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Home » Public Forums » GMCnet » [GMCnet] I give up. (Onan)
[GMCnet] I give up. (Onan) [message #190227 is a reply to message #190105] Tue, 13 November 2012 22:05 Go to previous messageGo to previous message
Robin Hood is currently offline  Robin Hood   United States
Messages: 1078
Registered: April 2011
Karma:
Senior Member
Oh Emerald One, tell me your seeeeecrettttsssss....

I have messed about further with my Onan. Observations:

To make life easy on myself, I went ahead and primed the carb by jumping 9
to 5, then disconnected the jumpers.
Pressing the start button caused a "run" condition, but ONLY when the start
button was kept pressed/engaged..
Hooking the jumper back up to 9 and 5 and pressing the start button started
the Onan, which continued to run even if I let off the start button.
Disconnecting the 9 to 5 jumper wire IMMEDIATELY killed the engine.

What this tells me:

1. I have sufficient fuel, air, spark, and compression for the engine to
run once its other problems, whatever they are, get worked out.

2. The engine isn't immediately dying due to lack of fuel upon removal of
the jumpers. There should be plenty left in the fuel bowl of the carb to
keep running. That is to say, the problem isn't the fuel pump. Only a
sudden halt of spark would kill it that quick, I think.

Assuming for the sake of argument that the board is good, this leaves me
with the following possibilities: That there is low oil pressure (bad),
that there is good oil pressure but the sensor is throwing a false sensor
reading (also bad, but may be easier to fix), or that the board isn't
seeing what it wants from the Voltage Regulator.

Following Duane Simmons guide, I removed from its terminal wire #12
associated with the oil pressure switch, and tried starting the engine
unjumpered. It still wouldn't run. I hooked up my multimeter to wire #12
with the engine not running. I grounded the COM (black) probe of the meter
to lots of places including the negative terminal of the battery. It should
have read 0 ish ohms, but it was an open circuit. Thing is, an open is the
"hey I've got oil pressure" condition. I may as well leave wire 12 off and
run without oil pressure monitoring. That's a bad idea... But while it
seems my oil pressure sensor is failing, I think it's failed in a state
that permits operation. So... I don't think that's my problem, although I'm
not super confident. I could just suck at using a meter. I'm out of
practice and out of my experience level.

That leaves the AC is-engine-running sensor as a likely culprit. There are
3 terminated wires attaching to blades on the voltage regulator. One is
labeled B+ (I assume it's battery positive) and the other two are labeled
AC. I assume these are the two AC legs. Mr Simmons advice here is a bit
ambiguous... He advised disconnecting the voltage regulator... But I'm
unclear as to what to do with the wires. Am I supposed to connect the two
AC wires I just removed from the regulator TOGETHER as in electrically? How
is that safe if they're 2 different AC legs? And in what way does doing any
of this make the control board happy?

I've read Simmons guide and studied the schematics and watched the DVD, but
if anyone has help or advice all ears.

Robin


--
Robin Hood
Jackson, MS
2003 Buick Lesabre
1968 Pontiac Catalina
1978 GMC Royale motorhome
1977 GMC Palm Beach motorhome


--
Robin Hood
Jackson, MS
2003 Buick Lesabre
1968 Pontiac Catalina
1978 GMC Royale motorhome
1977 GMC Palm Beach motorhome
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