Onan generator runs only with cover off?

My Onan generator has only 55 hours on it. At the moment, it will only run with the rear cover off (which you are not supposed to do for long), or with the air filter cover removed, and the cover on. If I leave the air filter cover on, as I cover get within one inch of closing the access cover completely, the engine starts to idle down and sputters out as soon as the cover is closed. If I leave the air filter cover off, I get a bit of a sound when I approach closing the rear cover, but it stabilizes when closed.

When I bought the Westy a year ago, the generator wasn't running, so the seller had it repaired at an RV place which found nothing wrong but got it going. About 6 months ago when I started it, it was surging with very uneven idle. The next time I tried to start it for "exercise", it would not start.

It has taken until now to get to it. So far I have changed the oil, removed, cleaned, and re-gapped the spark plug (to .020"), tested for spark with a spark plug tester (positive), played with the circuit break up/down. There doesn't seem to be a 5amp fuse in mine (labeled as such near the circuit breaker under the generator access panel). I've also removed the air filter, which looks totally clean, and makes sense considered the nearly nonexistent use. I checked the black tube that comes down on the left for any obvious debris/bugs. Nothing I could see. So I took a turkey baster and tried to use vacuum motion to see if anything would come out. Nothing did (although the vacuum that I achieved was very weak).

When it still wouldn't start, I began playing with things with the rear cover off. What I found is that if I move the little black thingy which rotates and moves a little arm, just to the right of the air filter housing, it will start right up. This black thingy (sorry for the lack of tech terms) just rotates about 90 degrees with no spring tension or resistance. Then it will keep running (so long as the access panel is off or the air cleaner housing is uncovered but with the filter still in when the access panel is closed).

I can push another actuator arm, further to the right, to get more or less throttle. So that seems to work. Next I took the air filter out again and stuck my finger in the larger of the two holes. I could feel a valve/door of some sort in there. I can push this door to various open/closed states, and again there is no resistance or spring tension. Does anyone know if that is supposed to be like this?

I am imagining I have some sort of limited airflow issue, thus with either of the covers off, I get just enough air to make things run. If this points to an obstruction in the black tube, how do I clean that out? I cannot get this tube to pull out. And I am afraid that if I stick anything in there I will cause more damage. Is there any way to remove this whole tube? Is there anything else that could be wrong?

Oh -- one more thing to clarify: It doesn't want to start with both covers off unless I move the black thingy. Once I do while holding the start button (on the generator itself), I get instant start. It reminds me of a manual choke control on old cars. It seems if I hole start down for quite a while, once in a while I can get it to start with both covers off. But every time I fiddle with the black thing, I get instant start.

I am not an engineer or mechanic, but I can follow instructions. I have looked at the Onan manual and tried to research answers, but no success yet. Anyone have any suggestions?

Check th atmospheric vent. It is a little pipe sticking out of the Genny with a foam sock on it. A plug vent will result in strange behavior"

Icarus

icarus said:

Check th atmospheric vent. It is a little pipe sticking out of the Genny with a foam sock on it. A plug vent will result in strange behavior"

Icarus

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I second this suggestion. The bees that make shelters out of mud will go way up the tube clogging it. I had similar generator problem, and it was the bees.

Thanks, so I suspect this as well. How do I check this vent? I see it and it had no foam on it until a kind fellow Westy owner sent me some foam to zip tie on. I've previously stuck a wire hanger up in there, gently a few inches until it stopped. No force, but maybe that was not good. Then I tried using the baster in reverse to "suck out" anything that might be inside. I think the suction of that is too weak. I've never seen anything come out of that tube in my admittedly weak attempts. But it is apparently 23-25 inches long and I can only get a few inches into it. So the question is how do I clean this sucker out?

Remove it and blow it out or replace it. If you had no filter on the end for some time, it is quite likely it is plugged IMHO.

Icarus

Thank you, yes it seems signs point to this. But, do you know how to remove it? Can it be done with just the rear access panel off? I don't want to drop the whole generator. I need to work fast because it's in the 20s/30s here this week (I got spoiled by global warming). When I pull from the bottom, I get no motion. Can't tell where the other end is, or how it is attached/clamped inside. Access beneath the Westy in that spot makes it tough to see and do a whole lot.

Hi,
I’m assuming that you have the 2500 propane generator based from your description. To clean the vent tube thoroughly you have to remove it as Icarus instructed, you don’t want to stick a wire hanger all the way up the tube as it could damage the demand regulator diaphragm, and you also don’t want to create a strong vacuum in the tube for same reason.

Depending on model/spec, you can only access/remove the vent tube by opening the genset top enclosure that means you have to drop the generator first.

My LP2500 choke butterfly valve has a small return spring at the lever which keeps it in closed position when generator is not running. It takes several seconds to a minute to fully open the choke valve after starting your genset. Your choke valve could be slightly binding that is why you don’t feel the slight resistance of the return spring. You can easily clean and free the choke valve with carb cleaner, I do this every 6 months or so as preventive maintenance. I have dropped my generator several times for repair and maintenance; let me know if you need pictures of the inside that could help you.

Thanks, yes I have the Microlite 2500. I will try carb cleaner. So it sound like you're saying I should feel it return to closed position on its own, right?

Dropping the genset seems overwhelming but I would try it if I knew how. I assume you need some sort of jack underneath to support the weight while unbolting the supports. Then there is the LP gas line to deal with. How difficult is it to get the genset off and back on?

Having done a little research on genset removal, I fear this is too big a project for me, at least in the current winter weather. I found this post from someone who replaced that hose and fished the new one differently, without removing the genset. I am wondering if our 2500's have enough clearance to do something similar: http://usefulbulk.com/navionmods/onanhose/

Wasaabi said:

Thanks, yes I have the Microlite 2500. I will try carb cleaner. So it sound like you're saying I should feel it return to closed position on its own, right?

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yes

Having done a little research on genset removal, I fear this is too big a project for me, at least in the current winter weather. I found this post from someone who replaced that hose and fished the new one differently, without removing the genset. I am wondering if our 2500's have enough clearance to do something similar: http://usefulbulk.com/navionmods/onanhose/

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It is probably doable on some model/ spec. My Microlite 2500LP spec L has the vent tube mounted facing the rear of the genset, it would be hard if not impossible to remove it without removing the top enclosure. The vent hose end is also secured to the demand regulator with a spring hose clamp and needed to be removed or loosened first before the hose comes off. Yours could be different though. Although we have same genset model, Onan constantly changes its design and usually given with a different spec number designation. What spec # is yours?


Also, did you check if there is no debris blocking the air intake going to the air filter? I usually use compressed air to clean the air intake once in a while, just make sure you cover the openings (choke and breather tube) when you blast air in the area without the air filter.

Dropping the genset seems overwhelming but I would try it if I knew how. I assume you need some sort of jack underneath to support the weight while unbolting the supports. Then there is the LP gas line to deal with. How difficult is it to get the genset off and back on?

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I use a floor jack and piece of plywood to lower and support the generator while it is unbolted. You need a good ground clearance in order to roll out the generator under the RV once it’s lowered to the ground. I made a wooden ramp for the sprinter just for this purpose. Disconnecting the LPG line and (+) cable was easy. Disconnecting the genset AC wiring on my Agile for the first time was kind of tedious as I have to disconnect the wires from the ATF which is located inside the RV, I ended up adding an AC junction box just before the genset for easy wiring removal the next time.

Echoing what's above:

1) Clean the air filter and intake
2) Clean (carb cleaner) and lube all of the carb/throttle linkage (spray oil or silicone)
3) Clean the regulator vent tube. It is possible to work the majority of the length out without actually removing the generator or actually removing the hose from the generator. Put a pinch clamp or small vise grip on the hose as close to the generator as you can possibly reach - the idea here is to completely close the hose off so you can then use the turkey baster with warm water and clean out the now-accessible part of the hose. Squirt water into the hose and "work" the length of it with your hand or pliers...so if there is mud in there you can dislodge it and drain it out. If you get anything, keep doing this. As long as the hose is pinched shut you can even stick a piece of wire in it and it should not damage the regulator.
4) Let it dry, remove the pinch clamp, and hope it works. You can blow / suck on the hose end and actually hear the regulator operate if the hose is clear.
5) If all goes well and the issue is solved, remember to put a small piece of nylon screen or something over the end of the hose.
6) Also...but unlikely...these have a low oil shutoff. If your oil level is marginal, it seems like this could send a signal to shut down...perhaps intermittently.
7) Possibly...I think (?) there is an air vent on the front or side of the gen housing...make sure that is not obstructed by road gunk.

Good luck!
mogul2us

Thanks to both of you. Warmer weather is expected Friday at which point I will give it a shot without removing the genset. One question about "working out the hose": when I tug on the inch or so that sticks out from the bottom of the genset, I have no play. I cannot pull it out further. There must be something holding the hose there but I cannot see anything from my (rather awkward) vantage point under the van. Do you know if there is a clamp of some sort somewhere to loosen to get the hose to be more free?

Try driving the van up on some block in the rear to give you more room to work.

Icarus

For what it’s worth, you can actually blow and suck (no pun intended) into the vent tube and if it’s not completely clogged you could actually feel and hear the demand regulator diaphragm moves up and down as you do this (edit: mogul2us already mentioned it). The vent tube is about 25 inches long and routed in-between the LPG mixer and the stator housing then exits to the side air vent, there are no clamps holding it at least on mine. Personally, I would not use wet lubricants on the linkages as it tends to attract dirt which may cause binding issues later, you could try dry lubricant instead if you wish.

There could be many things that could cause the genset to shut down, like air/ fuel, oil issues, mechanical and electrical problems. You have to start where the symptoms is pointing you and worked from there thru process of elimination. Most diagnosis could be done without dropping the genset. I’m no expert on this and just responding mostly based on my experience with the same unit.

If after cleaning as suggested and symptoms remains, I have questions for you, does your genset fires right away after it shuts down? Does it need to cool down first before it fires again? Do you need to hold the start switch just to keep it running after it shuts down? Also observe if the choke opens up after the genset warms up, you could see it fully open in less than a minute or running.

Rather than pulling the hose from the bottom, try pulling it up from the top. It will take a little manipulation with your fingers, but it can be done (at least I did it). You can also put it back as well.

mogul2us

Ok so my plan was to get to this today, since it is nice and 50 degrees. Unfortunately I threw out my back (ugh!). Bad timing. But since I am stubborn, I'm going to try to get out there (against common sense) and see if I can do some spraying and free up that hose without straining myself too much. Thanks for all the encouragement on here. So helpful! Will keep you posted...

So I got to the generator this weekend. Not resolved yet, but progress and a bit of a puzzle.

First, I did find that the air valve was sticking and not springing back. Closer observation revealed that the spring was not connected to the tiny metal tab that controls the valve. I managed to get the spring back on, and clean out and lube everything with dry lube. Now I can feel the light spring action pulling the air valve closed.

I managed to get the vent tube out about 5 inches. I then clamped the tube above inside the genset. Could not tell how far up I clamped it because of the way it wind around inside. Next, I decided to insert some weed trimmer line to see how far up the clamped spot was. It was 10 inches or so. The line went in with no restriction, so I opted not to clean anything at this point. Instead, I removed the clamp, and decided to see how far up I could get the line. I was gentle and at about a foot and a half, I decided to stop for fear of damaging the diaphragm at the end. When I pulled out the trimmer line it was totally clean. So I figured, what the heck, I might as well try the blow/suck routine on the vent hose to see if I can feel the diaphragm moving. I could feel the diaphragm's click when I did this. I wouldn't say it was easy to get the diaphragm to "click", and I'm not sure if that means the vent is partially obstructed. But it wasn't hard either -- more force than it takes to suck a beverage with a straw, but less than blowing up a beachball at the end.

The result: the genset now starts right up. But, it doesn't want to keep running. If I keep the plastic air filter cover off, and of course put the main access panel back on, it will start up and run beautifully. Even load tested with a 1500 watt heater and the idle adjusts beautifully. But as soon as I put the plastic air cleaner cover on, it starts some uneven idle and then dies.

Inspecting the plastic cover, I see that someone had drilled 4 holes into it, perhaps to help it suck air in. Kind of odd, but I thought maybe I could drill more holes into it. I tried drilling more and more holes until I had 12, but still no difference. I then taped up all the holes, to see if maybe it was causing the problem. No difference. Will only run with the plastic air cleaner cover off. It is as if there is very little coming into the air intake. But there is also no obvious obstruction that I can tell.

You've all been so helpful, thank you! Now, any ideas on what to try next? Also, since it is colder here for the foreseeable future (or at least until we head out later this month), I wonder--is there is any problem if I run the genset with air cleaner cover off until I can fix this? Will anything get damaged? The access cover will remain on.

Being an experienced armchair Internet expert mechanic, I'd suggest changing the air filter. OneManVan posted the part number in an earlier post.

It'd be a cheap part to replace in a "replace parts until it works" approach. Sometimes things may look like in good shape but get distorted when in use.

Fyi: Dr A warned against using generic Sprinter air filters which fell apart and caused a lot of engine damage.

If don't do that, at least confirm it's the right air filter and in good condition.

Then maybe consider replacing the air filter cover. There are weird things which sometimes happen when things don't fit right (like the rubber spacers on the awning window screens).

You've already checked for obstructions but maybe double-check wherever the air is supposed to get into the air filter.

Maybe go ahead and do an oil change while you're at it. Or at least confirm oil level is at right level.

Good luck. Keep us posted.

Oldwest, I like your suggestions. The filter looks totally clean but who knows. Can't hurt. I will replace the cover too. The oil was just changed and I confirmed correct quantity. The genset sounds really great and healthy without the air filter cover on. I wonder, if there is a way that I can tell if there is any obstruction in the incoming air flow. I can see in the top of the air compartment under the filter that there is a small passage from where the air comes. Presumably this duct winds down and sucks in air from the left side of the genset, where there are some openings towards the front. I tried putting my trimmer line into the duct to see if I could catch where it comes out. It gets stuck somewhere, maybe because of a bend. So in theory there could be a dead critter of some sort in there and I wouldn't know. I wonder what is the process to clean out the air intake duct?

(I am starting to feel a bit like a caveman trying all sorts of different things, banging here and there, sticking things in various spots, with this genset...)

Well the good thing is that it works under certain conditions.

In my first couple months of ownership, my generator conked out. Had to take to a higher level Onan service center in Nevada (funny--folks were working on huge diesel engines in these big buses (Cummins) and my dinky little Onan propane generator). Found an obstruction in the propane line/valve so had to replace some valve in the rear of generator--tech thought maybe poor installation was cause but still replaced part under warranty.

I did pay extra for them to install snap-disconnect-release connections on the various wires for easier future removal.