Microquiet 4000 Shutting off

Hello Friends

Bought a 2001 Winnebago Brave 34T 4 months ago.in Very low milage and in great condition. My only problem is the generator. It's a Onan Microquiet 4000. 4Ky. Rear mounted splash lubed with under 400 hours on the clock. Recently serviced and runs like a top when it runs. Here is my problem.....

At about 75% or higher load in an 85F outside temp or higher, the generator shuts down and will immediately restart without hesitation. The shutdowns are consistent with engaging the stop button. No sputtering or warning signs just shuts down and free spins to a stop. Starts right back up and will continue to run under a light load but once the load  is back to 75%, it will shutdown again. I have isolated all remote controls from the generator and it still shuts down. I am down to the units factory components at the generator. I have removed the start/stop switch from the generator and it meters good and feels good. I will test  the generator this weekend with the switch out if the circuit. I have reviewed the wiring diagram and cannot identify a thermal cutoff switch anywhere. I have read that there is one but have not seen any evidence of its existence. I am reasonably certain that the shutdowns are thermally induced either by design or by a fault somewhere or both. I have noticed that when I am driving with the generator running under similar load that the generator seems to be a little bit more dependable maybe due to the fact that battery charging duty is switched to the coach engine reducing the load to the generator which in turn reduces heat. Air flow might be a factor also. Speaking of airflow... The airflow from the generator cooling fan is working great. All is clean and serviced

Any help would be appreciated

Thanks

HJF

There may be a lever to control air flow for cold weather. When in the cold it preheats the intake air.

Fuel pump

Propane or gas fuel?

Its gas. I tend to lean away from the fuel pump because of the manner in which it shuts down. It just stops as if the stop switch was pushed. It doesn't reduce in power or surge in rpm. Just cuts out like a stop switch. Could I be wrong leaning away from a fuel problem?

FYI... Today I will be testing the unit under 75% load with the generator mounted  start/stop switch removed from the circuit. We are currently on shore power but heading out today in 90F heat. I have previously eliminated both remote start/stop switches. Also.... The shutdowns have never resulted in a fault code.

The preheat circuit could be malfunctioning but the question of how the unit is shutting down, remains unclear. The unit runs beautifully when it runs and will run endlessly under smaller loads or large loads in temps under 85F or about.

The unit has never tripped the main breaker at the generator and never has a breaker in the coach tripped. Everything in the coach Weeks perfect with shore power. Never a problem.

Your mileage may vary, but my Gold Marquis 5500 stopped in the manner you describe when the fuel pump went bad. At first it had to warm up before stopping but it became more unpredictable.

Next time it stops I'd pull the fuel line and run the pump into a bottle to check the flow. If that looks good I'd check the pressure.

Both on my genny are much easier than what you've been doing.

Good luck,
Tom

Thanks Tom I Will check  that although because the unit immediately fires back up without hesitation, the pump must be pumping fuel. I say immediately but in actual time I mean less than 10 seconds every time and its happend at least 12 times. It restarts quickly and with the same number if cranks as any other start.

Well you're probably right.

Henry -  If you do not have the service manual for your Onan, PM me a good email address and I will get it to you via a PDF file.  One manual I have is for Spec J thru L and the other is pre-Spec J...... the spec being the last character in the alpha-numeric model number on your nameplate.  I didn't see anything in the troubleshooting guide(s) that fit your exact condition, however.

My genny acted like a lot like the descriptions others have given in the past; i.e., it would run for 20 minutes or so then abruptly quit.....no sputtering, no nuthin' ..... like something had cut a switch off.  Unfortunately, I never tried to restart mine right away, but doubt it would have started (like yours does.)  In my case, a new fuel pump and filter cured that problem.  Those little electric fuel pumps are weird critters, methinks......odd failure modes. 

Be sure to let us know the resolution to your problem.  All of us like to add to our knowledge/experience base (cuz we know we may be next.)

Safe travels.................... ed s

  The two times my Onan ( mines an old 7k) acted like yours, it was the fuel pump. Symptoms will worsen if it?s the pump. The first time I had the problem I couldn?t believe it was the pump and screwed around fiddling with everything else until the pump finally wouldn?t let the engine carry hardly any load at all to speak of. The second time, the first thing I did was change the pump and throw an extra one in the tool box.
  I have a theory as to why they will die abruptly, then immediately restart at the beginning of pump failure. The pump is dying as it get hotter, but putting out enough fuel to carry load.  Then the load increases ( on mine it would usually be the second ac compressor kicking in) governor opens for more fuel, it?s not there and engine dies immediately because it?s fixed ignition timing and no way to lighten load immediately. But, while it was dying pump was still pumping a little  while generator turns to a stop and oil pressure falls to cutoff switch level leaving enough gas in carb for restart. The pump gets to cool for a minute or so and is ready to start up and run again for a while.
  I don?t know if any of this is true or not, but that?s the way I explained it to myself. I?d be interested in other opinions.
  Your problem may be something else, but I seen other posts on here where no one could believe it was the fuel pump until they changed the fuel pump. My fuel pumps died at 380 hours and 790 hours in very hot weather.
    Also, if it?s a fuel problem and it dies with no load or light load on engine, it will take a minute of sputtering and popping to die.
 

Update.... Left shore power noon time yesterday. Outside temp hung at 81F. We parked at 2pm and fired up the generator with the main start/stop switch removed from  the unit. a/c on and fan on high. Ran for 2 hours perfectly. I then decided to increase the load by switching the fridge from gas to a/c. Within 10 minutes the unit shutdown. This time I pushed the start button immediately following the end of the engine free fall to stop. Started immediately. Switched the fridge back to gas, turned the a/c back on to high and it ran flawlessly for the remainder of the days usage. This officially eliminates all of the start/stop switches.

Ed, I did get a copy of the service manual yesterday (J-N). Mine is a J. There is a troubleshooting condition in there that is a shutdown with no fault code which is my circumstances. On Thursday I spoke with cummins and was relayed that section which suggests a bad start/stop switch. That diagnosis is officially proven wrong.

Jubileee, your info is very interesting. As Tom previously suggested, check the fuel system. More specifically the fuel pump. The conditions you experienced are very much the same as mine in that it shuts down with zero hiccups. Tom suggested to remove the fuel line and check for flow and pressure. I can check for flow but dont have the means to check pressure at the moment. I do think that I have received enough info now to look at a fuel problem. I did previously drop the bowl to clean and check. It had normal particles in the bowl, I cleaned it out and reassembled. I also noticed that the previous owner broke off the altitude needle adjustment knob which I found in the cabin but didnt know what it was until I cleaned the bowl. Based on my internal view of the needle and the alignment of the broken off knob, I concluded that it is set within a reasonable position based on my current altitude. The other thing I will do today is replace the fuel filter. I picked one up last week and will install today. If the filter is restricting the flow, it could put extra stress on the pump which could lead to excessive heat at high demands. Take care of that today.

Thats the update for this morning. Thanks to all contributing here. Its a big help and hopefully when complete, it will be of assistance to others.

Henry

One more note..... Just found a fault code this morning. Fault code 15. This appears to be a loss of proper a/c frequency. Less than 54Hz for 30 continuous seconds. The possible causes are broad but does list fuel supply as a possible cause. This also questions a stop condition which was my original suspicion but seems to be eliminated now. Fuel is looking more likely.

Henry

Henry J Fate said:

....The other thing I will do today is replace the fuel filter. I picked one up last week and will install today. If the filter is restricting the flow, it could put extra stress on the pump which could lead to excessive heat at high demands. Take care of that today....

Click to expand...

I seriously doubt the fuel filter is the root cause of your problem, but always go for the low hanging fruit first. If your generator was diesel, a fuel filter could get slimed up due to biological activity in the fuel - that happens with not enough fuel getting turned over (used, the generator doesn't run enough.) I've never had a small engine problem due to a bad fuel filter.

The idea of a heat induced fuel pump failure sounds completely plausible to me.

Didn't get to change the fuel filter yet. After reviewing the procedure,  I felt it would be best to wait until I get back on shore power. I believe the fuel filter is original and want to be prepared if removal causes any problems.

John. I agree. I think its more likely to be the pump. I did call commins yesterday and was told that the pump has no thermal protection. I believe that to be accurate info. If my calculations are correct, in order to have a drop in frequency to 54Hz, the generator rpms would need to slow 10%. 30 seconds of this would produce fault code 15. I believe thats 3240 rpms from 3600. Very likely this could be going unnoticed. Add some tolerance in there and it could be less of a rpm drop.

Thats about it. We are out on the road  today but will be docked with shore power tomorrow and will resume repairs. First thing in the morning I will try to locate a new pump. We are in south Florida. There are several part house options. Hopefully one of them will have one.

Enjoy the remainder of the weekend

Thanks to all

Henry

Short update.... Got a fault code 14 today. That's a high frequency rate of about 70Hz. The generator shutdown. The fault immediately followed a manual a/c shutdown. I suspect that when I turned the a/c off, the generator was very close to shutting down on a fault code of 15 which is too low of frequency and as we expect, probably lacking enough fuel for the load. The removal of the load sent the generator into a lean spin which in turn spun the generator to fast causing the fault code 14. Sounds good in theory but still unproven. Tomorrow I will have shore  power and will look at the fuel system. The pump is definitely getting the most suspicion. I had a thought about a possible leaky line between the tank and pump. Could it be possible to have a leak in that line sucking air just enough to keep it running under light loads but not bringing in enough fuel at higher loads? The thermal factor does not seem to be something that would worsen that particular problem. Or maybe it could? Who knows. The process continues.

Henry

Found a Cummins supply house with 4 pumps in stock. $64. The local RV rip off shop wanted $165 and they tried to throw in a filter total over $200. They were getting the pump from Cummins too. Mark up of $100. I dont mind making a little money but a nation wide RV dealer and repair shop marking up a $65 part $100?

Installed the fuel filter this morning. No problem removing or installing. Checked the fuel supply lines for any sign of a problem. All looking fine. One section Needed some hanger work which I took care of but all looked good. Fired the generator up ran great. Switched the load off shore power to generator power. 10 minutes and shutdown fault code 15. It was in the low 90's for the test. A/c running full steam. This time I stood outside by the generator listening and watching. It seemed like it was struggling some but grinding it out. Rpms were a little lower than a no load condition. Cant really say if there was a slow decline in RPM's or not but according to the fault code, it probably did occur. Hopefully I will have the pump tonight. I plan  to install it tomorrow. I am crossing my fingers and hoping for a big surprise. We leave for Tennessee on Wednesday. Lots of stuff to do. This problem is not helping.

Henry

A voltmeter is a reasonable rpm indicator, because the genset has to maintain constant rpms to produce 120v. Usually 3600 rpms for a gas genset, but check your Onan spec. If the voltage regulator/speed-governor can't maintain the required rpms, the voltage falls.

Note that the above doesn't apply to inverter-type gensets (they re variable speed), but the Onan 4000 is not one of those.

Update..... Fuel pump arriving tonight. Will try to install before heading north tomorrow.

Gary, didn't think to hook up my volt meter to check voltage. I suspect that you are correct that voltage would suffer if rpm decrease. If I could assure a reasonably constant load that eventually results in a code 15, I should be able to notice a decline in the voltage during the generator's failed flight. That could help to validate the fault code 15. My only question is...... If the generator is chugging along at 60Hz (3600rpm) @ 120 volts and then suddenly drops to 3240 rpm, what would be the voltage response? I used the 3240 rpm because that would be the nominal threshold for a fault code 15 shutdown.

Henry

Update.... Got the fuel pump. $63 from commins. Will not be able to install today. Will install out on the road.

Gary, I did some service manual research. The controller monitors the output voltage and electronically adjusts the voltage when needed. The service manual doesn't offer any info about frequency. I believe that frequency is a product of motor rpm and that there probably is not any electronics to compensate. My opinion is that voltage would not reliability indicate a change in rpm however there could be a voltage response that is consistent with the controller making adjustments for changes of load.

The rpm of the unit appears to be a product of the governor. This would be a mechanical adjustment to variances in motor speed caused in most cases by a load switching in or out. The governor is always trying to bring the motor back to its set point which in this case is approx 3600 rpm. There are some variances in the functionality but its designed to keep the rpm in a safe zone for operating 60Hz appliances. The two fault codes associated with rpm are codes 14 and 15. I assume this monitoring is separate from voltage monitoring. Its possible the controller could be using voltage as a guide for rpm but that could lead to inaccurate troubleshooting. Hz or cycles are probably separately monitored.

Because the governor is responsible for keeping the rpm at approx 3600 rpm, a failure of rpm could be a failure of the Governor or more likely the Governor is asking for more rpm but the engine isn't responding. Fuel would be a cause of this. I am keeping my fingers crossed. Not sure when I will be able to replace the pump. I am guessing that I will get to it in Tennessee on Friday or Saturday.

Thats all for now

Henry