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Can't get spark after warms up

jwrape

Registered
Model#6.5NH-3CR/16020P Serial#K833725670

My Onan MCCK Genset has been giving me problems since last season.
Anyways, I have troubleshot this thing to death.
Symptoms:
Will run perfectly for about 7-10 minutes and then it loses spark.
I let it cool, removed the spark plug and laid it on the head still connected, I turned it over and saw a Gorgeous Strong spark, then it depleted to sparking every other or every 3rd rotation, then down to every once and a while and then nothing. During this experienment I had the Volt meter on the coil voltage input (+12v) and watched the voltage go from +10.86v at good spark, down to +5.4v to +3.84v simotaniously as the spark went away.

It's obvious to me that there is a electronic component that is losing it's value as it heats up in the control box.

Can anyone tell me where to go from there???? I have followed the coil wire into the control box and it just connects to a black post about the size of your pointer finger, then that is wired throughout the box.

Does anyone know of any parts that are known for going bad in the control box or any common failures?

The Control box I am referencing is on the right side of this picture, it's about the size of a show box with a bunch of electronics in it.
http://img.photobucket.com/albums/v177/jwrape/Boat/mime-attachment.jpg

also here is the front of it
 
D

Don Smith

Guest
Check the gap on the points. Sometimes if it is set to close it will remain closed after the engine comes up to temprature through metal expansion. Also possible that the capacitor might be failing when hot. Don
 

jwrape

Registered
No points anymore. it has electronic ignition.
I can hot wire it to run by bypassing the control box and supplying +12v to the coil and it will run.
It's something in the control box
 

BTPost

Moderator
Staff member
Age
70
Last Subscription Date
12/29/2008
First of all, are you talking about the NH that you gave the Model and Serial Number for in the original post, OR are you talking an actual MCCK Marinized CCK Genset?????? There is a BIG difference between the two....
 

jwrape

Registered
:rant:I feel SO STUPID.... I got it running. I changed the oil and soon realized that it was low on oil.
I had been looking at the dip stick low mark thinking it was the full mark. My lighting is so dark down there that I couldn't see. i feel like such a dummy. :rant: :rant:
 

Billy J Shafer

Subscriber
Age
69
Last Subscription Date
09/03/2019
You mean your boat does not have plenty of room and light to work with.:rant: All boats are easy to work on. At least that is what the salesman always tells the customer.:rant::rant:
 

jwrape

Registered
Exactly! Your supposed to be able to go out on your boat after it sits all winter and crank it up and drive away and nothing should need fixing or maintenance EVER...:bonk::D
 

jwrape

Registered
Well......Once again it's doing the same thing.....So it's not the oil pressure........ I re-scheduled the Onan Tech to come out on the 18th.....
I'm getting so fed up with this thing
 

jwrape

Registered
Well I believe we found the issue:::: YEA!!!!!!!

I had the Cummins South technician come out and service my GenSet on Monday at $99/hr...

He starts by saying, "You know every part on this thing is obsolute?"
I said yes but I'm hoping you can tell me what's wrong and I can find the old part on Ebay or something.
SO, he got started and he traced the power from the coil back to it's source and pulled out this little 1.5" x 1.5" card labeled Onan300A734.

He put the test leads on the top resistor 470 ohm resistor and the FLuke meter went all over the place and then went to an open. He tested the other parts ont hat board and they were good. Upon closer look you could see that the resistor had gotten hot and bled around the leads.

So the Tech says you are getting out cheap. Replace this $2 parts and you should be up and running.

So he leaves and says he's only gonna charge me for an hour and a half. Not too bad. Ended up being $243 some how. I guess taxes or something I didn't get a receipt yet.

Anyways, I went to 2 Radio Shacks to try to find the resistor and they said I would have to order it because it was a 2watt resistor and RS only sold up to a 1/2 Watt. So I was driving home to look this up on the internet and order it when I drove by an old TV repair shop. I stopped in and asked him it he had the resistor. Thank the lord he did. He charged me $3 for it and it's a 2% tolerence as opposed to the 5% tolerence that was on the board. I replaced it and now I only need to slip it back in this weekend and it SHOULD start right up, God willing and the creek don't rise.

Now after new resistor

 

jwrape

Registered
Well, I slipped the circuit board in and tried to start it up this weekend and it started but then the spark died again.... SO although I did replace a bad resistor, that wasn't the main issue.
So my Dad came over and played with it and I showed him how I could hot wire it but it still would run weak.
Well I remember someone here telling me that the GenSet should run on one cylinder but on mine it wouldn't run if I disconnected the one plug. :bonk:
So my Dad investigated the far side plug and found that my brand new plug wasn't firing and that was why it was so weak. He replaced the plug with an old one I had and it fired up and ran strong.

We wired the coil straight to the solenoid so that it gets 12v when the ignition is turned on from the control panel or the switch in the wheel house. It works like it should although it is essentially hot wired.:D Hey you do what you got to do to make it work....

At this point I don't care if we are bypassingt he control panel I am just happy it runs and produces power. We used it all day on Sunday.
 

BTPost

Moderator
Staff member
Age
70
Last Subscription Date
12/29/2008
Wired that way, you have NO Low Oil Pressure Protection... good way to burn up the engine....
 

Major Tom

Registered
BTPOST is correct. You now run the risk of burning out the motor due to low oil pressure. If I were in your situation I would try to re-introduce the low oil pressue switch back into the ignition circuit. Its a simple single pole switch--shouldn't be that hard. This way if you do lose oil pressure your engine will be protected and if the low oil pressure switch is defective (which I think is a good possibility) you will find out soon enough.

If it runs continuously with the low oil pressue switch in the circuit you might want to introduce one of high temp limit swithes back in as well. Following this procedure you will continue to gain added protection or identify a faulty switch or an overheat problem. Good result either way.

Best wishes,

Major Tom
 
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