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Re: [GMCnet] Onan - Vapor Lock? [message #179626 is a reply to message #179617] Thu, 09 August 2012 01:07 Go to previous messageGo to previous message
ljdavick is currently offline  ljdavick   United States
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma:
Senior Member
Rob,

Thinking about your spark issue - when cranking is it possible that the voltage is low enough that the Pertronix won’t Pertron? (I’m guessing that you have the Pertronix electronic ignition in place.) Maybe it’s a matter of a loose or corroded battery connection.

Does that make any sense?

Also from the Onan manual on page 23 -
B - ENGINE CRANKS BUT DOES NOT START -
1B Is F1 fuse on control board OK?
3B While engine cranks, check K1-I start solenoid voltage. Is 12 vots present between terminals 10 and 1? If no Replace K1 start solenoid.
4B Jumper terminals 9 to 11. Does engine start when start switch is pushed? If yes - K2 contacts are defective. Replace printed circuit board. If no - Fuel solenoid K4 must be open during starting and running...
Then it goes on to diagnose the fuel pump and then the choke. If none of these then it states
13B - The fault is in the ignition system. Check points, plugs, wires and coil. Refer to IGNITION section.

On page 28 it states STARTING;
Push start switch S3. Battery current flows thru K1 solenoid, K2 contacts and start switch S3 to battery negative (GND). K1 solenoid closes contacts, feeding current to starter motor and to choke E1 plus K3 relay. K3 relay contacts close the circuit to the ignition coil T1 and fuel pump E2 plus fuel solenoid K4. The engine cranks and the fuel pump, fuel solenoid, and ignition operate to start the engine.

Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, CA

On Aug 8, 2012, at 9:13 PM, Rob Mueller wrote:

> G'day,
>
> Well it's Wednesday and I decided to play with the Onan some more. After I sent the message below Marc and I discovered something
> else. The Onan wouldn't fire when cranked but the INSTANT the start switch was released it would fire. We pulled the plugs and sure
> enough with the start switch depressed no spark, the INSTANT the switch was released you'd see a spark.
>
> I have a couple of spare boards so I figger'd I stick on in and see what happened. NOTHING! SAME PROBLEM. Tomorrow I'll stick in the
> second spare and see if that works.
>
> I did a few other minor jobs on the GMC which needed doing which pleased Helen and that's important! ;-)
>
> Regards,
> Rob M.

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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy

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