Onan 4000

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dktool

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Apr 3, 2015
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153
Thank you for the service manual link, I'll get to working on it very soon.

If the voltage regulator is dead anyone know a good replacement source ?
 

NY_Dutch

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Nov 22, 2010
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Where our wheels take us!
I was able to look at the slip rings, they are definitely tarnished.
I would like to check the resistance as is for a baseline reference before cleaning.

Is the rubber'ish pop in cover under / near the air filter cover meant to be an access point for cleaning or something else ?
The "rubberish" cover is for access to the brushes...

Oh, and for reference when looking up parts, your generator is a "Spec J".
 

dktool

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Apr 3, 2015
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Thanks for the info fellas !

Here's where I'm at;
I measured the brush / slip ring resistance at the rectangular connector (unplugged of course) using my semi vintage, never fail me Fluke 87, I got a consistent repeatable 24+-.4 ohms.
The rings are not shinny by any stretch but I have seen much worse in eddy motors and commutators.
So it would appear the field connection is sound.

Looks to me like the arrow is pointing at the regulator. I'm going to dig through the 161 page service manual and see if there's a ohm out test for it before declaring it deceased.

What say ye ?

Also, my regulator p/n is: 305-0752D
the circuit board is: 300-3763
 

Isaac-1

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Dec 3, 2016
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SW Louisiana
Sounds likely, there is probably a testing procedure in the manual to apply voltage to the exciter leads using a small 9v battery and then checking for AC output. though this depends on the exact generator design.
 

dktool

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Apr 3, 2015
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After further inspection my regulator has a flight system p/n label on it (which is correct for my unit) but the case has the 305-0752 D number.
I guess they use whatever gutted base they can find when the build theirs and don't remove the oem number. Which in this case is the wrong p/n for my unit.
 

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dktool

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On the subject of starting these generators under load, what is considered too heavy of a load ?
After all, each time they start and as soon as the output AC goes active the DC converter in the coach is already wired on.

I read that they need to run 30 seconds after AC output starts before applying any load.
?????
 

Mark_K5LXP

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Albuquerque, NM
It would be my guess that 30 seconds allows the engine to stabilize a bit before dumping a load on it, with the idea it might "wander" or surge a bit when started from cold. Thinking too it's probably more about the sensitivity of the load if it receives AC power not within rated spec. I can't picture how this would affect the genset in any way, as it is a reasonable expectation it will be started with loads connected in any number of applications. The other side of that coin is if that could damage the genset, then it's not a very well designed or constructed product because it's not practical or reasonable to expect it will never happen. I haven't studied the Onan in detail (mine still works...) but it appears the regulator isn't controlling a whole lot of power and you'd think it would be designed to tolerate typical fault conditions like overspeed, load dumps, open/intermittent slip rings, etc. As evidenced by the troubleshooting steps and aftermarket module supply there are clearly conditions that cause them to fail so it's not "bulletproof" but when you consider how many of these things are out there and operate for a decade or more, they're fairly reliable. In my travels when stuff like this gives up it's not so much a sudden failure but an aggregate of contributing factors, like corrosion, dirt, wear, loose connections, etc that singly wouldn't cause a failure but together set up operating conditions outside of design boundaries.

Mark B.
Albuquerque, NM
 

DonTom

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Apr 21, 2005
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Auburn, CA or Reno, NV
In this new RV, it takes a good two minutes after the genny is started for it to transfer to the load.

But I don't recall any delay in my Y2K RV.

-Don- DeRidder, LA
 

dktool

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Apr 3, 2015
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153
On another related subject.....

While I'm monkeying with the generator I want to finally do some insulation that I have been putting off.
There is enough space in the box to put up to 1" on 4 surfaces.

What is the BEST for sound dampening through a spectrum of frequency ?
These slow rpm unit need more deadening in the lower end of the range.

This and a better muffler !
 

Lou Schneider

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Mar 14, 2005
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On another related subject.....

While I'm monkeying with the generator I want to finally do some insulation that I have been putting off.
There is enough space in the box to put up to 1" on 4 surfaces.

What is the BEST for sound dampening through a spectrum of frequency ?
These slow rpm unit need more deadening in the lower end of the range.

This and a better muffler !
I'd look at something like the Dynamat or Noico automotive sound deadening mats. I'm not sure if the manufacturer or the previous owner put them on the floor and doghouse of my front engine Safari but the engine is almost inaudible driving down the road - certainly quieter than the wind and road noise.
 

dktool

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Apr 3, 2015
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153
Update.....

So it turns out both the circuit board and the regulator were faulty.
After much probing / testing with the old Fluke I was pointing the problem more toward the circuit board than the regulator.
I purchased both, installed the new board with the old regulator and it fired right up and continued to run, (first victory)..but...the a.c. output voltage was 164v, so...plugged in the new regulator and now it's a rock solid 120v +- 0.4v

Next step is to verify hz with and without load per service manual and make adjustments if needed.

I scored the circuit board on Amazon listed as a like new, no box sale for $59.00 Prime + tax
All their other listings were @$146
The regulator came from getrvparts.com for $237 versus the going rate of $295 elsewhere.
So all in I'm at $329 for both..call it a win I guess.

Next is to do some insulation and possibly some exhaust mods.
Oh, and buy a Slick Stick.

Thanks again for the pointers fellas !

20220127_112217.jpg
Old junk
 
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dktool

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Apr 3, 2015
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153
I'm back with another question...

Does anyone know what the static main jet adjusting screw setting should be on this carb ?
My plastic "altitude reference" cap is missing and the manual gives no information on a x-many turns from all the way in for a starting point.
 

Lou Schneider

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I'm back with another question...

Does anyone know what the static main jet adjusting screw setting should be on this carb ?
My plastic "altitude reference" cap is missing and the manual gives no information on a x-many turns from all the way in for a starting point.
That was the problem with my $30 Chinese carburetor. The initial setting of the main jet was about 2 turns off on the lean side and it would stumble on acceleration (there is no accelerator pump). I would up taking off the cap and adjusting the screw until it was midway between stumbling on acceleration and obviously running rich. There's a point where the engine seems to take off and run easily and I left it there.
 

dktool

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Apr 3, 2015
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153
I played with the adjustment while running a 20 amp load on it, had to move it quite a bit in both directions to feel any obvious lean or rich conditions, then basically split the difference and left it there for now. It is 1-3/4 turns from full in.
I'll see how it reacts to various loading and likely make more adjustment, would like to fine the leanest spot with good "driveability"
 

Old_Crow

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Nov 20, 2016
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Tom's Place, California
I played with the adjustment while running a 20 amp load on it, had to move it quite a bit in both directions to feel any obvious lean or rich conditions, then basically split the difference and left it there for now. It is 1-3/4 turns from full in.
I'll see how it reacts to various loading and likely make more adjustment, would like to fine the leanest spot with good "driveability"

I just had the bowl off my Onan 7000. Let just a little too much time elapse between uses. I checked the needle before I removed it, and 1 3/4 turns out was where mine was at.
I dropped the bowl, cranked the motor and got no fuel. Messed with the float, sprayed some carb cleaner up into the needle and seat, and when I cranked it again, I got fuel flow. Put the bowl back on, set the needle to 1 3/4 and it now hums happily away. Ran it for an hour that day and then hit the button on the dash the next day and it started right up as normal.
 
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