1990 ONAN 4K Only cranks once- HELP !!

[Davemandu]

I don't know what to do!! My ONAN 4000 is from 1990. I bought the Class C RV off the back of a lot as-is. It is a great starter unit for me to join the camping world with my family. Everything on our 1988 Mallard Sprinter works great EXCEPT for the generator. When I press the start button it only cranks over once, maybe twice but then nothing. I checked the battery cable that goes to the battery under the hood, changed the battery with a brand new 850CCA battery and still does the same. I cleaned all the battery connections and still the same. Nothing I do seems to change this. Seeing as I beat the dealer up on the price (he wanted $9k and I gave him $4500, it was an "as-is" deal so I can't go back to him). If it'll help I can post a picture of the unit, but hopefully someone can help me find the answer, thanks everybody!

[94-Newmar]

If it literally won't turn over but one or two revolutions you could have two problems:

1) Battery cables are corroded or bad either at the connectors or somewhere inline.

2) Something may be obstructing the crankshaft of the engine. Perhaps a broken connecting rod or some other internal component.

Had this generator ever worked since you purchased the unit?

[Davemandu]

no, it has always done this since we picked the unit up a month ago. I have checked the battery cable that goes to the solenoid, but I don't know where the ground cable is. How do I check the voltage at the solenoid? Maybe I should check that to make sure there's enough voltage getting to it.

[94-Newmar]

The chassis or engine block of the generator should have the ground wire attached to the battery(ies). Use your voltmeter to check between either large wire on the solenoid back to the chassis of or the engine block of the generator. If you're unsure then snap a pic of your solenoid, post it here, and I can point out where to probe with your voltmeter.

HOWEVER it is possible to see a good 12 volts there but if the cables or connectors are corroded internally or partially broken you won't get the amperage you need to turn the unit over, yet you can still see a good 12v there.

[Davemandu]

ok, I'll do that now and see what I can come up with, thanks!

[94-Newmar]

If you have good clear access to the start solenoid might I suggest something...

Using a good jumper cable set and another known good battery you could hook up temporarily to see if either your current battery or your cables are the problem. Ground can be found anywhere on the generator chassis or engine block and positive on the same side of the solenoid that your current mounted battery is connected to.

If I remember correctly, the Onan 4000 series gensets from that era should have a manual start button on the control panel mounted right there.

On a side note, it is also entirely possible that your starter motor is bad - thus being too weak to turn the unit over.

[Davemandu]

okay, here's what I have so far. I put the volt meter on the positive post of the solenoid and it reads a good 12 volts. Then I had my wife press the start button of the genny and it cranked twice and dropped down to 3 volts when she let go of the button it went back up to 12 volts. I have to admit that I am pretty electronically illiterate so I don't know what that means.

[94-Newmar]

That means you have a bad cable OR bad connector on either the battery end or the generator end... generally you'll see a 1-2 volt drop, but not that much. See my previous post, grab a good set of jumper cables and see what you come up with.

[Davemandu]

will do. Thanks again and I'll let you know how I make out.