So I've been trying to track down this issue I have been having with my 5500 Cummings/Onan generator. It will die out intermittently. I finally tracked it down to it dies when you hit a very rough highway or harsh jolt from a dip on a bridge expansion joint. And I diagnosed it even further in that it does it only when hot outside 85+ degrees. I found that if you give the generator a good push/shake it will want to die or will die. It doesn't do it when it 85 or less. It has a complete tune up, filters, oil plugs etc. I'm going to clean the carb and maybe decaf in it. It has 370 hours on it. But it's not a runny no idling problem. I believe the gas in the carb is boiling and when it gets shaken hard it sucks the air from the boiling gas. Has anyone run into this. I was going to install some type of vent on the outside generator door, but when I open the compartment it's not hot. When I open up the generator cover you can really feel the heat, which is why I'm think the fuel is boiling when it's hot outside. The generator will run with no issues when it's below 80, it never dies then!I have an outdoor thermometer in one of my compartments for outside use. I have seen storage compartment temps over 110 degrees. My gen is at the LR so it's getting all the heat sucked into it instead of cooler air. Anyone?

I've got the 4K version and I think you've described what ours does to a "T".Today it's upper 90's and the generator just shut it self off while we were sitting in a parking lot. I popped open the door and it's an oven in there. I've seen people cutting the door up and installing a DIY grill.I'm thinking of doing that to try to help dissipate the heat.

It was the altitude adjustment screw for me, the cooling on the 5500 is a closed system with directional air.

I have heard of people putting a fan in that area to remove the heat and some would just open the door when stationary.

On mine I replaced the fuel pump and solved all the problem.

PastorCharlie wrote:On mine I replaced the fuel pump and solved all the problem.My first thought also. Gasoline will boil at 180 degrees but I think the fuel pump gets a bit wonkers first and shuts off.I would hold off doing and owner mods to the shell of the generator. Cutting vents or such is a bit of a last resort option to me considering the difficulty to restore to original state. The 5500 is very common, has been around for a number of years and is designed to keep it's self cool with all the access panels in place. If there was a cooling issue it would show up in just about ever generator in use and wold be an endless thread on the various RV forums.

Generator vapor locking | Good Sam Community

Gonefshin
Explorer
Apr 23, 2021
For those with the Onan 4000 generator, they make a vent to install in the compartment door especially for it. It separates the cooling air from the hot exhaust air from underneath the rv. Works great.
dodge_guy
Explorer II
Apr 19, 2021
I forgot all about this thread. Well I installed a new fuel pump and it was doing the same thing. We took a trip down to FL in mid October and the generator ran an entire day without issues. Yes it was in the 60’s outside. So what I did this year was install a set of stainless vents in the lower part of the generator door. This will feed cooler outside air to the generator air intake and expel the hot exhaust (not the actual exhaust!) I have upper vents ordered as well to vent the compartment. I forgot to mention that I put my little outside temp gauge in the compartment last year and the temps were near 200 deg. Seems a bit hot for an air cooled generator. So my thinking is the fuel is boiling in the carb and when it gets jarred it moves the air bubbles and the engine sucks in no fuel. I tried disconnecting the oil switch and no fix. I did try a new one and same results.

I feel confident this will fix it. The front vents are faced forward and the rear ones to the back to remove the hot air.
Digisonic
Explorer
Apr 19, 2021
Hey everyone, I'm a new RVer here in 2021. I have a 2008 Fleetwood Fiesta. I've been reading tons of people having this issue of the generator shutting down only while driving. IT could take anywhere from 15 minutes to 2 hours in hot Southern weather. I replaced the fuel pump and fuel filter. It is NOT that. It seems to be poor air ventilation. A Fleetwood Class A owner with the same Marqui Gold 5500 Onan generator on the FMA website back in 2015 had Ancira RV in Texas install an air ducting kit with an air vent on the Generator door. It seems now Ancira and even the Fleetwood dealers know nothing about this kit that was supposedly gotten from Fleetwood. I can't get though to Fleetwood. I just get stuck in their phone system recording loops. Does anyone know about this air duct kit, have a part number, know where and how to get this kit?
hohenwald48
Explorer
Jul 23, 2020
dodge guy wrote:
hohenwald48 wrote:
You can get the fuel pump on Amazon for around $30. Let us know what you ultimately find to be the problem and good luck.

Thanks. The cheap ones seem to be off brands. I wanted to go with the Airtex because they are the ones that supply Onan with the fuel pumps. However, if the oil pressure switch doesn't fix it I may just go with the he cheap pimp for now and see how it does. If it does fix it then I will get the better pump when it becomes available.

Yeah, I know what you mean. The last cheap one I bought only lasted 7 years. Pure junk.
GREGORYJ
Explorer
Jul 23, 2020
After the generator stops after running and is hot, press and hold the generator primer button, if you don't hear the normal pulsing sound of the electric fuel pump, it has likely seized. After it cools, try holding the primer button again, if you hear it, the generator will likely start and run again till the pump gets hot then seizes again. Replace the pump. The Amazon replacement pump worked well for me. With the generator running, the electric fuel pump should run continuously, but you just can't hear it over the generator's noise.
Stim
Explorer
Jul 23, 2020
You should be able to check the switch just by unplugging it.
Mr Gasket sells different psi fuel pumps and you can get them at most auto parts stores.
They even make a diesel fuel pump (green), I have one for the lift pump on my farm tractor.
dodge_guy
Explorer II
Jul 23, 2020
hohenwald48 wrote:
You can get the fuel pump on Amazon for around $30. Let us know what you ultimately find to be the problem and good luck.

Thanks. The cheap ones seem to be off brands. I wanted to go with the Airtex because they are the ones that supply Onan with the fuel pumps. However, if the oil pressure switch doesn't fix it I may just go with the he cheap pimp for now and see how it does. If it does fix it then I will get the better pump when it becomes available.
hohenwald48
Explorer
Jul 22, 2020
You can get the fuel pump on Amazon for around $30. Let us know what you ultimately find to be the problem and good luck.
dodge_guy
Explorer II
Jul 22, 2020
4x4van wrote:
If it was vapor lock, it would not start right back up; it would require a bit of cooling down time. JMHO.

I agree. And the more I have been thinking and researching, the extended crank time after it dies leads me to believe the carb is running empty. And the extended cranks fills the float bowl. I may end up trying an oil pressure switch. The fuel pump from Airtex (the company that supplies them to Onan) is on back order. And I don’t want to spend $150 for a fuel pump just because it says Onan. So I may try that first.
Bruce_Brown
Moderator
Jul 22, 2020
dodge guy wrote:
Bruce Brown wrote:
dodge guy wrote:
It very well could be a fuel pump. If it were weak Pump) and electric pumps are known to work at slower speeds when they get hot) would Cause the issue I’m having. I can’t see it being an oil issue only at hotter temps. I will try the pump first. If not then I’ll do an oil switch. If it were an oil switch issue it should give a code on why it shut down. I never get a code. There is no code to be set for low fuel flow. So if it died due to low fuel it wouldn’t set a code.

It's your money so do what you want.

If it were my money I'd start with the oil switch as Doug suggested. Pretty cheap and easy to try, and 100% makes sense as to what is happening, as he explained.

With that said, we once owned a Ford powered MH that would die when it got hot - it was the fuel pump. The big difference is that one wouldn't immediately re-start and run well. Sometimes it would re-start and limp, sometimes it wouldn't re-start until it had cooled.

You guys are aware this is the Generator engine right? The generator runs In completely different parameters than the vehicle engine.

I've very aware. My note on the MH was yes, a hot fuel pump may indeed be an issue. With that said, it made no difference if it was rough or smooth, when it died it died. It was 100% a temperature issue and 0% a terrain issue.

In your case the fact it only does it only when you hit a bump or shake it leads me to believe the switch is more likely to be the issue. Keep in mind heat effects electronics too.

But like I said, it's your money. If you want to start with a $45.00 pump first it might save you from buying a $4.00 switch later. Me - I'd rather start with the $4.00 switch in hopes I'd be saving $45.00 later, but thats just me.

I'm sure you'll get it figured out and let us know - and we'll all appreciate your information!

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