Onan 6KW Generator Repair
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The 1975 GMC Palm Beach has an Onan 6000 Watt Generator installed in a slide out tray on the left rear of the coach called a Power Drawer.
First I would like to thank Duane Simmons for all his help and the schematics with trouble shooting the problems with the generator.
(See the end of the article for images of my Onan 6KW Generator efforts).
When I bought the coach (I really didn't know that much about the AC electrical system in a motor home) the people that maintained the coach for the owner (who came to the South West in the winter from New Jersey) had 'hot wired' the ignition system of the generator engine. This is a bad practice on the part of the mechanics, by passing the controller on the generator/engine could result in a fire.
Once I figured out what was done to the engine I set out rectify the problem by rewiring the controller and associated wire harness.
When I started I contacted Mr. Duane Simmons, he repairs controller boards. He told me that there were three bad parts on the board and it cost me $106 plus the shipping to get the board to him. He has a nice checklist he sends to run down your major problem with the engine but with all the problems the controller board had it was useless to me.
When I received the controller board back I put it on the generator and connected all the wires. The engine would still not start. After talking to Mr. Simmons I went back to tracing wires. The wiring harness had three wires that were cut at the connector between the J1 harness and the J2 harness.
Now comes the problem with all the documentation that I have gathered about the Onan 6KW Generator /. Power Drawer series generators. The schematics and the illustrations are incomplete in that if you want to find the 'Voltage Regulator' it is not noted in any of the manuals I have. There is a 'Regulator' in the Illustrated Parts book on page 28-74 Item # 32.
Another problem I have encountered is that the Onan 6KW Generator wiring diagrams I have ( four different ones) have different numbers for the wires. Such as on three diagrams the # 1 wire in the harness is the Ground, one shows it as # 6. With three wires cut it is hard to figure out which wires are missing because none of the illustrations I have show the wires connected to physical components. Now this would be ok for a tech that was factory trained or the lucky guy that had another complete generator to compare the wiring against.
Here is what I did:
After trying a new wiring harness from Cinnabar for over a hundred dollars (which is not even close to the original harness, I think it is for a different Onan Generator that doesn't use the split harness) so I returned it.
I tried to rebuild the original harness but with the three cut wires and not having the location of where those three wires connected physically I was at a stand still for almost nine months.
One day I was searching for some replacement parts for the interior of the coach when I stumbled across a web site here in Phoenix that has Onan Generators!
I called the owner (Ed) of the recycle yard and yes they do have an Onan 6KW Generator. After looking at the generator, and talking to Ed, we made a deal that I would give him $500 plus $250 to check out the generator and then remove the one in the coach and put the replacement generator in the coach, he keeps the old one. Cool.
Unfortunately the tech that works for him didn't want or think that the amount of money we agreed on was sufficient to do the job. After waiting three weeks I talked to the owner about buying the Onan 6KW Generator and having the generator delivered to my home for the price of $500 cash.
This generator is not from the desert South West. How do I know that? The wiring is still supple, not dried out and cracked!
Before doing anything the first thing I did was a little cleaning. Then I numbered all the wires on the controller side of the wiring harness and took a lot of pictures.
Because the documentation does not tell you that the Alternator is behind the fan and that the hot wire from the alternator goes from behind the fan, down past the starter then up beside the controller board, then across the top of the generator to the left side of the chassis to the 'Voltage Regulator' I would have never found that wire on the old generator, it is one of the cut wires! That is one of the reasons the controller board was by passed and the engine was hot wired. (The cut wires were J2-8, J2-6, and the alternator wire).
Because I didn't have a way to secure the second generator, I did not try to start it, I was considering swapping the second generator for the one in the coach but I know nothing about the one I bought even though it looks fairly new or has low hours. The oil looks fairly new and clean. But knowing the generator in the coach will run if hot wired I deiced to not start the second generator.
After taking a lot of pictures of the second generator and making drawings of where the location of the wires of the harness were connected physically. I labeled wires and the pictures I had taken. I pulled the harness off the second generator.
I then pulled the harness off the coach generator and did a compare to the harness from the second generator. It was pretty close with the exception of one wire that was on the starter solenoid Pin # 11 and connector # 11 on controller board, it was on the second small post vs the starter side large post so I left that one as it was and finished putting the harness on the coach generator.
I left the remote start wires disconnected and used Mr Simmons's check list to check the voltages, now this is the second generator controller board, the board failed two of the steps but the starter does engage.
Then I put the controller Mr Simmons rebuilt on the coach generator and tried again, it cranks but will not start.
When I checked the voltage to the points I noticed that it always had power, looking at the wire from the points to the coil I see the installation has degraded and is bare in spots, although it wasn't shorting out against the generator. So I removed the points assembly from the second generator and the coach generator and did a comparison on the physical characteristics. They match and the wire on the second generator points is in a lot better shape so I installed the second generator points assembly on the coach generator.
Then I tried to start it coach generator again, it choughs but won't start. That was when I noticed that the carburetor on the coach generator was leaking gas. Not a good thing - leaking gas. So I looked at the second generator carburetor and decide if I cleaned it up it may not need to be rebuilt at this time. After using a can of carb cleaner and then blowing the cleaner out with my compressor, I installed it on the coach generator.
Using a jumper wire from the positive post on the battery to the fuel pump I let it build up pressure and looked for leaks, no leaks!
So I crank it up, it starts!
Remembering that a generator that has not been run in some time needs to run for at least three minutes before loading it up, I let the coach generator run for fifteen minutes. Then I shut it down for half an hour.
The next time I started the coach generator I let it run for three minutes before I went in the coach and started testing all the lights and outlets with a drop light. I have AC power!
After the those tests (about ten minutes) I turned on the rear A/C, it runs and cools the Coach! Then after about a half hour I turned on the front A/C. When the front A/C compressor engaged the generator tripped off line. It was late in the evening so I just shut everything down until the next day.
The next day I started the generator up (cranked on the second try with out jumping the fuel pump!) let it run for three minutes then turned on the rear A/C and set it for low cool, let that one run for ten minutes then turned on the front A/C and set it for low cool also. After about three minutes the front A/C compressor came on but the generator did not trip off line.
Now the coach has electricity and both A/C's work!
Next is the refrigerator, once I get the seals cleaned up and the interior/exterior cleaned up I will check that, then the hot water heater and the pumps.
Images of the generator:
The yellow arrows show an item of interest, if numbered then there are more than one item that requires explanation.
Under the right (#1) cylinder head and below the oil filter are four wires, tied in two bundles. The # 1 bundle are the oil pressure and the choke connections. The #2 bundle are the alternator wires, one goes to the starter solenoid the other goes across the top of the generator to the Voltage Regulator (VR).
The Onan 6KW Generator Voltage Regulator
The # 1 wire is the hot wire from the Alternator along with the J2-8 Pin #8 on controller board from the controller board. The #2 is the J2-6 Pin #5 on the controller board. # 3 is an empty connection post.
The lower arrow points to the fuel pressure switch, the upper arrow points to the ground for the fuel pressure switch. (Removed on coach generator).
The left arrow points at the # 1 spark plug. The right arrow points to the positive terminal of the coil.
Note the jack on the right, I used it to lift and roll the Onan 6KW Generator out on the rails because the other side is coved by a large plate.
The arrow points to the wiring that comes down between the splash plate and the # 1 cylinder head. To the right is a 1/4" steal plate, when the generator is all the way in the drawer it covers this side of the generator, the hole in the plate matches the oil filter.
The positive cable for the Onan 6KW Generator starter.
The top arrow is the wire bundle that goes across the top of the generator, in that bundle is one of the Alternator connections (which was cut on the coach Onan 6KW Generator). The lower arrow points to the wire bundle from the Alternator with the oil pressure switch and choke connections.
Arrow # 1 is the alternator connection and the J2-8 connector, # 2 is the connection J2-6 , #3 is an open connector that is connected to same post as the # 2 connection.
At the top #1 is the two wires for the alternator, at the bottom are the two wires for the oil pressure and the choke.
Another shot of the four wires that goes through the Onan 6KW Generator splash shield.
The Onan 6KW Generator all the way out of the drawer.
Reset for the Onan 6KW Generator AC circuit breaker.
The controller board, the installation on the wires is soft and supple, almost like brand new. Except where the wires were painted you can see the markings for the wire quite well. This helped a lot with identifying where each wire went.
# 1 is the starter solenoid post that didn't have a connection on the second generator(J2-11). # 2 is the post on the coach generator that has a wire from the controller board J2-11 that I left alone .
Another view of the Onan 6KW Generator starter solenoid.
Inside the fan shroud with the fan is the alternator, # 1 shows the wire bundle and insulating cover. # 2 is the alternator itself.
Controller board, beside each connector pin is the actual pin number that corresponds with the J1 connector wires. This came from a manual Michael from Texas sent me for the Onan 6KW Power Drawer because he is closing down his Salvage Yard.
As you can see this generator did not have a lot of hours or was well taken care of by the owner, also I don't believe that this generator spent much time in the desert southwest because the wiring is in excellent shape. Where as the wiring on the coach generator the insulation is hard and is cracking, see my comments about the points.
A Junk Yard Gem for sure, so look around, you never know what you will find. :)
After a year and a half of messing around with the original Onan 6KW Generator I decided to change it out for the one I bought at the junk yard, click here for the steps I took including cleaning the generator bay and re-insulating it.
There is a nice pdf for the Onan 6KW Generator at www.bdub.net you can download it there for free.
These images were extracted from the manual at bdub.net (link above) to help you with your generator:
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Onan 6KW Generator Repair