1977 460+4 Automatic -- Motorhome Chasis:

Had a problem with my Onan GenSet - was blowing fuse shortly after start up. After digging into the Onan manual I discovered discharges from engines alternator could be a cause...

Then I realized the problem was occurring while the coach's engine was running (which I did to get the house battery charge going).

The other day while running the engine, I discovered that the ammeter was bouncing around alot - so I monitored it for like 2-3 minutes...

The charge indicated about +5 pretty regularly yet would travel rapidly back and forth varying from +30 to 0 on occasion and in some instances from +60 to -10 or so...

UPDATE: Ohyeah,. Every once in a while while idling (usually on/near start up) and sometimes while driving the engine on this beast just shuts down. I am thinking that it could have been the alternator?

I also read another post and reply in this forum: When this happens it fires up after cranking and pumping a bit. When cold I also have to pump it up like. It would backfire when it went to cut out.

It had an after market inline fuel filter installed by prior owner (for additional protection, replaced that and it got much better,. Now when it shuts down,. it shuts down like turning like as if you turned the key off - no backfiring any more.

Perhaps I had a multi tiered problem and solved only one part of it?

I am wondering if the alternator discharge was/is causing the engine to cut out or not (yet I don't recall the ammeter ever bouncing like it does now, maybe a little, and attributed it to age and perhaps like a typical vibration - although it run pretty smooth.

The other day when I noticed the ammeter, I also noticed a slight noise coming from the area near the alternator,. thought it could either be that or the water pump. was not the typical noise water pumps make,. was more like an intermittant thing - leading me to think it may be the alternator is simply shot? will update/perhaps cut some out on this post soon.

So,. Fuel pump? Alternator? Ground? Faulty screwflatchet - bent wingdinger?? What? Seriously would like to know how I can test rather than replace items blindly.

Will take trip to parts store and test the starter, alternator and both house and the engine batteries.. and update form there..

Dig this forum -- Thanks so much everyone!

 

The alternator would not cause it to shut down. Did these problems start after the generater hook up ?
I would have the alt. checked first. Then try a known good regulater.

 

Sure it would! If the diode's are bad in the alternator the only voltage that the vehicle is getting is what is built up in the battery, eventually that battery is going to go dead. With no juice from the battery you have nothing to make spark with.

I would check the alternator and it does not hurt to add more ground strap's.

 

He said he cranked it for a while until it started once it died. Oviously the battery wasn't

 

I am lost on this one. What kind of system is this? How many batteries, and what does each battery do? Is there a battery isolater in the system? The onan generator can charge the battery that starts the engine and another battery that runs the appliances in the camper at the same time? Can the engine alternator charge both batteries too? Sounds rather complex to me.

 

Sorry, I guess I miss understood your post. I had thought you meant that a bad alternator would not stop a motor from running, please accept my humble appology

 

Hi Dave,. thanks for the hit.. Let me see if I can clarify..

The system is dual "most" all the way.

As you know, the coach's engine provides power to the drive train and its electrical just like any other vehicle would. The battery is typical - designed for the high-energy burst of DC power needed to turn an engine over for occasional start up of the drive train engine.

Note: The Alternator from the drive train engine can recharge the house (onan genset) battery.

The Onan generator also has its own battery and it's complete system. It has a deep cycle battery with thicker plates for a longer, regular ongoing like draw of DC converted to (Alternating Current) juice/power, which is used for appliances, etc. The battery is designed to start the onan genset.

To the best of my knowledge, the onan ggenset charges its own battery only and not the engine battery - again to the best of my knowledge.

Both batteries are synchronized such that the drive train engine alternator can charge both batteries (while the onan generator is off or on).

It is also conceivable to run one (or both) engines simultaneously and have charging happening with both batteries as they require or as necessary.

In fact, I do have three starter solenoids,. one on each side of the engine compartment with each of the batteries and one on the onan generator inside the genset itself.

Hope that makes sense?

Please also recheck my newly updated post.. Going to work on that now. THANK YOU for any feedback here!

 

thanks guys for everything... here is an UPDATE:

Had the alternator tested -- It is good. The test revealed that the engine battery is supposidly beat -- according to Advance Auto Parts testing machine. Not sure I believe that as that battery can take some cranking and still holds up quite well... (have not had to jump it). Will try another auto parts store to be sure of the testing machine.

Back to start again? Oh MY! -- Let me see if I can shorten this a bit and omit the onan fuse blowing issue as it is more or less its own entity all be it is connected to the whole system (see reply to (Franklin2) in here)

Regrouping here: The drive train engine shuts down on occasion - Just like someone turned the key off. Typically it happens more often at idle shortly after start up - sometimes tries to cut out at higher rpms although not as frequent.. I can count on it cutting out 2-3 times on start up. After it cuts out, I have to crank and crank and crank.. (usually it fires when I let off the key from cranking).

It used to back fire and cut out while driving - until after I replaced an inline fuel filter and that ended that.

--- As for the Ammeter guage bouncing around as mentioned in the original post - when they hooked up the tester at advance auto parts to it - the after market ammeter guage did not seem to bounce as much and stabilized during that time - I have not played with any of it since the test. I am thinking the ammeter guage itself may be weak - if the testing machine was in fact operating correctly.

Typically to start her up, I have to do a lot of pumping, crank it,. stop cranking, pump some more, and then crank again. It fires up more often times than not when I let off the key from cranking... Lately it seems to be takign more to start when cold than before.

It still fires and runs real well for the most part, I'd just really like to isolate it and get past this.

The timing seems to be ok, although I have not put a timing light on it yet and engine runs smooth, stay in 180 temp and all that too.

-- I am thinking it is a coil issue. Not too sure how to test this coil as it is aftermarket spark system - high voltage - and electricity and I do not get along that well to begin with! - Will contact the mfgr and see what they say. For gigles I will re-hook up the old coil and see what happens as I left it mounted for emergency if needed.

--- Also: I added an extra ground cable on the house battery to the Air Conditioning pump - otherwise would need several more feet to get to the frame. Did not add additional ground to the engine battery yet - and will add ground to the engine battery also.

--- The Onan generator is original to the coach, was working fine until its fuse started blowing - Onan's are known for being cluegy and are a whole other ball game in their own right - (more of a real pita than anything, yet very nice to have when working correctly). If the alternator is not discharging then I think that problem may be isolated to the onan.

Will continue to dig.... any and all responses are welcome! Thank you all!

 

All the pumping on start up, and the occasional stall right after from a cold start, sounds to me like the choke is not working on the carb.

The engine needs a very rich mixture to start and run when it's cold. The choke blocks the air going into the carb to make it rich enough to start and run. What your are doing by pumping the pedal is squirting raw fuel into the engine to make it rich enough to run. With the engine cold, take the aircleaner off, and you should see the choke plate on top of the carb. It may be open. Go into the cab and push the gas pedal all the way to the floor and let up. Go back under the hood, and the choke should be closed. You can push on it a little to try to open it, and it should have some pressure on it keeping it closed.