Generator Problem

[astmi]

My generator is an Onan 7.5kw diesel. It runs for a minute or 2, then stops. The load at start is between 15-20 amps and reduces gradually to 7-8 amps. This load situation does not appear when connected to shore power. There is no fuel.

Any idea on the possible cause of this problem.

[wolfe10]

Sorry, need a better description:

No fuel and the generator should not start.

And as to affect of being connected to shore power-- most coaches are wired so that the generator is the "favored" source so if generator is started, the load transfers from shore power to generator. BUT, the ATS (Automatic Transfer Switch) could be wired so that shore power is the favored source. You can NOT have two sources of 120 VAC power at the same time.

If you do have fuel (over 1/2 tank), turn off your main breaker in the 120 VAC breaker box. That will prevent a heavy start up load. See if the generator stays running.

If not, check oil level, check for fault codes.

[RVerOnTheMove]

In case did not make it clear, the generator will shut down if you are low on oil and is likely the most common reason for a generator starting and then quiting. When power sourced are changed some things like your 3-stage battery charger will start over with a bulk charge, find it's not necessary and drop to a lower level and then finally to the float (not sure of the correct terms). If everything is working properly, this should also happen if you were on shore power and the batteries were fully charged. Disconnect and reconnect your shore power and you should see the same brief amp increase followed by a gradual drop.

[bm02tj]

Also, a plugged air filter can cause a shut down check flash code at the control.

[astmi]

Shore power is not connected while I try to run the gene.

There are no fault codes.

Oil level is OK and fuel is full.

I wrote that the amp meter shows à 15-20 amps load when thé gene runs and reduces rapidly.

This load does not occur when I plug the RV to shore power (gene off).

I triied to run thé gene with the switch at off position. Same problem.

Could there be any electronic device that would stop thé gene?

[tbutler]

We had a similar problem with our generator, also a 7.5 KW, this summer. We would get weird voltage and amperage readings and then it would shut down. It turned out to be a loose ground wire in the generator to coach connection. It had shorted and melted a bunch of stuff. We had Cummins/Onan replace the wiring harness from the generator to the link to the coach. Everything repaired, the generator works fine. The mechanic who found the problem said the set screw which should have been holding the ground wire in place was completely missing. It must have vibrated loose and fallen out which eventually happened also to the ground wire. If you want to check yours yourself, the cover for this box has a stern warning about high voltage, not to be ignored. Our was located on the front of the generator on the left side as you face the generator. You will see the wiring harness of the coach entering at the same location. Removing the cover will allow you to see the wiring. On ours the damage was apparent once the cover was removed.

[astmi]

Thanks

I'll check that

[astmi]

Mechanic changed the fuel and air filters. It seems that the gene could run.

But, when I push on the start button to start the gene, the starter goes on immediately, no delay for priming or for the glow plugs to warm up. I have to hold the starter on too long for the gene to start.

Nô body found the cause of the problem

Any idea?

[kingofmonaco]

I had a problem with my 7.5 Onan. It would run for a bit with no load on it then shut down. It was hard to start and if a load was applied it would run for a bit become erratic RPM wise and shut down.

After trouble shooting found it was starving for fuel. Change fuel filter and it has been working great. Has your fuel filter been changed lately?

[dickandlois]

Astmi, you posted --Mechanic changed the fuel and air filters. It seems that the gene could run.

By could run, do you mean the mechanic got it running? Or did they just change the filters for you?

There should be a delay before your model generator starts to heat up the glow plugs and prime the fuel system. Bad fuel pump? Maybe !

You mentioned that it would run for about 2 minutes, then quit in your first post, I take it that the issue now is it will not start at all.

There are fuses in many of the coach circuits the can fail. Like one in the DC charge wiring from the Alternator and the Generator.

Have you measured the voltage at the batteries when the engine is off? The Reading/

What is the voltage at the batteries when the engine is running? What is the voltage at the batteries when plugged in too shore power.

With out the generator running its not possible to know if they charge when its running yet. The current reading you had when the generator was running could be the charger / inverter running at high charge (normal when it first starts charging) Then the charge rate decreases over time, till the batteries reach there float level.

Got to find my generator service information to see if I can find any information on where and how the start delay circuit works. That is a new one for me.

This is the information that covers what most owners can do or have checked before repair center intervention.

ENGINE CRANKS BUT DOES NOT START

(Fuel delivery, glow plugs or engine are marginal)

Corrective Action:

1. Check fuel level. (Note: The genset fuel pickup is probably higher than the vehicle engine pickup.)

2. Prime the engine fuel system.

3. Check the engine air filter and remove any blockage. You mentioned that the fuel and air filters where replaced !

4. Replace Fuse F3 (glow plugs) if blown. If it blows again, go to Step 8. This step is not listed as it requires removal of the generator cover panels,best performed at a service center. Fuse is located under the circuit beaker panel.

5. Check for fuel and air leaks at each fitting in the fuel supply line. (Note: White smoke indicates air

in the fuel.)

6. Conduct a fuel flow test and service as necessary.

There are a number of other service steps, but they require removal of the generator cover panels.

7. The other personal addition to check is the Oil pressure sender, this should set a code in the control module. Should this be the case you will need to have the engine serviced at a repair shop.

Rich.