Onan genset 4.0 no spark. Help

[PigCreations]

Just bought a 84 Winnebago for $300. Runs and drives unbelievably awesome. Onan generator turns over but will not start. No spark at the plugs. I am guessing it is the coil or the ignition relay. The gen is currently out of the motorhome and is in my shop. I hooked up the gen to a fresh battery with jumper cables. Coil tested 14k ohms at the plug wire connection and .003ohms at the neg and pos terminals on the coil. Not sure if that is acceptable as I am a newbie on the resistance (ohm) setting. I have not tested the relay yet but the coil has 0 volts going to it and not sure if it should.
Any help is extremely appreciated. Thanks

 

[DonTom]

What is the model number of the Onan Genny? Is it a single cylinder or dual cylinder model?

-Don- Reno, NV

 

[DonTom]

I just looked at your genny photo. It looks like a two cylinder.

Checking such stuff with an ohmmeter is usually a waste of time.

I would start at the neg of the coil (use positive lead of the voltmeter here) and use a ANALOG voltmeter to ground (neg lead of meter) . Crank and see if the voltage makes the meter jumpy as it should. A 15 volt scale would be best, or as close to 15 as you can get.

Does that old genny use points?

-Don- Reno, NV

 

[Kirk]

It would be helpful to know exactly what model of Onan you have. I did find this copy of an older Onan service manual that may help, but might not be the model you have.
Onan Service Manual NHE-NHEL Gen Sets

 

[PigCreations]

Model# is 4.0BFA 1R / 16020C. Coil is not getting power. The wire that runs from the Coil (positive) to the relay isnt getting any power from the relay. Correct me if I am wrong but the wire should send power to the coil while cranking, correct? Below is picture of my probe on that relay terminal.

 

[Matt_C]

Pig,
The coil+ should be live while cranking. I would love to tell you more, but our BF is several decades older. I do see that they were still using the push rod points arrangement. Most of us gave up and used a Pertronix with the magnet on the flywheel.
Matt

 

[DonTom]

Coil is not getting power. The wire that runs from the Coil (positive) to the relay isnt getting any power from the relay.

In an old system like that, I would expect the 12V to be there anyway, but to be sure, check the coil voltage at the "+" while you crank.

Also, does the relay have volatge on the input contact?

You can try putting your own 12V battery voltage on the "+" of the coil and see what happens. It will then probably start right up when you crank. Disconnect any other wires there on the "+" of the coil just to be safe.

-Don- Reno, NV

 

[Kirk]

Here is a link to the service manual that you need. I recommend that you download a copy. Page 25 addresses testing the ignition coil.

 

[PigCreations]

Today I got a new relay. Still no power to the coil. Jumped 12v to the positive side of the coil, sprayed starting fluid into the carb and still cranks but will not start. Does not even sound like it wants to start. With the new relay still not getting 12v to the coil and jumping 12v to the coil, I am loss as to what it could be. All wires look to be in good condition, not broke, cut, or worn spots causing it to short. And the relays have 12v on the power side also. Thanks Kirk for the link on the service manual. I did download it. Anyone have any thoughts as to what it could be or maybe I overlooked something. Thanks again everyone. Much appreciated.

 

[DonTom]

Jumped 12v to the positive side of the coil,

Did you then check the voltage on the coil? Did the voltage drop a lot or what?

Get a cheap analog voltmeter (digital meters are junk for most troubleshooting) and see if it fluctuates on the coil negative when you crank on the 15 VDC scale. It is not possible to get the high voltage without that fast change in voltage on the coil primary.

-Don- Reno, NV

 

[PigCreations]

DonTom. I jumped 12v to the coil and nothing on my meter while cranking. I still dont understand why the relay is not sending 12v to the coil. I cant read the wiring diagrams from the manual so I sketched out my own wiring diagram of how it is currently wired. The red next to the relay terminals is where I am getting 12v. I have researched these 5 pin relays and some say 85 is ground and others 86 is ground. In the attached pic, coil positive is hooked up to the F2 relay pin 87 which isnt getting 12v at any time. If anyone can make sense of my diagram and find a problem with the wiring would be greatly appreciated!!! Thanks

 

[ChasA]

Pig, where does the -terminal connect,? I think your generator is old enough that it would have points. The way a coil works is as follows: the coil + is always connected to battery, the - terminal is connected to one side of the points the other side of the points is to connected to ground (chassis). When the points close current flows into the coil and voltage builds up and creates a magnetic field. When the points open, the magnetic field collapses and induces a very high voltage into the secondary winding in the coil and the fat coil wire takes it to the spark plug.

From your description, it sounds like you have a problem in the primary side.

 

[Great Horned Owl]

Coil tested 14k ohms at the plug wire connection and .003ohms at the neg and pos terminals on the coil.

Unless you are using a 4 lead precision ohmmeter (very unlikely), 0.003 ohms is essentially a dead short. Just by touching your test leads together you could measure that much, even without taking into account both the meter's accuracy and precision.

Joel

 

[DonTom]

DonTom. I jumped 12v to the coil and nothing on my meter while cranking. I still dont understand why the relay is not sending 12v to the coil. I cant read the wiring diagrams from the manual so I sketched out my own wiring diagram of how it is currently wired. The red next to the relay terminals is where I am getting 12v. I have researched these 5 pin relays and some say 85 is ground and others 86 is ground. In the attached pic, coil positive is hooked up to the F2 relay pin 87 which isnt getting 12v at any time. If anyone can make sense of my diagram and find a problem with the wiring would be greatly appreciated!!! Thanks

85 and 86 is the relay coil.
30 is the common contact.
87A is the normally closed contact.
87 is the normally open contact.

See here. What is your voltage on pin 30 of those two relays?

-Don- Reno, NV

 

[PigCreations]

Forgot to sketch in the points but the negative side of coil is connected to the points. Thanks for the explanation. I am getting about 12.5v to both 30 pins. Did some research on relays and the starter solenoid tonight and it seems like some of the wiring is wrong. Correct me if I am wrong please.
1. There needs to be a ground wire on one of the terminals on the front of the starter solenoid. Although the starter cranks with the current wiring.
2. On pins 85 and 86, one needs ground and the other needs 12v to close the circuit to allow power to pin 87 from pin 30.
3. Not sure if the oil sensor is wired to the correct pin.

Thanks for all the input.

 

[PigCreations]

Great horned Owl.
I am sure my meter isn't very accurate either. I am gonna order a new coil and hopefully get it going after I figure out this wiring. Thanks

 

[namumac1]

What about the points and condenser?

 

[PigCreations]

Points looked good but didnt check the condenser. I got frustrated with it so I sent it to someone to fix it for me. I will post the results when I find out.

 

[PigCreations]

Got the gen back. He got it running but says the wires on the stator get really hot and said there is a short somewhere. Guess I will be tracking down a short tomorrow.

 

[DonTom]

He got it running but says the wires on the stator get really hot and said there is a short somewhere.

It could be the stator itself. First, try running it without anything connected and see if the stator still gets too hot.

-Don- Reno, NV