Onan 7.5kw Gen Problem

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Onan 7.5kw Gen Problem

July 02, 2021, 03:22:05 pm

This morning I started my generator. It started normally. I ran it for about three minutes, then loaded with fed roof a/c. After about ten minutes running, I noticed a change in sound of the generator and went outside to check. The generator was exhausting a little black smoke, which it has never done. I turned off the a/c, then shut down the genset. After a few minutes, I attempted restart. The gen cranks over but will not start. I checked main tank fuel and am at about half tank.

Any advice or suggestions will be much appreciated. I am fairly near the Cummins Service Center, but would really like to find something simple causing this.

P.S. After posting, I found an online reference that stated that the fuel cutoff is at the 1/2 tank level, not the 1/4 tank, as I had previously thought. If that's true, then my problem could simply be fuel starvation.

Re: Onan 7.5kw Gen Problem

Reply #1 – July 02, 2021, 04:49:37 pm

I don't believe either 1/2 tank or 1/4 tank estimates are correct. Here are several posts with Foretravel fuel tank drawings. All show generator pickup is 2.5 inches off the bottom.

generator shut down at 1/4 tank

Re: Onan 7.5kw Gen Problem

Reply #2 – July 02, 2021, 05:52:17 pm

Quote from: prfleming – July 02, 2021, 04:49:37 pm

I don't believe either 1/2 tank or 1/4 tank estimates are correct. Here are several posts with Foretravel fuel tank drawings. All show generator pickup is 2.5 inches off the bottom.

generator shut down at 1/4 tank

Thank you. Thus far, everything points to fuel starvation.

Re: Onan 7.5kw Gen Problem

Reply #3 – July 02, 2021, 07:28:17 pm

The easies way to see if you are out of fuel is as Chuck said on another post is to
get a container of fuel and hook it up to the fuel pump and see how it runs. Black
fuel usually means too much fuel.

Re: Onan 7.5kw Gen Problem

Reply #4 – July 02, 2021, 07:32:34 pm

Quote from: oldguy – July 02, 2021, 07:28:17 pm

The easies way to see if you are out of fuel is as Chuck said on another post is to
get a container of fuel and hook it up to the fuel pump and see how it runs. Black
fuel usually means too much fuel.

I'll definitely try it. Thanks!

Re: Onan 7.5kw Gen Problem

Reply #5 – July 02, 2021, 07:56:43 pm

Quote from: RandallBrink – July 02, 2021, 03:22:05 pm

This morning I started my generator. It started normally. I ran it for about three minutes, then loaded with fed roof a/c. After about ten minutes running, I noticed a change in sound of the generator and went outside to check. The generator was exhausting a little black smoke, which it has never done. I turned off the a/c, then shut down the genset. After a few minutes, I attempted restart. The gen cranks over but will not start. I checked main tank fuel and am at about half tank.
Any advice or suggestions will be much appreciated. I am fairly near the Cummins Service Center, but would really like to find something simple causing this.
P.S. After posting, I found an online reference that stated that the fuel cutoff is at the 1/2 tank level, not the 1/4 tank, as I had previously thought. If that's true, then my problem could simply be fuel starvation.

Naturally, the easiest way of telling is to first, add fuel to your fuel tank. After you do that, it may take a while to start unless you put the generator in the glow position which allows the electric fuel pump to run. If you have the small "T" handle valve that allows the fuel to go back to the take, you can open it with the fuel pump on and it will get the air out of the system. Without the hand operated valve that you can open, it takes longer as the electric pump does not put out enough pressure to push fuel and air past the fuel return (aka overflow valve) valve.

If the generator won't start, you can run a fuel line to a gallon container of diesel to have a known supply of fuel. If it runs, you have a fuel supply line problem. I'm assuming you have changed the secondary filter? If you have the barrel type of electric fuel pump, you can remove the bottom with a 5/8" wrench and clean the primary filter inside. Otherwise, there will be a plastic see through primary filter where algae or anything else is visible.

Any black smoke while the engine is barely running is from some injectors having no fuel but one or two remaining injectors do have fuel. The injection pump goes to full throttle and the one or two injectors with fuel try to carry all the load so produce black smoke in their max delivery mode. Cranking a cold engine with only one or two injectors having fuel may produce white/gray smoke.

Pierce

Re: Onan 7.5kw Gen Problem

Reply #6 – July 02, 2021, 08:32:29 pm

Quote from: Pierce & Gaylie Stewart – July 02, 2021, 07:56:43 pm

Naturally, the easiest way of telling is to first, add fuel to your fuel tank. After you do that, it may take a while to start unless you put the generator in the glow position which allows the electric fuel pump to run. If you have the small "T" handle valve that allows the fuel to go back to the take, you can open it with the fuel pump on and it will get the air out of the system. Without the hand operated valve that you can open, it takes longer as the electric pump does not put out enough pressure to push fuel and air past the fuel return (aka overflow valve) valve.

If the generator won't start, you can run a fuel line to a gallon container of diesel to have a known supply of fuel. If it runs, you have a fuel supply line problem. I'm assuming you have changed the secondary filter? If you have the barrel type of electric fuel pump, you can remove the bottom with a 5/8" wrench and clean the primary filter inside. Otherwise, there will be a plastic see through primary filter where algae or anything else is visible.

Any black smoke while the engine is barely running is from some injectors having no fuel but one or two remaining injectors do have fuel. The injection pump goes to full throttle and the one or two injectors with fuel try to carry all the load so produce black smoke in their max delivery mode. Cranking a cold engine with only one or two injectors having fuel may produce white/gray smoke.

Pierce

Pierce, thanks very much. I will tackle this first thing in the morning with your instructions. I have not yet changed any components, as this just happened earlier today. I can't get into Cummins for three weeks, so have plenty of time to try and resolve this on my own. I'll start with full fuel and see if that changes anything, then proceed.

Re: Onan 7.5kw Gen Problem

Reply #7 – July 02, 2021, 08:54:49 pm

Seeing that your coach is a 1989, you may want to get a good pair of glasses on or a magnifying glass and bend your fuel supply hose over on itself and see if there are lots of tiny cracks. I had a problem like yours and it ended up being the hose.

If it is the fuel hose, it can be replaced in a very short time. There is a Foretravel video of how to do it but I don't recommend doing it that way. The easy and fast way is to leave the generator in the normal position and not sliding it out. The fuel fitting on the tank can be reached by hand but you may not be able to get enough leverage to loosen it. I ended up using a crow's foot to break it loose. I don't recommend pulling the new hose into place by attaching to the old one. There are turns and kinks that can be avoided by using a long piece of brake tubing or other rigid material and attaching the new hose to it. You can push though the hole in the top right hand corner of the compartment and feed it all the way through to the tank fitting. I went to the auto parts store and bought a whole roll as it was cheaper than by the foot and I was assured that I would have enough. You can follow the old hose route in the generator compartment but be sure to allow enough hose so you can slide the generator out without stretching the hose. Ours had a different sized fitting at each end so go with the common size if both fittings are the same size.

Even if you have never done one before it can be done in anywhere from 15 minutes to one hour depending on the difficulty feeding the hose and removing the fitting at the tank. Like I said, a crow's foot on a 3/8" extension made light work of R&R of the hose and fitting at the tank. If you do that part first, you will have some extra hose left at the tank and that extra may be partially pulled into the generator compartment for the next step in the installation. Dependiing on the type of hose fitting, it may be push on or you may need a clamp. I like the fuel injection clamps that are smooth with a radius on the edge. They don't bite into the hose and don't let air in.

Pierce

Re: Onan 7.5kw Gen Problem

Reply #8 – July 02, 2021, 09:24:51 pm

Pierce,

I'll raise the coach in the morning and go under to see if I can do this. I'm at a disadvantage, as I am in the summer storage yard, not the garage, but will certainly see if I can do this. Thanks very much!

Re: Onan 7.5kw Gen Problem

Reply #9 – July 02, 2021, 11:04:31 pm

If your U300 is like ours, you can access everything with the fuel/propane compartment door open. Don't need to go underneath as the fittings and hoses are on the top of the tank. I can post photos if you like. It" no trouble as it's too hot here to do anything else.

Pierce

Re: Onan 7.5kw Gen Problem

Reply #10 – July 03, 2021, 10:04:18 am

Quote from: Pierce & Gaylie Stewart – July 02, 2021, 11:04:31 pm

If your U300 is like ours, you can access everything with the fuel/propane compartment door open. Don't need to go underneath as the fittings and hoses are on the top of the tank. I can post photos if you like. It" no trouble as it's too hot here to do anything else.

Pierce

Pierce,

I'm on my way over now to look at the lines and trace them between tank and generator. I'll look them over, fill the fuel tank, and see where I am at that point. Many thanks again for all the help, and I'll post results.

Re: Onan 7.5kw Gen Problem

Reply #11 – July 06, 2021, 01:57:11 pm

Pierce, (and everyone who posted a reply)

Thank you again for the assistance. I traced my fuel lines from tank to generator, and there was no evidence of leaking. But at the same time my generator problem seemed fuel-related,and I figured possibly a failed fuel pump, but while cogitating over that and while waiting for the appointment with Cummins, I kept tinkering...

I didn't feel I had a 100 percent accurate reading on my tank level, because my fuel "dipstick" was too long to go straight down into the tank, because of the fuel bay door. So I sawed it off to clear the fuel bay hatch and go straight down from the filler port. When I put the dipstick in, I felt and heard it contacting something in the bottom of the tank, which I assume was a float, and I tapped that gently a few times, read the fuel level circa 1/2 tank, then checked the gauge (slightly about 1/2 now) and attempted to start the generator. It fired right up. I ran it under load for a half hour, and stopped it, then restarted. Problem evidently solved.

Re: Onan 7.5kw Gen Problem

Reply #12 – July 06, 2021, 02:40:40 pm

Good news Randall. While your feed hose may not have been the cause, it's just about at the end of it's life if it's the same stuff that we have. I could not see the cracks in ours unless I bent it over.

Since it's summer and the AC may be needed, it may be a good time to make sure the generator belt is not loose and the hoses are in good shape. The bottom hose close to the crank pulley is prone to rot.

Pierce

Re: Onan 7.5kw Gen Problem

Reply #13 – July 06, 2021, 03:55:36 pm

Quote from: Pierce & Gaylie Stewart – July 06, 2021, 02:40:40 pm

Good news Randall. While your feed hose may not have been the cause, it's just about at the end of it's life if it's the same stuff that we have. I could not see the cracks in ours unless I bent it over.

Since it's summer and the AC may be needed, it may be a good time to make sure the generator belt is not loose and the hoses are in good shape. The bottom hose close to the crank pulley is prone to rot.

Pierce

Pierce, very good points. I may as well go ahead and do all that, as my maintenance record shows no indication of when those components were last changed.

Re: Onan 7.5kw Gen Problem

Reply #14 – July 06, 2021, 04:22:11 pm

Quote from: RandallBrink – July 06, 2021, 03:55:36 pm

Pierce, very good points. I may as well go ahead and do all that, as my maintenance record shows no indication of when those components were last changed.

Randall,

Here is a generator maintenance post I made eleven months ago. 10K PowerTech Maintenance & Modification You can make a visual on the bottom hose but if you need to change it, you can see the tools needed and how to do it. The breather mod was a slam dunk and really made a difference in the generator compartment. The existing OEM breather just dumped all the blow by on the floor of the compartment. The temp gauge and fuel pressure gauge are not super necessary but sure help to check operating temp and fuel pressure.

Pierce

Re: Onan 7.5kw Gen Problem

Reply #15 – July 06, 2021, 06:12:28 pm

Quote from: Pierce & Gaylie Stewart – July 06, 2021, 02:40:40 pm

Good news Randall. While your feed hose may not have been the cause, it's just about at the end of it's life if it's the same stuff that we have. I could not see the cracks in ours unless I bent it over.

Since it's summer and the AC may be needed, it may be a good time to make sure the generator belt is not loose and the hoses are in good shape. The bottom hose close to the crank pulley is prone to rot.

Pierce

Pierce, very good points. I may as well go ahead and do all that, as my maintenance record shows no indication of when those components were last changed.

Re: Onan 7.5kw Gen Problem

Reply #16 – July 06, 2021, 06:13:23 pm

Quote from: Pierce & Gaylie Stewart – July 06, 2021, 04:22:11 pm

Randall,

Here is a generator maintenance post I made eleven months ago. 10K PowerTech Maintenance & Modification You can make a visual on the bottom hose but if you need to change it, you can see the tools needed and how to do it. The breather mod was a slam dunk and really made a difference in the generator compartment. The existing OEM breather just dumped all the blow by on the floor of the compartment. The temp gauge and fuel pressure gauge are not super necessary but sure help to check operating temp and fuel pressure.

Pierce

Pierce, thanks much. I will definitely use and appreciate this guide!

Also, are you going with the Hardieboard in the gen compartment?

Re: Onan 7.5kw Gen Problem

Reply #17 – July 06, 2021, 06:39:59 pm

Quote from: RandallBrink – July 06, 2021, 06:13:23 pm

Pierce, thanks much. I will definitely use and appreciate this guide!

Also, are you going with the Hardieboard in the gen compartment?

Yes, but it's down the list a way. I should do it sooner, especially since we power the house with it during the many blackouts and leave the coach unattended for hours while it's running.

When you slide the generator out, check the exhaust system as our flex pipe had melted away the insulation and was burning the bulkhead plywood between the generator and fuel/propane compartment. Pretty easy to refasten it so it does not rub.

A lot more difficult backerboard installation as you need a motorcycle jack or forklift to remove the generator. Fortunately, the exhaust system and fuel system are on the opposite side of the engine. But, since I have not had time, I wanted to keep the oil deposits along with the absorbing dirt to a minimum so the breather modification was a good but stopgap measure to limit the combustible material. But you have seen how easily the black insulation burns so the big priority is getting it removed. Lots of coaches have the insulation hanging down onto the main engine or generator. Have you seen my insulation burn test? Sort of scary. Backerboard with fiberglass insulation underneath is excellent especially since fiberglass does NOT BURN.

Pierce

Re: Onan 7.5kw Gen Problem

Reply #18 – July 06, 2021, 07:52:03 pm

Quote from: Pierce & Gaylie Stewart – July 06, 2021, 06:39:59 pm

Yes, but it's down the list a way. I should do it sooner, especially since we power the house with it during the many blackouts and leave the coach unattended for hours while it's running.

When you slide the generator out, check the exhaust system as our flex pipe had melted away the insulation and was burning the bulkhead plywood between the generator and fuel/propane compartment. Pretty easy to refasten it so it does not rub.

A lot more difficult backerboard installation as you need a motorcycle jack or forklift to remove the generator. Fortunately, the exhaust system and fuel system are on the opposite side of the engine. But, since I have not had time, I wanted to keep the oil deposits along with the absorbing dirt to a minimum so the breather modification was a good but stopgap measure to limit the combustible material. But you have seen how easily the black insulation burns so the big priority is getting it removed. Lots of coaches have the insulation hanging down onto the main engine or generator. Have you seen my insulation burn test? Sort of scary. Backerboard with fiberglass insulation underneath is excellent especially since fiberglass does NOT BURN.

Pierce

Yes, I saw the burn test. As you may recall, I replaced my engine compartment mess with Hardieboard, per your instruction. I have peace of mind knowing that THAT compartment is fire blocked, but now I have generator compartment and refrigerator compartment on the list.

Re: Onan 7.5kw Gen Problem

Reply #19 – July 06, 2021, 09:13:14 pm

While the engine is surrounded by backerboard, a fire may not be noticeable for quite a while and unless the injector wiring burns up, it can continue to spread. A mechanical engine may be worse with nothing electronic to fail. IThe backerboard does give you a much bigger margin of safety and time to stop, safely evacuate and possibly fight the fire if it has not gotten too big. It also may give you time to unhook your toad. I use snap connects on the safety chains and never lock the hitch while underway.

On the other hand, if you do nothing, the black insulation acts like you sprayed gasoline on the fire.

A forum member with a U300 had some turbo work done. The clamp came off the turbo and the exhaust started a big fire. By the time he noticed it in the mirror and pulled over, he and his wife just had time to get out.

Engine fires are probably the worst with diesel or a broken hydraulic line starting and then feeding the fire. The refrigerator compartment is a slam dunk with the backerboard as there is very little hydrogen in the fridge and there is no way it will spread if the entire compartment including the ceiling is covered. With the insulation removed from the generator compartment and then the compartment lined on almost 3 sides, it's much safer but the compartment door has a lot of resin it it. If you had a generator fire, I can imagine what would happen when you opened the compartment door. Best be ready with a pretty good extinguisher and only fight it if you are experienced. One second of burns can change your life. Sort of like a back draft in a building fire.

I remember a big department store where a child at the back of the store was playing with his mom's lighter. It got into something flammable, he tossed it into some plastic goods and even though everyone in the store saw the fire, they just had time to get out the front doors. We were a couple of blocks away but by the time we arrived, the fire had blown out all the huge front windows and was extending into the parking lot.

Fire is really nasty and perhaps all the steps you take can give you or the fire dept time to fight the fire but WILL give you the time to safely evacuate your coach.

I've seen quite a few devices advertised to help protect from fire but many are of only marginal help in engine room fires while others may be able to stop or control a fridge fire. But as photos on this site have shown, they don't always work. Quite a few owners need a sense of security that buying such a device gives. Nothing wrong with buying and installing them but the only thing that is 100% sure is D and T. Just be aware and family plan for the emergency that could come out of the blue so you are able to have many other enjoyable adventures in the future.

Pierce

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