Onan 21.5MDKAE need ideas

[GCSI]

The generator is still giving me fits, history so far

Ran for 5 day stretch 24/7, no issues.

On final 30 minutes of day Five unit died.

- Discovers large chunk of smutz clogging ball area of Racor.
- Installed new kit in Racor.
- New Racor filter
- New secondary Onan fuel filter
- Discoverd fuel pump very weak
- Installed new fuel pump; discovered fuel line from tank had obstruction.
- Blew low pressure into fuel line, cleared obstruction
- Fuel is now making consistent fuel flow at outlet of pump.

Unit will run for five minutes, then shut down.
Water pump cover plate is cool to touch, impeller is intact; I’ve not changed impeller, yet…

Any ideas???

Using aux generator, so not dead in the water

Brett

 

[Pascal]

I d check coolant temperature to make sure it doesn’t shut down on overheating

It sounds like fuel related. Do you have priming pumps? Try leaving the pump on.

I had a similar issue last spring with one of the Onan 47s on the 116. It was the fuel pump. It would run forever or no or low load but would stop right away on heavy load. What was tricky is that usually when a gen isn’t getting enough fuel it usually hunts and then shuts down gradually. Turns out some onans will shut down voltage or freq drops below a certain level. Running with the priming up helped.

I know you ve replaced the fuel pump but it s worth trying running with the priming pump to see what happens

 

[GCSI]

Pascal: No priming pump. I can put a hand on the engine without burning, so don’t “think” it’s overheating. I just pulled a perfectly good impeller, will replace then shoot engine w IR Thermometer.
It’s behaving like fuel starvation. I’m wondering if the fuel pump relay is wonky? Will rig up some test leads to check voltage while running after I wrestle with the new impeller….

 

[Steve Mannshardt]

Any chance the fuel tank vent is also restricted with gunk?

 

[GCSI]

New impeller installed, ran for a few minutes and died. Interestingly the shutdown solenoid is triggering the stop after unit starts to loose rpm’s.
Shot thermostat housing w IR Gun (160*). I’m out of ideas

 

[Pascal]

Pascal: No priming pump. I can put a hand on the engine without burning, so don’t “think” it’s overheating. I just pulled a perfectly good impeller, will replace then shoot engine w IR Thermometer.
It’s behaving like fuel starvation. I’m wondering if the fuel pump relay is wonky? Will rig up some test leads to check voltage while running after I wrestle with the new impeller….

Check the wiring and control circuit. I also had an issue with an inline fuse on our 47KW which would sometimes shut down or not start. Also with a loose solder on one of the control boards.

 

[Captain Ralph]

Sounds like a fuel issue but I remember my asp was kicked once;
Some later Oh-No's have a raw water pressure valve after the raw water pump. In the hose after the pump, a short tube nipple with sender and 2 wires.
From the manual;

 

[GCSI]

I’m ready to throw in the towel. Presently located Spanish Wells, any options other than return Miami for service. Been messing about for better part of all day….

 

[GCSI]

Ralph: Is it possible to determine which CB Fault occurred?

 

[Captain Ralph]

What happens if you hold the start switch in (other than making a bunch of starter chatter)?

Next, when the gen-set comes up, do you see ANY ACv trying to ramp up?

Your second gen-set enough to make your vacation work?

 

[GCSI]

Ralph:

If you hold started in after failure? Starter turns over engine, won’t run.

Develops power while running

Second gen set will carry most loads. We had planned on remaining Bahamas till mid springtime periodically venturing south using SW as launching point.
Will probably try to head to Fl for service after New Years

 

[Addie-Kat]

I just had a problem with my 20kw onan. Would start and run, then surge and die. Had my mechanic look at it and found a hairline crack in the racor bowl, not enough to leak fuel, but just enough to suck air. Took awhile to get the air out of the system, but the engine fired up and is now purring like a kitten. Yours could be getting air locked.

 

[Captain Ralph]

So, your not doing anything to the fuel system, pre-heat for 10 to 15 seconds, hit starter, it starts rite up and dies.
At this time Vac is starting to ramp up.
Then, it is dead, repeat same above again and hold starter button; starts rite up and dies but starter turns it over only.

Your model gen-set may have an exposed run solenoid to governor control rod.
Hold that rod in the run position while you start it up. If you can hold that rod and it keeps running, we know there is a fault shutting it down.
If it dies with that rod held in the run position, it's fuel.

You did use new O rings on the Racor? Oiled the new lil orange O ring when assembled?

If you have already checked the connects to the exhaust riser, water temp and oil pressure senders and it keeps running holding that rod, a electrical issue/fault (false?) is proven.

There are 6 relays. 2 run the run solenoid at different times.
All of these relays are the same.

 

[carolinacoast]

likely redundant....fuel lines still all clear, and supply side pulling air somehow that lowers fuel pressure? gasket on racor? could tank pickup have gotten debris back in it? pull secondary out, and 2 micron in racor and see if different? Spanish wells beats where most of us are.

 

[GCSI]

Ralph:

Starts normally, runs for three to five minutes developing power then starts loosing RPMs and dies.

If, after dying I engage starter, unit cranks but won’t start. At this point of sequence, I remove fuel line after fuel pump and hit
Pre-heat toggle the fuel pump is making strong flow.

I “think” I physically held start plunger and unit still dies, will confirm this morning.

So….. it’s sounding like a fuel issue. Could it be the fuel pump is loosing power?

 

[GCSI]

Latest news:

Was able to stretch Racor fuel supply hose to adjacent gen Racor (separate system and fuel tank, that gen runs perfectly)
problem still occurs after three minutes run time. Problem is NOT related to Racors.

Engine stumbles and shuts down even if plunger is held.

Is it possible to jumper fuel pump power supply within control box such that pump will run continuously? I’m thinking all indicators point towards intermittent fuel pump. Other thought is collapsing supply hose, however, think it unlikely due to such a low vacuum/ flow rate.

 

[Pascal]

For testing Probably easier to temporarily power the pump directly from a 12 V source

 

[Fanfare]

Spanish Wells, with its large lobstering fleet, has an enormous knowledge base for diesels. And all the mechanics are now home for the holidays--you just have to find them. Inquire at the boatyard and at the powerplant for names. Ask a few of the Devil's Backbone guides because they know everyone. (Tell them Hi from Fanfare!)

Before heading back to the States try Nassau.

Fanfare only has one generator yet we have gone months running it continuously--not that I didn't always worry, but it is what it is. I did eventually dump our Onan for a Phasor. I would not ruin my trip over the generator if it meets most of your requirements. Should it finally fail you can return home by plugging in at marinas on the way. Overnight keeps the fridge frozen. SW, Nassau, Chub, Cat Cay, Florida. Even if they are full dockmasters will find a place for overnight once you explain your problem.

Good luck, enjoy the Bahamas.

 

[GCSI]

Connected fuel pump to continuous 12V…….. Same symptoms. Now I’m really stumped

 

[Bob Quinn]

might be worth trying to run out of a fuel can, bypass all the stuff between the gen and the fuel tank. It might help to narrow down the issue.
Had a similar "would run for 5 minutes" issue with one of my DD 8v71's. It took months to find the issues. One small leak at the fuel pressure sensor and one small leak at a fuel line joint near a racor. So small they were hard to detect except for a small amount of dampness at the leak.

Same symptom though. I would re-prime the system and it would run 5 to 7 minutes then stall from air getting sucked in.