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Hank F.
Hank F., RV tech - emphasis on gensets
Category: RV
Satisfied Customers: 14412
Experience:  RV tech since the beginning of the millenium.
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My Onan LP generator cranks, but wont start. I smell propane.

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My Onan LP generator cranks, but won't start. I smell propane. Is it the coil, regulator? Model #6.5nhm-fa/26115h, sn#f980755715. I tuned it up 15 to 20 hours ago in early spring ie., plugs,oil change and air filter. It seems as if there is no fire when it cranks. On an car engine I'd check the ignition system. I am not familiar with LP equipment,but am a serious do it your selfer guy. I checked the to barrel fuses just above the start switch. Maybe you can help before I have to take the rig to Cummins. I have an appt. Friday. I pisses me off to have to take eq. to the dealer. Please advise. Ron

Hello, Ron. My name is Hank.

If you are familiar with car engines, there is no reason you can not work on this yourself. Just think on a little smaller scale. The basics are the same - you must have fuel (you smell propane), compression and a spark delivered at the right time for the engine to run.


Let's start with the basics. You say the plug is good, but were you just looking at it or did you actually check for spark? First, disconnect the electrical line at the fuel shutoff solenoid so we don't have LP flowing while we are testing. If you have a vapor withdrawl system, the solenoid is located beside the regulator. If you have a liquid withdrawl system, the solenoid is located a the back, right side corner of the genset. One at a time, remove the plugs. reinstall the plug wire. Holding the wire or boot with insulated tools so you don't get shocked, hold the base of the plug against ground. The heads work good. Crank the set and see if you get a good spark to both cylinders.

While you have the plugs out, do a compression test. If you do not have a compression tester, do a basic check by simply putting your finger in the spark plug hole and crank the set. It should have enough compression to push your finger out of the hole.

If you get no spark, test for 12V at the positive terminal of the coil while cranking.

If you are getting spark, reinstall the plugs and wires and remove the air filter. Spray a shot of fuel directly into the carb while cranking to see if you can get the engine to hit. A bit of propane from a torch (not lit) or carb cleaner works.


Are you getting fire to the plugs? 12V to the coil?

Good compression?

Does it fire when adding fuel?

Customer: replied 6 years ago.


Thank you for your attention to this matter. Knowing that I can approach the problem as a car engine I will do your tests this afternoon and get back with you with any further questions.


I appriciate your detailed email and will definitely accept you anwer upon completion. I will get back with you this afternoon with my results.



No problem.

Remember, you do not have to accept if you are not completely satisfied. I am not perfect, but I strive to do my best. If when we get your set going and you believe I have earned it, then you accept.

Customer: replied 6 years ago.
Hey Hank, I immediately checked the 12v at the coil, and zero volts. I checked the three pigtails at the genset and have strong voltage, as well as at the starter wires. Grounds look clean and good. This gen has only 180 hours on it. I checked the 10 amp barrel fuse on the gen set by the strart button and is fine. Also checked the 12v distribution panels with fuses inside panel, and the main electric bay. There is NO fuses or breakers other than the one by the start button on the gen set. Oh, both 30 amp breakers on the gen set flipped correctly too. So no fire to the coil. Any ideas? Ron
Customer: replied 6 years ago.
Help please, See my last reply at lunch time. thanks, Ron


No 12V at the coil while cranking is one of 2 things.

Either a bad control board or a broken wire between the control board and the coil.


Remove the control panel. The control board is attached to the inside of the control panel. There is a 12-pin connector on the panel, with all wires numbered. All of the wires will begin with J1- and then the nubmers 1-12.

Set your meter to ohms and conenct the black lead to a good ground. Leave the plug conencted to the board for all of the following tests.

1. Check for continuity between wire J1-1 to ground. This is the ground wire and should show continuity.

2. Set your meter for VDC and check for voltage at pin J1-7. It is the control power for the board and should show 12V.

3. Check for voltage at pin J1-12 while cranking. This is the output to the coil. It should show 12V while cranking.


If there is no continuity at pin J1-1, either that wire is broken or disconnected from the lower terminal block located all the way to the back of the control box.

If there is no power at pin J1-7, either that wire is broken or is disconnected from the 'I' terminal of the start solenoid.

If the first 2 are good but there is no power to pin J1-12 while cranking, the board is bad.

If there is power at J1-12 while cranking, then that wire is broken between the plug and the coil.


Also, that 10A fuse is supposed to be a 5A fuse.


Please let me know what you find.


If we discover the board is bad, you will have 3 choices.

1. Get a new one from Cummins.

2. Get a new aftermarket one from another company that makes a good quality product for much less money.

3. Send your board in to that company to have it rebuilt for even less. They offer rebuilding services for about $75 for most Onan boards.

Hank F., RV tech - emphasis on gensets
Category: RV
Satisfied Customers: 14412
Experience: RV tech since the beginning of the millenium.
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