start switch can then be released and the engine keeps running. Some models differ slightly in
operation. On models equipped with magneto ignition (KV, Spec. C-F; KY, Spec. A-E), the control board un-grounds
the magneto kill circuit. Model KY, Spec. B-E uses a fuel solenoid in addition to the fuel pump. Models fueled by LP
gas use a fuel shutoff solenoid valve instead of a fuel pump. Several conditions can prevent the engine from starting/
running and are covered under Troubleshooting.
Normal Starting Sequence
This is what normally happens when you start your genset. Pressing and holding the start switch causes the control
board to send 12 volts to the ignition, fuel pump, choke heater, start solenoid and field flash circuits. The engine then
cranks and starts. Oil pressure and generator voltage build up within 1-2 seconds. This causes the control board to
keep sending 12 volts to the ignition, fuel pump and choke heater while cutting off 12 volts to the starter solenoid and
field flash circuits. The start switch can then be released and the engine keeps running. Some models differ slightly in
operation. On models equipped with magneto ignition (KV, Spec. C-F; KY, Spec. A-E), the control board un-grounds
the magneto kill circuit. Model KY, Spec. B-E uses a fuel solenoid in addition to the fuel pump. Models fueled by LP
gas use a fuel shutoff solenoid valve instead of a fuel pump. Several conditions can prevent the engine from starting/
running and are covered under Troubleshooting.
boatbuilder
Well-known member
If it is an older unit I would check the oil pressure switch. Over time the diaphragm will develop a pin hole which keeps it from opening or closing depending on the ignition system.
The switch is located under the oil filter behind a tin plate on your model I believe but if you google Onan troubleshooting flight systems the entire manual comes up with charts and pin locations etc. Just click the link and download the PDF and you will have it for the future. Here it is. http://www.flightsystems.com/pdf/onan-rv-troubleshooing-guide.pdf
boatbuilder
Well-known member
Losing the spark is a sign that the ignition is shutting down. There should be a single wire on the oil pressure switch that can be unhooked and taped over. After that try to start the genset again. If it keeps running you have found the issue.
Lou Schneider
Site Team
- Joined
- Mar 14, 2005
- Posts
- 13,250
The control board has to see oil pressure via the oil pressure sensor and voltage from the generator to keep running after you release the start switch. The voltage problem could be something as simple as dirty slip rings that keep the excitation voltage from reaching the armature to other problems in the control board.
The easy way to check if the generator is shutting down from a low oil pressure signal is to just remove the wire running to the pressure switch. It grounds the circuit if it thinks oil pressure is low.
The easy way to check if the generator is shutting down from a low oil pressure signal is to just remove the wire running to the pressure switch. It grounds the circuit if it thinks oil pressure is low.
Gary RV_Wizard
Site Team
As long as you hold the starter switch down, the controller sends 12v power to the necessary places (fuel pump, start motor, etc) and overrides the normal interlocks such as low oil pressure. As soon as you release the switch, the interlocks become active and the generator is expected to operate on its own, powering the pump, making spark, etc. It sounds like yours is entering the shutdown mode when you release the start switch, so one of the "run" conditions is not being met.
pghwayne said:
Iam not 100% sure but would assume so .I don't think the oil switch is the problem but if it is I would be bypassing that deal
I know the Controll boards were a major problem for a few years on older onans so that's why I tend to say control board
One more thing when u try and start it fires up and dies and if u keep cranking it is a no run and no spark situation(correct)
How long do u have to let it sit before this will repeat? or will it repeat as soon as u let off the start and retry system
Can u get a meter on the 120V output wire and see if there is voltage for a short time while it does its run burst?
some onan,s will run while not producing 120V but not many
The BGM /NHM Marquis, spec B onwards, is one of the few Onan rv gensets
that WILL run without producing output - this is because, as an
electronically governed set, it uses a signal from the governor to tell that
the genset is running, rather than the presence of output from the set.
Alfa38User
Well-known member
- Joined
- Oct 4, 2007
- Posts
- 6,678
I would be surprised if the oil pressure switch is actually in the pan. There is not a lot of pressure there...imho. And no, if it is really there, there would not be a wire, no way to get the wire or any reading out. Oil level maybe??... No Oil Filter ? hmmm. I guess we need to know exactly which model this Onan is....
