Help with Onan 5000 starts won’t stay running.

Some of the older KY series and some others have a quirky setup, the output voltage is directly related to the input voltage, 12 volts in, 120 volts out. The excess gets clipped, but it has no ability to boost low voltage so if it’s 9 volts in, it would be only 90 volts out.

As a safety measure if the output voltage is too low it shuts the engine down as soon as you release the start button so you don’t burn stuff up.

The easy test is to continue hold the start button down after it starts and see if it keeps running. The starter button bypasses all the safety’s while it’s engaged.

If that works check the engine battery and / or try starting it with the coach engine running, the alternator will fool the genset into thinking the battery is fully charged.

The generator is a 97 so there is no light to check for a code on it.
We tried connecting it directly to a gas jug with new gas and seafoam in it.

When the generator stops normally the indicator light blinks a pattern
Like 3-3-2 3-3-2 3-3-2 (the pattern is usually longer) Write it down and post it

Then we have a clue
Some things that can cause that
Dirty slip rings
Bad oil pressure sensor
Other bad sensors
Bad control board (The parts that read the sensors)
and so on.

But with the code we get a clue.

Dirt slip rings often report as "Cranking speed too slow or low battery" by the way.

Is the gas old?

What code is it showing?