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Old 06-25-2011, 07:23 PM   #15
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If we were closer to home I'd meet you on one of our Costco/Home Depot runs to try and figure this out.
It sounds like your transfer switch is not kicking in so no 120 vac to the coach. That may be because your gen. is not running long enough to engage the transfer switch or the transfer switch is engaging, loading the gen. and shutting it down. The fact that your unit runs w/o recognizing oil pressure is fascinating as is the fact that it seems it is looking for output load to stay running and the BF is pre CPU days.
I worked for Onan many years ago when they were in New Brighten, MN. and have some friends from there. They may offer me some advice.
Sorry I can't be more help but I'll keep digging.
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Old 06-25-2011, 10:54 PM   #16
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1. Fuel pump pressure should only be 2 1/2 to 3 1/2 lbs. Higher pressures can force the inlet needle off of the seat and cause the carburator to flood.

2. The bi-metal strip in the choke is temperature sensitive. Typically closed at 58 degrees and opened by 82 degrees. The voltage (approx 12VDC) to the coil heats it up and opens the choke. A choke set to lean can result in the engine shutting down before it warms up. A choke set to rich will cause the engine sputter and you may see black smoke out the exhaust after a few minutes of running. If there is no voltage to the choke or if it is open then the choke is not being disengaged (choke always on).

3. The oil pressure switch grounds out the points if there is low oil pressure. By disconnecting the lead to it, you eliminate that safety feature. Disconnecting the wire is one of the troubleshooting steps when trying to isolate a no start condition. Given that your unit still shuts down after 15 secounds with the wire disconnected proves the oil presure switch is not your problem.

4. Another safety feature that was used on SPEC B versions is overtemp shut down. Like the oil pressure switch, it grounds out the points if the temperature gets to hot. It may be weak and shutting the unit down incorrectly. If installed it can be disconnected in the same manner as the oil pressure switch.

5. All that information is from the Onan 900-0337 service manual. It describes BF (Spec A/B) operation and troubleshooting.

Dave
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Old 06-26-2011, 10:25 AM   #17
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The fuel pump may be too much, but I don't think flooding is the problem with the shutdown due to the fact that it starts right back up each time.

Dave, you mentioned an overtemp shutdown. Does your service manual mention where it would be if it has one? (with my luck it would be on the back side somewhere)

bigskymt....I am very familiar with the Costco/Home Depot runs as we just made one last night!
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Old 06-26-2011, 12:39 PM   #18
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It is shown as an option on the SPEC B wiring diagram but I was not able to locate it in the parts book (965-0220) or supplemental parts book (965-2501). Another potential item would be if a fuel shut off valve is also installed. Refered to in the operators manual (965-0120) for later model motorhomes with (75 up?) with evaporative control emmission requirements. Taps off fuel pump lead.
When the engine is running and you let go of the start switch the K1/K2 relays de-energize and DC run voltage is supplied by the DC portion portion of the generator. The generator DC portion can cause your problem also (DC voltage failure) becasue it supplies the run votage.
During start, K1 provides B+ to the generator to use it as a starter. The K2 relay supplies B+ (via F2) to the coil (+ terminal), Fuel pump, Fuel shut off solinoid (if installed), and noise reducing capacitor C1.
The points/condensor, oil pressure switch, and thermal switch (if installed) are connected to the coil (-) terminal. Both the oil pressure and thermal switch would ground the coil (-) terminal shorting out the points for safety shutdown. The STOP position of the Start/Stop does the same thing (ground coil [-]).
I am sending a private message to you for the manuals. Check your IVR2 private mail. Everything I am telling you came from the manuals.

BTW some of the older generators like this one occasionally required the fields to be flashed.
http://www.perr.com/tip16.html

Dave
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Old 06-26-2011, 01:30 PM   #19
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My schematics that are supposed to cover the older pre-CPU gen. do not show the oil pressure switch tied to the points or even a thermo switch.
Based on your results I would have to conclude my diagrams are incorrect for your model.
Sorry for the incorrect information.
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Old 06-26-2011, 02:15 PM   #20
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Have you tried disconnecting the coach from shore power BEFORE trying to start the gen set? Automatic Transfer Switch might be overriding the gen set.
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Old 06-26-2011, 02:28 PM   #21
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Here is the BF schematic from 900-0337.
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Old 06-26-2011, 11:55 PM   #22
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Quote:
Originally Posted by Dave78Chief View Post
It is shown as an option on the SPEC B wiring diagram but I was not able to locate it in the parts book (965-0220) or supplemental parts book (965-2501). Another potential item would be if a fuel shut off valve is also installed. Refered to in the operators manual (965-0120) for later model motorhomes with (75 up?) with evaporative control emmission requirements. Taps off fuel pump lead.
When the engine is running and you let go of the start switch the K1/K2 relays de-energize and DC run voltage is supplied by the DC portion portion of the generator. The generator DC portion can cause your problem also (DC voltage failure) becasue it supplies the run votage.
During start, K1 provides B+ to the generator to use it as a starter. The K2 relay supplies B+ (via F2) to the coil (+ terminal), Fuel pump, Fuel shut off solinoid (if installed), and noise reducing capacitor C1.
The points/condensor, oil pressure switch, and thermal switch (if installed) are connected to the coil (-) terminal. Both the oil pressure and thermal switch would ground the coil (-) terminal shorting out the points for safety shutdown. The STOP position of the Start/Stop does the same thing (ground coil [-]).
I am sending a private message to you for the manuals. Check your IVR2 private mail. Everything I am telling you came from the manuals.

BTW some of the older generators like this one occasionally required the fields to be flashed.
PER Notebook - Generator Field Flashing

Dave

My unit doesn't appear to have the thermal switch. I can account for all the wires coming from the coil except for a condenser looking thing mounted next to the coil. It's a small 2" long by 1/2" diameter cylinder. (I'm guessing that could be the C1 noise reducing capacitor)

Dave, thank you for directing me to the service manual. I'm not real good with electrical schematics, but it appears that I've checked and re-checked everything that I have read about and that you-all have mentioned. Obviously there is something that I am missing.

I really think that it is spark related rather than fuel. I've even tried pouring a small amount of gas directly in the carb as it is shutting down which did not make it pick back up.

I'm to the point now where I'm ready to give my brain a rest for a while unless anyone thinks of something else to check.

I really appreciate these forums and all of you that are willing to lend your expertise to us DIYers that really don't know what we are doing.

I'm not signing off, just losing patience with this thing!

Jeremy
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Old 06-28-2011, 01:58 AM   #23
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I worked on a older Onan that had a "Run" relay that kicked in after a few seconds. The relay operated, but the contacts didn't make. A simple adjustment of the contact fixed it.
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Old 06-28-2011, 10:32 PM   #24
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Tonight I removed the fuel shutoff solenoid to see if it was causing anything...no change.

I was running it again a few minutes ago and when it shut down, I pressed the start button before it came to a stop and it will fire right back up. I did this over and over and over again for 5-10 minutes. It's almost like something is shutting down the electrical and when I press the start button again, it takes off...for another 15 seconds or so.
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Old 06-28-2011, 11:19 PM   #25
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If it has the timer circuit like the one I worked on, the relay might not be making contact, if and when it pulls up. Can you hear anything click right before it dies?
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Old 06-29-2011, 06:35 PM   #26
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Your description indicates an electrical problem.
Looking at the schematic:
Both the K1 and K2 relays are used to start the generator. Both are de-energized when you let go of the start switch.
The K1 relay provides the voltage for the generator to perform as a starter. On the drawing the K1 contacts are located just to the right and below the CR1 diode (left side of drawing). When you let go of the start switch the K1 relay de-energizes removing starter voltage. From your description the K1 relay is doing everything it is supposed to.
The K2 relay provides the voltage to the ignition and fuel circuits for starting. The K2 contacts are just to the left of fuse F2. When you let go of the start switch the K2 relay de-energizes removing ignition voltage "from the battery". When you keep hitting the start switch you are energizing the K2 relay which provides the ignition voltage again. What is supposed to happen is during the start phase (start switch depressed) the generators alternator is supposed to begin generating voltage and suppling that voltage to the ignition circuit via R1 and to the F2 fuse. When you let go of the start switch voltage is suppsed to continue to be supplied via R1 and F2 to the coil to keep it running. You are losing the run voltage from R1. It could be a bad connection, worn brushes or armarture/coil problem. Your description points to the generators alternator section.
For reference (not related to your problem),
A) When you depress the stop switch, it grounds out the ignition coil so the engine stops. The CR1 path provides the voltage to recharge the battery.
B) F1 is only a B+ supply protection fuse for the remote starting panel. F1 is not used if you do not have a remote panel.

Troubleshooting procedures for the alternator section are in the manuals that I sent you the links for.

Dave
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Old 12-06-2011, 06:52 PM   #27
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Did you ever figuer out what the issue was with your gen set? I would like to know how you made out.
Thanks
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