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RonnieG

Onan BGM Generator Won't Start

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My 2000 Southwind is equipped with a Onan BGM 5500 gas generator. It ran fine then just suddenly stopped running. So I naturally went through the basics, - Ignition induction, fuel. If I put starting fluid into the intake, it started but failed to stay running, so I went to the electric fuel pump. I replaced it because according to the manual it's supposed to develop 3.5 psi and it didn't seem to do that. New pump in, it still wouldn't start! At the suggestion of a friend, I hot wired the pump and primed it. The BGM started right up and ran fine (pumps a little noisy, it clatters when running) then I shut it down and went the next day to start it again and it would not start. I can't find any reference in the service manual as to how the BGM primes the fuel system, so I'm thinking of wiring in a primer switch to the pump to prime it prior to each start. I have seen later models of the same generator which have a prime switch incorporated into the start switch. I'm looking for imput on this idea or if someone knows how the prime system works in this model and I need to do something else, please give me the information

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Ronnie,

This may be redundant but how is your Oil level? Is your fuel tank below 1/4 empty? Low oil level and pressure can cause the engine to not start and low fuel, below 1/4, will not let the engine start and run. This is son you wont run the tank empty when running the Gen Set.

Just a few thoughts. Thoughts are like giving Chicken soup for a dead person,"I may not help but it can't hurt".

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Other than low fuel level, another common fuel-related issue on 10+ year old coaches is that the fuel line to the generator has started to break down. A small crack between tank and generator will allow air into the line.

An easy test since you are familiar with working on the fuel pump is to run a gas line from a gas can to the pump-- see if that will keep it running.

Brett

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I should have stated earlier that I'm aware of the oil and fuel level cutoff's that are built in safeties. The oil is full-full and this has occurred with a full tank, and currently it's a one-half tank. I think there is a priming mechanism in the starting, but I just can't seem to find it mentioned in the service manual or see it in the schematics. When I stared it by "Hot" wiring the pump to prime it, I disconnected the circuit and hit the starter. The pump began to operate several seconds after the engine began running (I could tell this by the clatter this pump makes when energized) as if there is a pressure switch or electronic mechanism that turns the pump on. In regards to fuel lines, I replaced ALL the rubber fuel lines with new and have visually inspected the metal fuel line to it's entry into the coaches fuel tank (that's not fun for an old man on a creeper). Nothing seemed amiss during the inspection, but it might be worth another look. I keep coming back to the pump, which doesn't seem to get voltage until "after" starting when I would think I should hear it working during the starting process. Any thought's. By the way, when it run's it runs perfect and it will run both of my roof A/C's without a wimper. The individual I bought it from must have taken good care, because so far everything work's very well and appears to be maintained well and I intend to keep it that way.

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Ronnie, Again, you may have checked but how about the fuel filter. Also call Onan with your model number and serial number and ask about a priming process.

Herman

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Herman

New fuel filter, new fuel lines. Your right though, I should call Onan and ask them how it works!! I guess I'm just used too a more thorough sevice manual with better detail of system operation. This manual just doesn't seem to go into detail. I'll update after I talk to Onan next week.

Ron

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I guess I'm just used too a more thorough sevice manual with better detail of system operation. This manual just doesn't seem to go into detail.

Ron

Talk about wishful thinking. :D:lol::D:lol:

Herman

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I think the only way you will truly find out how the generator works and how to trouble shoot it is to buy the "real" service manual. The ones we get are just "owner's" manuals and really don't help much...

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This is the "Real" service manual, purchased from Cummingsonan and it's still not as detailed as it should be.

Ron

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FWIW, I have been through the bad fuel line routine..... replaced it twice (I should have gone metal). But I have also suffered from a self-inflicted wound on 2 occasions ---------- a varnished carb. I've had to replace the carb twice. The second time came as a total shock..... but that was the problem correctly diagnosed when I got back home to my generator repair place. I took it to 2 RV dealerships on the road. Replaced fuel pump, circuit board, fuel filter, etc. Still wouldn't run for any length of time. I now carry a spare carb with me.

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A varnished carburetor is a symptom of not exercising the generator enough. Said another way, the good gasoline evaporates, leaving a residue.

Couple of choices:

1. Exercise the generator as it should be-- once a month for a minimum of 40 minutes at 50% load.

2. Install a ball valve in the fuel line and run the generator out of fuel (best if all electrical loads are off when you do this) so no fuel sits in the carb.

3. Use Stabil or other fuel stabilizer when storing the coach.

4. 1 and 3.

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Brett:

As I stated, the carb issue was self-inflicted........... not enough of 1 and 3. LOL But, Ronnie G didn't mention the carb or eliminating that as a possibility, so I thought I would share my story.

When my carb had to be replaced the second time it came as a real shock as I had run the generator from Plano, TX to Cloquet, MN (over 900 miles) pulling 2 air conditioners on a hot June day. When I shut it down for the night, it would not start in the morning. After running for such an extended period of time I was sure it wasn't a varnished carb. As mentioned, we replaced many things other than the carb. Never did get it to run more than a few minutes until we got back to Texas. It was one hot return trip from Canada. Parker Power Systems in Carrollton, TX (who I have been using for over 25 years) replaced the carb and it has run great ever since. And yes, with lesson learned I now use a little more of 1 & 3!!

I still can't believe that was the problem........... but it was.

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Planocat,

Indeed, varnishing isn't the only thing that can render a carburetor DOA. It is, however, the most common.

Brett

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Once again, "different stroke for different folks" the onan service manual doesn't address "carb priming" in the fuel section. The Electronics section says that upon pushing the start button, you energize a relay which turns the fuel pump on for starting. This is apparently the earlier method of priming. A friend owns a little bit later model, and it has a direct priming switch. I'll check to see if the rely is working first, then the circuit board. My current thought is to put my own priming switch in a do away with the relay. We'll see.

To Planocat, I "hot wired" the electric fuel pump to prime the carburetor and the Generator started fine and ran well and produced all the energy I need for several hours. So I can only assume that the carb. is fine the way it sits. As I said earlier, I replaced all the fuel lines because they were old and I was going underneath anyway! Thanks for your input.

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My manual says to crank for 10 seconds. Looking at a watch, that is a long time. Wait for a 5 seconds and crank again. Normally the first 10 seconds is priming. Next five is cooling starter, then next crank starts.

You said yours is running great when you get it started. Be sure to check the winter/summer air setting if yours has one, air filter condition, and linkage for choke/governor. Hard starting may also be related to spark plug wear.

Sometimes it is the simple things. Had an issue with my Onan 7500 with loping. Finally discovered that the two bolts that hold the carburetor had worked loose and was allowing air in. Boy was I happy it was something easy. Just took awhile to trace it down.

Let us know what the final solution is.

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