Genny run away....

[Top Shelf]

Well sort of, more like a limp away...I've got a Onan 15k MDL3. It's an '89 and has always been extremely reliable. Aside from oil changes, fuel filters and the occaisional belt adjustment, it's been golden. One thing I always fretted about was the secondary fuel filter change and the Racor R24S. It's always a little cranky after these are changed. Hard to get the air out and once out, I've always had shut down problems, right after the filter changes. But then it would be fine.

Over the 5 years I've had this and aftter the filter changes, I'd always let it run for a 1/2 hour to an hour before I shut it down. And sometimes it would shut all the way down and others it would sorta limp along and I'd have to snuff the air intake to kill it. But after that it'd be golden all year until the dang filter changes again.

Today I changed both the Racor and the secondary engine mounted filter. Got it running nice and smooth and after about a 1/2 hour went to shut it down. Typical, it went to about a 1/3 of normal RPM and just limped along. I finally snuffed it with my hand and a wet suit. Not too smart I know but I couldn't find my 2x4.

I let it sit for another half hour and fired it up. Lit right away and ran fine, went to shut it down and it did the 1/3 speed deal again. This time I had my little 2X4, but I couldn't get the damn thing to snuff out. Finally after about 10 minutes of dorking around and sounding like it's guts were coming out, I shut off the fuel supply and it finally shut down.

Now thinking there's still air in the system and "hey it'll be just fine", I fire it back up. Now the dang thing is running at high RPM. Went up to 300 volt on the meter, this time the shut down SW has no effect on it. So I shut off the fuel again to shut it down. Lick my wounds and leave before I blow something up.

I thought I understood this thing, but after reading the previous thread I can't seem to find a fuel shut down solenoid on the injection pump (and I have no manual). I do see one wire only that goes to the injection pump. Of course I'm wondering if this shut down solenoid has been going bad for a long time or is something else going on.
The high RPM seems to be a new problem. Thoughts? and as always...thanks in advance.

 

[yachtsmanbill]

Starving it for fuel let it run real lean and it took off. Thats not the way diesels work. Its OK for gas units. That happened on the fireboat I was working on. The other engineer always shut the fuel supply off and never tagged it. I went to start it and it took off with 4 busted rods through the block. That was a 4 banger Cummins 50KW 250 volt DC unit. The owner was kinda pissed!
I wonder with that 2x4 if the engine vacuum didnt pull enough air in with the fuel filter leak to keep it running (?) ws

 

[yachtsmanbill]

Use a little artistic license to read this... If you cant read it here, pm me with your email and I'll fire it off to you ws ws

 

[amarinetroubleshooting]

Is it a Stanadyne injection pump? They do funny things if there is air inside.

 

[Nonchalant1]

I'd guess that your fuel solenoid is not closing all the way. To shut it down, try turning off the battery switch to the genny battery power. That kills the power to the fuel solenoid and shuts it down normally. That works on my 15kw MDJF. They do not use their own power for the fuel solenoid. They use battery power.

Doug Shuman

 

[robertm]

I was having all kinds of starting, sporadic running and shut down problems with an MDJF. At the suggestion of a diesel mechanic, I replaced the fuel solenoid (which fell apart when I unbolted it from the engine), and all problems have gone away. The part from the Onan dealer is gold plated, but it sure did the job. Hope this helps. BTW, I have a set of Onan Manuals for the MDJF. If information from them would help you, I will copy them and send them to you.

 

[Top Shelf]

Well here's were I'm at today.....basically it fired right up. Ran at the proper voltage. I ran it for an hour and it shut right down when I hit the stop switch. Did this 2 more times with similar results.

Before I lit it, I really studied it and it is in fact a Stanadyne injection pump. In fact the shut down solenoid is under a 5 or 6 bolt cover on top of the injection pump. One wire on a threaded terminal and ground strap on the other. It's energized when running at 12 to 13 volts.

I'm thinking....and I can't figure how this makes sense, but after the filter changes, I'm grinding on this thing to get it started and just wondering if low battery voltage somehow affects the shut down solenoid. I never leave the on board 12 volt battery (dedicated to the genny) on. This AM I turned it on and let it charge for an hour or so....

I did speak to a guy at RPM about why the dang thing goes to 200 or 300 RPM and just chugs, rather than shutting down. He said this was pretty common on MDL 3's and there was service bulletin about changing some "metering valve" in the injection pump. They either get worn or they went to a different material, but basically on shut down, a tny bit of fuel gets trhough and keeps the dang thing running at 200 to 300 RPM.

Anyway he told me (as mentioned above) air raises hell with this injection pump. He suggested I disconnect the fuel return line and hand prime it using the lever on the transfer pump, before I try cranking it, next time I change filters.

So that's worth a try next time. I really do need the manual for this thing. But really no luck on the web....anyone have a source with the proper model # etc?

Thanks for all the inputs. Much appreciated.

 

[Top Shelf]

Doug, I'm sorry. A key point you made here. Are you saying once this is running, it's not generating it's own 12 volts or at least not providing it to the solenoid? That still comes from the beattery?

So if you had a weak battery, while it's running, say 6 or 8 volts.....the solenoid wouldn't be open all the way or sticking or binding? I wish I had checked the voltage yesterday when it was limping along.....

Thx.

 

[yachtsmanbill]

I think that shut down solenoid is normaly closed, with voltage removed to close for a shut down. If its the "thimble type", it has a rubber seat that can get worn as well. ws

 

[Avenger]

On a Stanadyne pump the soleniod pulls in a metal "flapper" that allows the governor linkage to move to a run position. De-energizing it allows a spring to pull the flapper out to push the linkage (which controls the metering valve) to a shut-down position. These solenoids can also be configured to be energize to shut down. And BTW, that cover has three screws.

Standyne Service Bulletin #458 documents a change in part number of the M/V to correct a no shut-off when hot complaint. It is also true that if the metering valve is worn it will allow fuel to bypass. There's also the very unlikely possiblity that somebody put a standard size metering valve where an oversize one was required.

 

[Top Shelf]

Thanks Guys.....So does the 12 vlt come from the battery only, as implied above? Or once running it gens it's own 12 vlt? If it's from the battery only that could explain a lot of what's going on here.

Also, if I shut the main 12 vlt sw to the genny. This is outbaord the stb main on my boat. will that de-energize the solenoid and cause it to shut down? Theoretically, if I lifted the 12volt lead off the solenoid while the genny is running...that would "close" the solenoid?

Just wondering, cause the dang thing is running and shutting down fine. Bimini this Friday for a week and would prefer not to revisit this one. Thx much!!!!

 

[Avenger]

Well, I can't see your wiring from here, but usually the 12V comes from the battery until the engine starts, then 12V is supplied by the engine's alternator. Switching off the battery while the engine is running usually fries the alternator unless it has a field disconnect. If you don't know for sure, don't try it.

Lifting the wire from the soleniod will "open" the solenoid (if it's energize to run) which would close the metering valve and shut down the engine. Assuming everything is working correctly. I have seen soleniods with a LOT of cycles on them develop a wear spot in the "flapper" which can make them hang up partially open. However I don't think I have ever seen this in a generator application. Unless you're starting and stopping it many times a day every day I wouldn't be too concerned about that.

 

[Top Shelf]

Here's a couple of pix of this injection pump. If anyone has a manual for the MDL 3 and can post the air bleeding or purge procedure after a fuel filter change...I'd be very grateful. Thx.

 

[Nonchalant1]

As I mentioned, my description is how my 15KW MDJF works, so they must be different. My MDJF has no alternator. It starts with 32V from the house bank. Turning off the genny battery switch de-energizes the solenoid and shuts down the genny just fine. If yours is different, don't try it.

Yes, disconnecting the wire to the solenoid will normally stop the engine. However, if your solenoid is not closing all the way if may continue to starve and run. If you do disconnect the wire to the solenoid while it's running, be careful not to let that hot wire touch anywhere. ZZZZZTT!

My MDJF has a shutdown switch on the control panel of the generator and a remote switch at both the helms. Mine exhibited your symptoms previously when the contacts on the remote shutdown switch were not working correctly but I could shut it down at the generator just fine. Since yours is running and working OK for now, maybe don't mess with it until you get back.

I wish I were there where you are, not so I could help, just because I wish I were there.

Doug

 

[Top Shelf]

Thanks Doug....you ever see Top Shelf tied up anywhere come on over for a cold Pop.

Just went to the local marina for a quick 150 gals to top of for the trip. $5.31 a gallon......Didn't need enough for the truck to deliver...man that really bites. $850 for 150 gallons......

Wonder how many trolling motors I'd need bolted to the transom to turn 10 knots....then just run the genny. This is killing me...even at 10 kts....Thx.

 

[bobk]

Two thoughts on dealing with air after fuel filter changes. These worked well on an 8KW in86 model.

1) Use a two micron Racor in front of the engine mounted filter. It is easy to fill to the top after a filter change. Just be patient. Forget changing the engine mounted filter. I didn't see a bit of dirt in the main filters on the Lehman or Onan after 5 years doing it this way.

2) If you have an electric fuel pump, you can prime the engine mounted filter by simply disconnecting the appropriate wire and touching it to the proper battery post.

Bob