Community Forums

goferfam · 09-09-2010, 02:00 PM

Help needed
2000 Alpine coach with 7.5 Onan Diesel Generator. The generator won't start when its cold, when air temp warms or it has been running it will start up straight away. Has anyone got any suggestions on how to fix this problem. Removed gen top cover, 12volt coming from switch, pulled the glow plugs-OK. Some suggested that it could be the board, but cannot get at it. Front cap need to be removed ? . Oil & water levels are OK.
Salmon fishing.

jacmat · 09-09-2010, 02:03 PM

I think you probably have a problem with the glow plugs.

goferfam · 09-09-2010, 02:19 PM

Pulled the glowplugs out and tested them with 12 volt, they all get hot.

Good man · 09-09-2010, 02:27 PM

Quote:

Originally Posted by goferfam

Pulled the glowplugs out and tested them with 12 volt, they all get hot.

goferfam,
An old glow-plug trick in cold weather is to "cycle" the glow plugs 2 or 3 times back to back before following-through with the cranking.
It builds heat in the cylinder to a higher level on each successive cycle and improves the environment for the pressure combustion to occur.
Try it, let us know what happens.
Good luck,
Jim

goferfam · 09-09-2010, 02:53 PM

Thanks for the reply
At 60 degrees it want start, it blows white smoke but eventually it will start after cranking for a long period.

Good man · 09-09-2010, 03:42 PM

Quote:

Originally Posted by goferfam

Thanks for the reply
At 60 degrees it want start, it blows white smoke but eventually it will start after cranking for a long period.

Goferfam,
Let me be sure I understand what you just stated... (Communication is always a problem!)

Are you saying that it is NOW 60 degrees and that you just attempted to start your genset by turning it "ON" to the point the glow plugs were heating, then repeated that "cycle" of heating the glow plugs two more times BEFORE following through with "CRANKING" the engine to get it running? ...OR...

Are you simply stating that at any time when it is 60 degrees it takes a long time to crank the genset and it blows white smoke (uncombusted diesel) for awhile after it starts?

Sorry to beat you over the head, but you are the "eyes and ears" and we know only what you tell us.

What I want you to do is to raise the temperature in the cylinders by "successively" heating up the glow plugs 3 times... building more heat each time BEFORE you follow-through with cranking.

What I DO NOT want you to do is to just crank and crank and crank continuously... that will not "cycle" the glow plugs to build up heat.

Come back and let me know what you are doing.
Thanks,
Jim

goferfam · 09-09-2010, 04:55 PM

If it is 60 degrees or below it want start, or it starts after cranking it for an extended period. I can't test it at the moment as it is above 60 degrees but tomorrow morning when it is cold, i will try the cycling before cranking . It blows white smoke when it cranks and want start, once it is running it clears up.
Thank you

Good man · 09-09-2010, 05:03 PM

Quote:

Originally Posted by goferfam

If it is 60 degrees or below it want start, or it starts after cranking it for an extended period. I can't test it at the moment as it is above 60 degrees but tomorrow morning when it is cold, i will try the cycling before cranking . It blows white smoke when it cranks and want start, once it is running it clears up.
Thank you

Great!, goferfam,
I will check back with this thread to see if I can assist you.
Good luck,
Jim

takepride · 09-09-2010, 11:10 PM

Gofer:

By cycling it, do you mean you are pressing the "OFF" switch for 5-10 seconds before then pressing the "ON"? Holding the "OFF" side primes the genset to start easier. I have tried it when cold, works well.

Old Scout · 09-10-2010, 08:29 AM

I dont have my Onan operater's manual handy but according to the install/spec work sheet, there is a 25 amp glow plug fuse somewhere on the unit. Since glow plugs are generally pretty hardy beasts [doubt all 3 went bad at same time?], its possible that 25 amp fuse on your unit has blown--does beg the question why it blew but you can pursue that once you find/confirm status of the fuse.

Again I dont have the ops manual handy but as I recall, holding down the start/stop button in the off position clears any defaults and runs the fuel pump to clear air in the fuel lines [but not sure this "primes" a diesel]. "Assume" holding button down in the start position activates the fuel pump and glow plugs. The switch will blink for several seconds prior to starting--not sure what determines the number of seconds or signals when the starter engages. Again, assuming the glow plugs are functioning, holding the start button down for several cycles might increase cylinder temps but continuously cranking the engine is probably not a good idea.

Its a modest effort to unbolt and remove the top cover of the genset--think most of the genset controls [fuses?] are front/ pass-side corner of genset cabinet. Becareful, the 12v circuits are live.

takepride · 09-10-2010, 10:15 PM

Hmm. I thought priming meant making sure there is adequate fuel and no air (i.e.-priming a water pump is to clear it of air and have enough water to develop the pumping action).

Anyhoos... holding down the "off" side of the switch clears the air in the lines and provides a solid stream of fuel to the engine (whatever that is called). It sounds like if Gofer's will eventually start that at least some of the glow plugs are working.

Gofer's description sounds like my genset if I run the fuel level too low in the main tank and the genset is starved of fuel. After I fill up the tank again, it takes a while for the fuel supply to the genset to be constant. It chokes and spits and sends out white smoke until it finally catches. This also happens when it has been a few weeks since it ran and it's cold outside.

Old Scout · 09-11-2010, 08:09 AM

Sorry, I didnt mean to get hung up on definitions here--"priming" IMHO generally refers to pumping the foot-pedal or pushing the flex bulb on a carberator [ie a lawn mower] to get raw gas into the intake manifold/cylinder. Unless the fuel rail or injection pump is running, you cant get fuel into a diesel--I dont think.

Anyway, back in the old days, before glow plugs, you could crank a diesel engine until the very high compression created enough heat in one or more of the cylinders to get the engine to fire. Copious amounts of white smoke [unburnt diesel] were produces until all cylinders were heated and firing. Suspect this is the case here.

Still think its a glow plug/ fuse issue--the white smoke suggests its getting fuel. Perhaps one of the glow plugs has shorted and blown the 25 amp fuse, or the fuse just blew on its own. Once again, I am only guessing here as this is the first time I've seen this problem addressed on the Alpine forum.

Old Scout · 09-11-2010, 10:32 AM

Did manage to find a single post on the IRV2 forum regarding Onan glow plugs--doesnt clarify the symptoms but does indicate plugs can be changed. Just do a global search on "Onan glow plugs"

takepride · 09-11-2010, 11:35 AM

Thanks Scout!

Being new to diesels, I didn't realize they could fire without an ignition point (like gassers). Being that it is possible, I think you are on the right track. It will be interesting to find out what the problem is.

When mine stumbles (as described above) the amount of smoke is not copious, just some. The stumbling doesn't last long. Usually the second or third 15-second attempt lights it up. And it is always my depriving it of fuel. Your explanation makes sense.