Generator Surging Issue

[justAmanda]

Hello! I have a 2017 Ford T350 XL that's been fitted into a dog grooming RV by Wagntails. I've encountered a strange problem and would love any feedback or advice. It uses an Onan 7000 HGJAD model but recently has been having trouble starting up and then began surging under moderate load. If the load was lessened it would even out but now it doesn't even turn on without immediately surging and won't provide power.

Yesterday we took out the generator and put in the backup (same model) that had just been checked out by Cummins and had been running for hours there with no issue. It did the exact same thing once back in the van. That was really heartbreaking!

This leads me to suspect the issue is in the RV part of the truck and not the generators themselves. Could it be the control module? I have never seen it in this vehicle and have no idea where it might live if that's the case. Thanks for reading!

 

[RRR]

Gas, running off the fuel tank of the RV? Restricted or pinhole leaks in the line.

 

[justAmanda]

Gas, running off the fuel tank of the RV? Restricted or pinhole leaks in the line.

It does use the same fuel as in the vehicle's gas tank. Do you think checking for restriction or leaks is a task for a mechanic or an RV specialist?

 

[John From Detroit]

I agree with fuel line issues as the most likely cause.
Surging indicates as I recall a "rich" fuel/air mix however )(Assuming gasoline engine if diesel forget this post)_ Google says I might be wrong however they say:

• Fuel: Low fuel pressure, weak fuel pump, or clogged fuel injectors
• Air: Dirty or faulty mass airflow sensor, vacuum leaks in the intake manifold or vacuum hoses, or dirty throttle body
  
  Now most of that does not apply to the generator but low fuel pressure. weak fuel pump. Clogged fuel outlet screen (inside tank_.
  
  If I'm right dirty air cleaner can do it too.

 

[justAmanda]

Thank you! Do you think my regular vehicle mechanic could help diagnose a fuel issue or would an RV place have better luck?

 

[justAmanda]

It is gasoline, not diesel

 

[DonTom]

then began surging under moderate load.

Could it be trying to put itself back on 3,600 RPMs (60 hz frequency)? Did you check to see what the frequency is? It could be surging from the RPMs not being correct and then it tries to but itself back on frequency, IIRC when about 5 hz off in either direction.

Every 60 RPMs equals 1 hz. 60 times 60=3600 RPMs.

IOW, could be a simple speed adjustment. The frequency (RPMs) is probably dropping under the load. IOW, increase the RPMs a little and see what happens.

-Don- Auburn, CA

 

[justAmanda]

I'm not sure I have the technical prowess to increase the RPMs without messing up something else but I'm grateful for all the ideas and feedback. Thank you all so much!

 

[DonTom]

I'm not sure I have the technical prowess to increase the RPMs without messing up something else but I'm grateful for all the ideas and feedback. Thank you all so much!

It's not difficult, just use a cheap Watt-o-meter to check the frequency. If off more than a few hz from 60 hz under load adjust the screw thingy on top of the genny to change the speed. You could want it a bit high with no load, such as 63 hz and perhaps 57 hz with a full load. 60 hz with a moderate load. But whatever works.

But if you really want to do it the correct way (I normally don't have the patience for that!) you can read the service manual procedure for the speed adjustment. I never bothered to look at it myself, as my genny is working as well as it should with my mickey-mouse DonTom style adjustments.

If on 60 hz and is still surging, only then do you know you have an engine problem. And I doubt that, sounds like the typical off freq thingy to me and then it is self-correcting causing the surging.

-Don- Auburn, CA

 

[John From Detroit]

Could it be trying to put itself back on 3,600 RPMs (60 hz frequency)? Did you check to see what the frequency is? It could be surging from the RPMs not being correct and then it tries to but itself back on frequency, IIRC when about 5 hz off in either direction.

Every 60 RPMs equals 1 hz. 60 times 60=3600 RPMs.

IOW, could be a simple speed adjustment. The frequency (RPMs) is probably dropping under the load. IOW, increase the RPMs a little and see what happens.

-Don- Auburn, CA

I think ONAN's run at 1800 or 1200 (3600/N) there are ways both electrical and mechanical to double or triple the output frequency Interesting in that GOOGLE says
RPM of 2,880.

I do not know how they do 1.25 times motor speed unless it's a belt drive.

 

[DonTom]

I think ONAN's run at 1800 or 1200 (3600/N) there are ways both electrical and mechanical to double or triple the output frequency Interesting in that GOOGLE says
RPM of 2,880.

I do not know how they do 1.25 times motor speed unless it's a belt drive.

I was somehow thinking it was a 4K genny, but I now see it is a Onan 7000 HGJAD, which runs at 2,400 RPMs.

But it still has to be 60 hz, and it probably adjusts in a similar way. Checking the freq is a good place to start.

-Don- Auburn, CA

 

[Gary RV_Wizard]

The immediate problem is probably what has been suggested - the generators speed governor is attempting to maintain 2400 rpms as the load changes. However, that is not a problem to fix by manual adjustment. The issue is that the governor is failing to do that, and that almost surely means a fuel delivery problem. As the load increases the governor opens the throttle to get more fell into the engine to handle the load. If it can't get enough fuel to run steadily, surging results.

My first though is a fuel filter or screen (if it has one) and next is an air leak in the fuel line. The generator fuel pump sucks gas from the van tank, so even a tiny leak pulls air bubbles ino the fuel line.

A regular vehicle mechanic might be willing to try finding a fueling problem, but most would probably recommend a generator specialist.

 

[justAmanda]

Hello all! Today the generator decided to change things up. Instead of struggling to start up and surging immediately it started up, gave me AC power, and was running steady. I measured the frequency with my fluke multimeter (digital so hard to misread it too!) and while running normally it was at 60!

Turned the air conditioner on and it jumped up a bit to 60-65. When I turned on one of the two blow dryers that's when things got crazy. It was all over the place up to 100! When I turned on both dryers it actually jumped up less dramatically.

I think the vehicle's fuel line is my most probably suspect now. Not with two running generators that suddenly have the same issue once back in the vehicle.

Thank you everyone for helping and any other ideas or advice will always be appreciated!

 

[Kirk]

I think the vehicle's fuel line is my most probably suspect now.

If yours is like all of the Onan generators that I have had or worked with, the fuel pump is mounted on the side of the generator, so it should be very easy to check that out. Just get 3' or so of rubber fuel line hose and attach one end to the inlet to the fuel pump and put the other end into a 5 gallon gasoline can. If your fuel line is the problem this should make it run just fine.

 

[DonTom]

It was all over the place up to 100!

That was probably electrical noise interfering with your meter.
Also, it could be it will not respond well to fast changes in frequency.

A kill-o-watt meter will more likely be steadier on its freq selection.

IAC, I don't buy for a second that the genny was running at 100 hz.

-Don- Auburn, CA

 

[John From Detroit]

I was somehow thinking it was a 4K genny, but I now see it is a Onan 7000 HGJAD, which runs at 2,400 RPMs.

But it still has to be 60 hz, and it probably adjusts in a similar way. Checking the freq is a good place to start.

-Don- Auburn, CA

Yes I agree on plugging in a Kill-A-Watt and hitting the Hz button.
Likely they use a belt drive to get it up to 60 hz.

 

[Ray-IN]

Thank you! Do you think my regular vehicle mechanic could help diagnose a fuel issue or would an RV place have better luck?

Regular auto/truck mechanic. The only thing "RV" is where it's used.

 

[justAmanda]

Hello everyone! Thank you all for the helpful suggestions. We have found the culprit! It was the fuel pump! In my grooming van it is mounted nowhere near the generator itself but far and out of sight above the propane tank on the side of the vehicle! The gas tank is in the same area but the guys at Cummins said they had to drop the propane tank down to access it. No wonder we didn't find it on our adventures under the vehicle.

I've got a PDF of the parts manual and it is called a Remote Fuel Pump! That should have been a clue it wouldn't be near the generator..

Anyway we are happily back up and running! Thanks again, everyone, for taking the time to point us in the right direction. Total down time was only about 24 hours.