Onan emerald plus generator turning off.

[OTGT]

I am posting my problem to see if anyone has a solution for this weird issue. My problem is, when I start the generator with the motorhome engine off, it will run great all day and night. But, if I start the front engine and start driving down the road 15-20min later, it cuts off. Here is what I've done so far.

Replaced fuel filter
decarbonized carb and cylinder
took the carb apart and it's like new, it may of been rebuilt recently
changed oil and filter 30w HD

What could cause the generator to quit only while going down the road?

The generator runs smooth even under high load. 

 

[Weewun]

Sounds like you are starving for fuel.  I would check the Fuel Pump pressure.

 

[Clay L]

I had a similar issue and it turned out to be a loose hose clamp at the transition from rubber fuel line to metal near the gas tank that was allowing air to sucked in. The vibration while going down the road appeared to allow the air in.

 

[OTGT]

I guess I'll go ahead and replace the rubber fuel line from the tank to the the pump.  If it the fuel pump pressure, how do I test that?

 

[Mark R.]

This may sound silly but you may want to leave your gas cap loose and drive the rig, if the old cap does not allow air into the tank fast enough you can have a vacuum that will stop fuel from going to the gen.

 

[Mark R.]

Do you know what year and size of your gen?

 

[OTGT]

Do you know what year and size of your gen?

It's a 1990 onan emerald plus 4000 watts.

 

[OTGT]

This may sound silly but you may want to leave your gas cap loose and drive the rig, if the old cap does not allow air into the tank fast enough you can have a vacuum that will stop fuel from going to the gen.

I always thought it had something to do with the fuel system. I know it has a low pressure fuel pump so it doesn't take much to stop the fuel flow. I will give that a try tomorrow.

 

[OTGT]

Ok, I loosened the fuel cap and the problem persists. I'm also noticing it's not turning back on right away. I have three theories of what it could be. Pplease comment on what you think it is. 

1. The low oil sensor is bad and causing the gennerator to turn off.

2.  The board or circuit in the generator is getting hot or sensos a heat issue and shutting down the Benny.

3.  The fuel pump weak is bad. Not sure if it would work at all if it was bad but I'm stumped at this point.


I realy want to try to fix this issue myself instead of paying someone $100+ per hr to try to fix it. 

 

[Mark R.]

Why only when rig is moving, to all of your scenarios, and they are good guesses.


I fix everything myself so I agree, due it yourself.

Is gas tank fairly full, dip stick will not go to bottom of tank in most MH's?

Dip stick could be broken off and slosh could make it suck air when driving.

If I were you I would isolate problem first, I would go buy some gas hose (rubber) and connect to generator , and depending on what you have , outboard motor tank or a friend holding a gallon of gas and start a siphon to the generator and take a ride , crude but it may tell you where to look, and it should only cost a few bucks.

I base these things to try on your statement that this only happens when underway, so I am assuming you have looked for mouse nest that will cause overheat shut down and oil levels , bad electrical connections and loose or deteriorating gas hoses,  older gas hose can deteriorate from the new alcohol.

If you have the print for unit you may be able to jump out inputs to the control board or find out the resistance readings for sensors and replace them temporarily with a resistor.

Good luck, you will fix it, its just one stupid problem you have not found yet. let us know what you find.

 

[OTGT]

Why only when rig is moving, to all of your scenarios, and they are good guesses.


I fix everything myself so I agree, due it yourself.

Is gas tank fairly full, dip stick will not go to bottom of tank in most MH's?

Dip stick could be broken off and slosh could make it suck air when driving.

If I were you I would isolate problem first, I would go buy some gas hose (rubber) and connect to generator , and depending on what you have , outboard motor tank or a friend holding a gallon of gas and start a siphon to the generator and take a ride , crude but it may tell you where to look, and it should only cost a few bucks.

I base these things to try on your statement that this only happens when underway, so I am assuming you have looked for mouse nest that will cause overheat shut down and oil levels , bad electrical connections and loose or deteriorating gas hoses,  older gas hose can deteriorate from the new alcohol.

If you have the print for unit you may be able to jump out inputs to the control board or find out the resistance readings for sensors and replace them temporarily with a resistor.

Good luck, you will fix it, its just one stupid problem you have not found yet. let us know what you find.

I think you hit the nail on the head. I did alot of thinking on what I'm doing when the problem occurs and now everything is making sence. I remember when I filled up my gas tank, I was able to go a long ways before the generator turned off. Now that I have a half tank, it turns of fairly quick while going down the road. Yet, with the engine and the gennerator running with the coach parked, everything runs fine. I found out today that my generator has a pressurized oil system , not a slush system, hence the oil filter it has. I think the litthe tube that goes into the tank has an issue like it's cracked or is not moving with the gas allowing air into the line and killing the gas to the genny. It also can't be the fuel pump because it worked fine when it sat still. I will run a dedicated fuel line from the generator the a gas canister and go down the road and see if the problem goes away. I will let you know if this worked or not. If it is the pegilum piece inside the gas tank, how do I fix that?  

 

[OTGT]

Ok, I got a tech to drop the tank and everything is solid. The inside of the tank is very clean and the are no cracks, he's or anything in the aux pipe going into the tank. This Friday, he is going to add another couple inches to the aux pipe (generator pipe). Is that wise to do? It won't be at the bottom so these no risk of running out of gas. We are also replacing all the rubber hoses to see if that will help but still can't find the direct problem. Again, when my gas tank is full, it will stay on for quite some time going down the road before turning off. When it gets to about 3/4 to 1/2 tank, it starts cutting off like there is a fuel issue. Sometimes, I can turn it right back on and sometimes it won't stEt at all for a while. I have a couple more theories and wonder what you think.

1: could the fuel pump be getting weak and as thegas in the  tank drops, theres less pressure on the fuel and the pump is having trouble pumping the fuel?

2: could it be a float issue in the carborator not replenishing fuel properly?



I talked to a cummins tech last week and it had him stumped. He told me to drop the tank to be sure there's nothing wrong with the lines but Gain, everything looked fine. Please Any advice is greatly appreciated.

 

[Mark R.]

I was wondering how you made out, week or internal bad pump, could be, float in carb not likely. how high off the ground is the carb compared to the level of fuel in the tank. If gas is above carb you could be siphoning gas until fuel level gets below carb and then it would stop if pump is not pumping fuel.

I like to be able to use the gas in the tank for the generator if I want, all I need is enough gas to get me to the next station.

Did I read that you replaced or cleaned generator fuel filter?
I assume you have looked over the rubber fuel lines .

keep us updated and good luck.

 

[OTGT]

I was wondering how you made out, week or internal bad pump, could be, float in carb not likely. how high off the ground is the carb compared to the level of fuel in the tank. If gas is above carb you could be siphoning gas until fuel level gets below carb and then it would stop if pump is not pumping fuel.

I like to be able to use the gas in the tank for the generator if I want, all I need is enough gas to get me to the next station.

Did I read that you replaced or cleaned generator fuel filter?
I assume you have looked over the rubber fuel lines .

keep us updated and good luck.

The carb is level at about the halfway mark on the tank. I didn't think of it that way but you may be right. I may go ahead and replace the pump just in case. I know it has to be working some at lease but I guess sometimes they get just weak. It looks like the original pump so at 19yo, it's time. I will let you know the outcome.  Thanks

 

[DonTom]

The carb is level at about the halfway mark on the tank. I didn't think of it that way but you may be right. I may go ahead and replace the pump just in case. I know it has to be working some at lease but I guess sometimes they get just weak. It looks like the original pump so at 19yo, it's time. I will let you know the outcome.  Thanks

Is that a gasoline genny?

If so:

Intermittent ignition problems seem exactly like intermittent  gas problems. No spark explosion  in either case. I mention this because I had a problem that I assumed was fuel related on a motorcycle. It would cut out at 60 MPH and all sorts of power back at 50 MPH or below. When I gave up on checking fuel stuff, I rode with a voltmeter going to the primary of the ignition coil. I lost DC to the coil at 60 MPH. It was caused by the vibrations causing the ignition switch to open. I fixed that problem with a relay to reduce the "bounce" in the contacts, as well as change the switch to a different style.

If it only happens on the road, try to find out if it's affected by vibrations if you can think of a way to do such a test. See if you can check the genny primary coil voltage while on the road. Run a wire to inside where you can see on a voltmeter. An analog meter would be best for this test.

I would still check for fuel problems first, but do NOT assume it must be a fuel problem.

-Don- SF, CA​

 

[Ernie n Tara]

I had a similar problem on a 96 Flair. It turned out that the gas line at the filter input (engine end of the steel line) was leaking air. I swear it looked good, but I replaced it and never had the problem again. Note that the generator ran fine until I got down to half a tank or thereabouts and then the gen quit.
Good luck,
Ernie

 

[crosscountry]

My generator shuts off when the fuel level reaches I believe 1/4 tank.

Possibly bouncing down the road shuts yours off as it reads less fuel in the tank then required.

Russ