Onan Generator stalls after oil/filter change

[dawg6]

[SOLVED] Onan Generator stalls after oil/filter change

Edit: problem solved: long story short it was the secondary fuel filter.

One of my 1987 Onan 20kw generators was working perfectly fine until after my recent oil/filter change (changed oil filter and racor filter). The other generator is working fine after going through the same changes.

It starts fine, runs for about a 30 seconds to a minute then stalls. Sounds like it's being starved for fuel. The fault indicator is not tripped. After it stalls it starts right back up fine, runs for 30 seconds to a minute then stalls again.

What else can I check besides the obvious (checked Racor filter, oil level, good water flow out exhaust while running, and everything looks fine)? I'm hesitant to pull the on-engine fuel filter just yet, because so far I haven't done anything that would require bleeding the fuel lines and I have no reason to suspect it suddenly went bad or got clogged, although I suppose it is a possibility.

 

[Pascal]

If it doesn’t shut down suddenly tripping the fault breaker it would usually be fuel but then it wouldn’t fire right back up without priming. But if it s not shutting down on a fault then it would not be a sensor.

I had an odd issue on one of our 2004 47kws. If shut down once for no reason 2 weeks ago. Then ran fine for a a week or so. When we got back to Miami it started shutting down after a few minutes and sometimes would not restart. Both me and my very good gen specialist thought it was fuel until he put a voltmeter on the engine controls terminals to check voltage. As he was pushing down, the gen fired up right away. Turned out to be a problem on the controller circuit board. Replaced with a spare and all good. When I opened the box, I found some dark spots on the board.

Don’t know if yours use a similar controller but worth a look. Maybe you bumped the wires during the oil change? On ours the controller send a signal to the fuel control solenoid on the injection pump

 

[Captain Ralph]

Is this the big OhNo 20 with Cummins MD4?

 

[Pascal]

Is this the big OhNo 20 with Cummins MD4?

You tahlkin’ to me? . Yes, Cummins 4BT

 

[Captain Ralph]

You tahlkin’ to me? . Yes, Cummins 4BT

Sorry, was asking the OP on the problem gen-set.
What model?
With box looking secondary fuel filter and diaphragm lift pump.
Electric run wire to the rotary Stanadyne injector pump?
If that model, look over well the 3 items I just mentioned.

 

[dawg6]

Sorry, was asking the OP on the problem gen-set.
What model?
With box looking secondary fuel filter and diaphragm lift pump.
Electric run wire to the rotary Stanadyne injector pump?
If that model, look over well the 3 items I just mentioned.

It's the Onan MDL4. Yeah I looked over everything and it appears fine externally. No wires disconnected or any indication that something is burned or anything like that. Also checked the circuit board area and didn't see any scorching or anything like Pascal suggested.

 

[Captain Ralph]

It's the Onan MDL4. Yeah I looked over everything and it appears fine externally. No wires disconnected or any indication that something is burned or anything like that. Also checked the circuit board area and didn't see any scorching or anything like Pascal suggested.

The wire that goes to the injector pump, ensure it is tight. Follow that wire. I recall it connects again close to the mini load cells between the head and generator with some other wires. Check those connects also. This wire has caused our customers problems before. It gets bumped during service.
After that, you need to test all the shut down sensors. After 34-35 years, they may be giving you issues.
Do you have a working mechanical oil pressure gauge on the engine? Showing good pressure?

 

[dawg6]

My oil pressure guage does not work (hasn't since I got the boat), but I believe the one at the helm does. I will check that tomorrow along with the wire as you suggest. I'll also reserach how to check the sensors to see if they are actually working.

 

[Pascal]

Sensors are often the prime suspects but again it would trip the fault breaker.

Check if yours has a fuse in the harness bringing power to the controller, above the flywheel. Our 45s do, one of the fuse holders has been replaced in the past.

 

[dawg6]

I checked the oil pressure guage at helm and confirmed oil pressure does go up when it's running.

I believe there are two oil pressure sensors, one on top of the filter with 2 wires that I assume goes to the guage in the helm. The other, with one wire, is below the (broken) guage mounted on the engine, next to the dip stick. I tested it and it appears to be working (checked continuity between the wire terminal and the sensor body; it is closed when off and open when running).

I only found 2 fuses. One next to the starter (assume it's for the starter) and one in the control box, which someone wrote next to it "12v guages", so I assume is for the helm guages.

I found two sensors on the back which I assume are for the coolant. One has one wire and one has two wires. The one with one wire is reading open when the engine is off as well as while running (checked continuity between the wire terminal and sensor body). Could this be the issue? Shouldn't the fault trip if that's the case? Or maybe I am checking the sensor incorrectly? Normally, my temp guage in the helm works fine, but of course I can't keep it running long enouh to get the water temp to increase right now.

Here is the one with one wire. In the parts manual I think this is the "Sender Water Temperature."


Here is the one with two wires (photo is from underneath, looking up). In the parts manual, I think this is the "Sender, Low Coolant Level"


Also, it looks like a previous owner replaced the fuel pump with a 12v pump. It doesn't have any kind of priming lever. Does this mean I don't need to prime the system if I change the on-engine fuel filter? Or do I still need to loosen the fuel line at the injector, crank the engine over until fuel comes out and then tighten the fuel line?

Here is the fuel pump:

 

[dawg6]

Just realized there are two more oil pressure sensors, on the engine body. Will check those next.

 

[dawg6]

According the parts manual, for the other two oil pressure sensors, one is supposed to close at 14 lbs decreasing, and it is open while engine is off and while running, which I assume is correct. The other is supposed to close at 5 lbs increasing and it is open while off and closed while running, which I assume is also correct.

 

[Pascal]

Again different models but on ours the mechanical fuel pump is before the secondary. If that s the case you could loosen up the fuel line exiting the filter, power up the pump to make sure fuel is coming out.

Not sure how an electric pump will work on a gen without a preheat button. With a preheat or run switch the pump kicks in so you can prime. If your Onan only has a start position you can’t use it to bleed.

 

[dawg6]

According to the owner's manual, I should hold the start/stop button in the stop position for about 10 seconds to pre-heat the engine. Not sure if that also activates the electrical fuel pump or not.

I guess I can change fuel filter to find out. I was hoping to avoid that until last resort (since after that, if it stalls out I won't know if the engine is primed or not). But I think I've checked everything else it could possibly be. It sure sounds like a fuel problem: maybe fuel filter is clogged or the fuel pump is failing. Either way, I guess I'm at the point where I need to take that filter off.

 

[Pascal]

I change the secondaries (and primaries) at every oil change. always.

The pump should be wired to the preheat circuit. Easy to check. Press the stop switch and hear/feel the pump

 

[northshoreone]

Does it have a overheat sensor? My 1996 20k did and it was bad, doing the same thing yours is doing. Simple fix if that’s what it is.

 

[northshoreone]

If I remember correctly it was the two wire sensor in your pic

 

[dawg6]

Well, I guess the simplest solution really was the right solution. Replaced the secondary filter and now it purrs like a kitten again. Maybe when I changed the Racor filter some debris got dislodged and stuck in the secondary.

BTW, the off button didn't engage the fuel pump. It only turned on when I held the start button. When the engine stalled I could even hear the fuel pump "clicking" until I pressed off (now I know what the clicking sound was).

Anyway, I like the advice of always changing both when I do oil changes. Will add that to my check list from now on.

Time to go change the one on the other generator as well and order some more spares.

Thanks everyone! In the process I learned a lot more about my generator and troubleshooting.

 

[Pascal]

Glad you got it! A little odd that the dirty secondary would shut down the genny so quickly with no load but... it s a boat!!

 

[Westfield 11]

Do both fuel filters really need to be changed every 100hrs? IIRC, that’s the oil change interval for the MDL4 of that vintage…..