Generator is dieseling

[rwmurphy15]

I have a 5500 Onan generator that runs good for about 5 minutes then it starts dieseling. It has 7 hours on it. Not sure what the problem is. Any suggestions.

[canesfan]

Mine had 12 hours on it, rig less than a year old. I had run it once a month for an hour under load as Onan advises. It got so bad it would shut itself off. Took it to Cummins, they replaced the carb first, then the fuel pump and fuel filter. They told me I did nothing wrong, it's the horrible ethanol fuel. Put Stabil and Sea Foam in it, too.

[rwmurphy15]

Canesfan, I did everything you did even ran it empty and even drained the bowl what little was in it for the winter. A couple days ago it was running but it had a slight putt or like a small miss. Now it's dieseling. Can you spray carb cleaner in it?

[canesfan]

I guess you can try carb cleaner. I had a nice long chat with the tech who worked on mine, and that's all he did, work on generators day in and day out. He said there's not much you can do once they get that way. That's why they don't even try to clean them, they just replace them. Thankfully mine was under warranty. I can't remember offhand if Onan gives you a longer warranty than Keystone, but I'd contact them and talk to them. They were very nice and helpful, very pleased with the whole procedure.

Here's their website for your area http://www.powersystems.cummins.com/locations.html

[rwmurphy15]

Canesfan,
I had some gum out carb cleaner so I removed the air filter and started the generator sure enough it started to diesel sprayed some carb cleaned into the carb and it stopped dieseling right away. It been running for 45 Minutes with no problem. I read on another site to get some Onan 4C spray carb cleaner that it works real good. Problem solved for now I hope! Thanks

[canesfan]

Glad you got it working. I think mine was too far gone for that. Hope it keeps working for you!

[rwmurphy15]

Well after 1 hour of running good it started to diesel again sprayed more carb cleaner did nothing kept dieseling back to square one again.

[denverpilot]

Just making sure I understand the problem since the phrase "dieseling" gets used incorrectly for many things.

Are you saying that when you shut off fuel and spark the engine keeps running?

Also since the Onan can be configured to run on gasoline or LP, you might mention which yours is set up for. I assume the assumptions here that you're running it on gas are correct.

Anyway... If a gasoline engine is continuing to run after switching off spark, you have pre-ignition happening.

Some basics: How old is the fuel you're running? When was the last time you had a spark plug out to look at the condition of the end of it?

Usually ... And I say usually with a large grain of salt... A gas generator that keeps running with no spark has carbon fouling around the valve area that's heating up and acting like a spark plug and igniting the fuel/air mixture before ignition is desired. Sometimes this is also happening well before TDC and can cause things to wear badly or break.

First off, if the fuel is old, dump it. Automotive fuel left for long periods of time in a tank will not be stable and won't have the properties needed for proper engine operation. In addition if it has ethanol in it, it likely will have a significant water content after long term storage. So many things caused by bad old stored gas without a stabilizer added to it.

Second, cleaning the carb is great but I don't see how it attacks your problem. If anything the carb is providing fuel (including idle fuel) just fine... Or it wouldn't be running with the ignition off. (Grin...)

Let's see if we are taking the same terms before going further. Getting the carbon deposits out if that's what's causing your pre-ignition is one step, and beyond that is finding out why it's fouling itself, which is likely a carb adjustment, not cleaning.

[canesfan]

Well, after denverpilot's fine post I realized I totally read the OP's post wrong. So my comments above do not reflect "dieseling". My generator was surging, and my comments reflect that. Sorry for the misunderstanding.

[rwmurphy15]

OK, Canesfan is correct the gasoline Onan 5500 generator is surging. Sorry for the misunderstanding Denverpilot of dieseling a friend of mind called it that. The fuel is new this year. Oil and filter is changed. 7 hours are on the generator. I use all non-ethanol with stabilizer and sea foam. I called Cummins today. They told me to run the generator for a hour or two even with it surging it may clean itself up. They said to remove the bowl to see if it is varnished. If it is then a new carb might be needed. He also told me that in the winter which I am in Penna that you must run the generator every month for 1-1 1/2 hours which I didn't it sat for 4 months not started but I ran the gas out of the fuel station then the generator ran empty another bad thing he told me not to do. Also this one had me confused but he said that stabilizers and fuel additive can clog up the fuel filter. As of now the generator is still surging some and I have and appointment on May 16. With Cummins. The generator is still under warranty BUT not if the carb is varnished. I'm going to put in new spark plugs. Then run it again this weekend.

[canesfan]

OK, now that we know for sure what it is doing...it is cheaper to replace the fuel filter than the carb. I've never heard of Stabil or Sea Foam clogging up the fuel filter though, but I learn new things everyday. My tech didn't say anything like that. As a matter of fact he told me to use Stabil. He also didn't recommend draining the bowl. He recommended running it an hour or more once a month, under load, which I believe is also in the manual. As for running it even with it surging, that's what I tried, along with adding a LOT of Sea Foam. It didn't help, it just kept getting worse to the point it would shut down. Thing is, it would start and run fine for a bit. That part never made sense and I never thought to ask him about that. Hopefully yours clears up, but with everything I know now I wouldn't get my hopes up too much. I think you're in for a new carb, hopefully under warranty. If I had it to do all over again knowing what I now know I would have gotten a diesel genny. But live and learn.

[rwmurphy15]

Canesfan, I agree with everything you said and I feel the same way. It seems sometimes when you talk to different technicians you get different answers from each. I wonder how well the propane Onan's work over the gasoline ones. Wouldn't have to worry about a varnished carb. I would like to remove the bowl but not sure how it comes off. Picking up new plugs on Thursday.

[Ken / Claudia]

I used the propane genny in my AF (Onan 2500 I think). Always ran great. I did run it almost every month as the manual says. Had it for about 10 years. Only problem ever was remote cold start. I had to bump the throttle link with a finger on every cold start. But, than it started right up. Changed spark plug several times and air filter but, really the old plugs always looked near new.

[denverpilot]

Glad to help @rwmurphy15.

I don't have any answers for you on surging on that unit as I don't know that one, but I've seen some lawn equipment and other things have a lot of problems with being stored half the year with this ethanol fuel we all have now. It seems to varnish and eat things it shouldn't in general.

On a couple of my smaller gensets and gas powered things, I've noticed that manufacturers are often putting instructions in their manuals about how to drain the carb bowl if the unit is going to sit for a while. Maybe there's a similar thing that could be done on the Onan.

Since its running, I kinda doubt you have a total crud blockage or eaten up completely seal in that carb, but you really can't tell much until it's off and opened up. Such a pain. Sorry.

I even have one snowblower that wasn't varnished or left with fuel without stabilizer in it where the old carb just croaked. I thought I would go get a carb kit and get on with the fussy job of rebuilding it and then found that the new carbs are a one piece unit and no rebuilt ever, it just gets thrown away if it has problems. That dried up the carb kit market for them and it was cheaper to buy the new carb than a kit. Amazing. Throw away society.

Good luck with it. Sorry it's being troublesome.

As far as your guy's advice to not drain but to run stuff every so often, that's what I try to do, but it's more like every two months than every month. The neighbors look at you funny when you drive the riding lawnmower out of the garage in the middle of winter on a sunny no-wind day! Haha.

[rwmurphy15]

Denverpilot, I wonder why Onan can't get away from the carburetors and go to fuel injected. Must be a lot of money made in repairing and replacing carbs.

[rwmurphy15]

Ken, did your Genny use a lot of propane. It's strange your owners Manuel still said you had to run it every month. What could possibly happen if you didn't run it for say 6 months.

[canesfan]

Couple of comments.

1. Re rebuilding carbs, I asked about that, just out of curiosity, the tech told me nope, not rebuildable. Fuel injection would be nice. I wonder too.

2. LP, the issue I don't like about that is you have to carry extra tanks around with you. I was next to someone a few years ago who had one. He had 3 I think 40 lb tanks, in addition to the 2 on his rig. This was for a 4 day weekend. To me that's a major hassle, to others maybe not so much. I've run my genny overnight a few times for a friend with a CPAP machine. It uses hardly any gas. With 2 30 gallon tanks I can go a long time without having to refill.

[rwmurphy15]

Canesfan, I also ask about rebuilding the carb or even removing it and cleaning it up. Same answer nope won't work, but he said they send back the old carb to the manufacture have them done over and resold as a new one. I told him that doesn't make sense. He said that the way we have to do it. Just sounds like a money making process. When you follow the owners Manuel to the "T" and thinks still go wrong it my fault. Go figure. On the propane idea yes it seems like a lost cause carrying around a lot of tanks.

[canesfan]

I love the part about how they send them back, "refurbish them", and resell them as new. If they aren't rebuildable, how do they refurbish them??? And I certainly don't want to pay "new" price for something that is refurbished and previously had issues. What a racket.

On another note, they never told me if it was varnished they wouldn't replace it under warranty. I told them what it was doing and he told me it needed to be replaced if that was the case. It was very cut and dry. They never looked at, never questioned it.

One thing to keep in mind, after he replaced it they ran it on a load bank for most of a day and it ran fine. When I went to get it he fired it up, it ran about 5-10 minutes and started surging again. He was totally embarrassed but said he was certainly glad it started doing it while I was still there and not after I had left. That's when they replaced the fuel pump and filter, which of course they were out of and had to get the next day. So I asked him instead of driving an hour home and back again if I could just take the trailer up the road to a local state park and come back the next day. He said that was fine. He called me and said everything was there and I could come in when I was ready. He stopped what he was working on, did the job, we ran it for a good while, we were both satisfied, and I was on my way, back to the state park to run it some more before I went home. So far, so good.

[rwmurphy15]

I think I will get a fuel filter and replace it that might work.