Arghh!! Generator shutting off

[92landyacht]

Just got back from a 4th of July trip and everything went well except for the generator. Some times it runs for a couple hours and sometimes it will only run for 10 minutes. Every time it sputters and quits. Checked the oil level and that's OK. Sounds like it's running out of fuel. The Genset is a Onan NHM Marquis 7KW unit. Guess I've got some troubleshooting to do.

[AdamB]

Fuel filter or low fuel level? Mine is surely different (Powertech/Kubota 7000W diesel running off the 90 gal main fuel tank), but it won't work without at least 1/4 tank of fuel in the tank. I also went through about 4 fuel filters when I got my motorhome 3 years ago to clear all the junk out of the lines. It kept stalling on our first trip until I went through at least 3 fuel filters. I also changed the air filter, oil & oil filter later. It runs great now and we do a lot of camping in county, state & national parks w/o hookups and we rely on our genset a lot.


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[J. Morgan]

Maybe getting hot and/or vapor lock?

Gas ain't what it was, with fuel injection becoming the rule, gasoline boiling temperature has dropped, so I have read anyway.

(Since gas constantly recirculates with fuel injection, it is not sitting in one place to get hot so the boiling point is not as critical as it used to be)


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[92landyacht]

Originally Posted by AdamB

Fuel filter or low fuel level? Mine is surely different (Powertech/Kubota 7000W diesel running off the 90 gal main fuel tank), but it won't work without at least 1/4 tank of fuel in the tank. I also went through about 4 fuel filters when I got my motorhome 3 years ago to clear all the junk out of the lines. It kept stalling on our first trip until I went through at least 3 fuel filters. I also changed the air filter, oil & oil filter later. It runs great now and we do a lot of camping in county, state & national parks w/o hookups and we rely on our genset a lot.


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Tank is over 3/4 full so I don't think that it's the problem. I was able to pump a quart of fuel out into a clear container and found no debris in the fuel. Fuel filter is not obstructed.

Today I added a fuel gauge after the fuel filter. I ran it until it quit (about 1.5 hours). I tried to restart it but it would not build any fuel pressure. I disconnected the fuel line and could see only a dribble of fuel when cranking. I sucked on the fuel line while cranking and found no obstruction to fuel flow. Conclusion at this point is that the fuel pump is going out. I ordered a Carter P4070 fuel pump. The OEM pump sells for over $230 and is made by Carter. Same shape and the same output pressure (4-6psi). I'll update once the pump arrives. Not looking forward to installing it though.

[bkahler]

Another possibility is the suction line (from fuel pump to tank) has cracks in it. Your Land Yacht will cause all sorts of running and starting problems for the generator.

Worth checking into.

Brad

[92landyacht]

Originally Posted by bkahler

Another possibility is the suction line (from fuel pump to tank) has cracks in it. Your Land Yacht will cause all sorts of running and starting problems for the generator.

Worth checking into.

Brad

Good point Brad. I'm actually hoping that it's the pump since tracking down a leak in the fuel line could become even more problematic.

I'm thinking the fuel pump will do it since the pump couldn't pull any fuel but I was easily able to pull fuel by simply sucking on the fuel line. It seemed like the pump had no prime capability. The fuel was clearly right there at the pump, since it took nothing to get fuel to flow with a light vacuum on the line, but the pump still couldn't push any volume or build pressure. Almost like the pump was stalled. I'll let you know since I just got notice that the pump arrived at the house.

Probably going to bypass the current pump and let the new pump pull fuel from the original line to test it. That will tell me if the original pump is bad before I go ahead and attempt to yank the old one out.

[bel73]

Also check the vent in the cap. If it is clogged up it will cause a vacuum in the tank and not let the fuel flow. This happened to me once on my riding mower. After I changed the filter, plug and cleaned the carb twice I finally figured it out.

Try running it with the cap loose to see if it still dies.

[92landyacht]

I would think that the engine would have issues then as well. The 454 engine has no issues with running down the road for hours. It draws from the same tank as the genset and pull a ton more fuel/hour.

Replacement fuel pump arrived today. Carter P4070. Looks identical to the OEM Onan pump and has the same pressure rating at 4-6psi. Once I remove the original pump I'll be able to compare item to item. Price difference alone is worth the experimentation. $230 v/s $64 delivered.

[Farmer Dan]

This is a simple suggestion that may or may not work. Get some Sea Foam gas treatment and put in the gas tank. You may have a jet or small passage that is partially gummed up on the genny carb. This additive works for us on small engines on the farm whether its seed tenders, lawn mowers or ATVs with Honda power, Briggs & Stratton or Yamaha power. I usually end up with it mixed stronger than recommended, but have no problems. I think its a petroleum product anyhow. It'd be an easy try.
Dan

[hissilver]

One other source for your problem may be a fleck of carbon has attached itself to the spark plug and is not allowing the spark to fire and ignite the pressurized fuel...just a thought

[92landyacht]

Guys, thanks for the input. I've confirmed that, when the problem is occurring, no gas comes out the fuel line when the gen is cranking. After sitting for a while it will pump gas but not for more then a couple hours. Sometimes for a little as 10 minutes. If I feed gas to the carb it starts and runs fine. I figure I'll be able to try to bypass the pump on Weds if weather permits. That will tell me if it's a pump or feed line issue. It's not a gummed up carb problem for sure. Whenever I put gas in the MH I add the appropriate amount of STA-BIL fuel stabilizer.

[bkahler]

Originally Posted by 92landyacht

I would think that the engine would have issues then as well. The 454 engine has no issues with running down the road for hours. It draws from the same tank as the genset and pull a ton more fuel/hour.

One thing to keep in mind, the genset has a different tap into the fuel tank than the 454 engine tap. The genset tap doesn't stick down into the tank as far which means you can't inadvertently suck the tank dry while camping in the middle of nowhere

Replacement fuel pump arrived today. Carter P4070. Looks identical to the OEM Onan pump and has the same pressure rating at 4-6psi. Once I remove the original pump I'll be able to compare item to item. Price difference alone is worth the experimentation. $230 v/s $64 delivered.

That's good to know. Where did you order the pump from?

I've attached a couple of pictures of how I did the suction line plumbing on the Kohler in the 310 I used to own.



I bought two 1/4" plastic shutoff valves like those used on lawn mowers, etc and also a 1/4" plastic Tee. One shutoff valve goes in the suction line to the coach fuel tank. The other shutoff valve is on the other side of the Tee and I attached about a 5' or 6' long piece of hose to the other Tee that I use to stick into a gas can for testing purposes or if I just want to run the genset for a while without pulling fuel from the main tank.

You have to keep one of the valves closed all the time or the pump won't be able to generate any suction. This arrangement has come in handy several times when I had to troubleshoot problems with the starting/running of the Kohler genset.

Simple and cheap to do and it seemed like a worth while modification.

Brad

[bkahler]

Originally Posted by 92landyacht

Whenever I put gas in the MH I add the appropriate amount of STA-BIL fuel stabilizer.

That's something I should be doing as well. Just need to remember to do it

[92landyacht]

Ya, I keep a quart of STA-BIL in one of the lower compartments near the fuel inlet. I figure about how much I'm going to need to fill or put in and dump one Oz per 5 gallons in before I fill. Haven't had a gas related problem for years. Even after sitting for months.

[92landyacht]

Replaced the fuel pump today.... Tried to get at it with the generator installed but decided that wasn't going to work out. Ended up dropping the generator using a floor jack and board to distribute the weight. This gave me a lot more room to work with.

Replaced the fuel pump with the Carter P4070 which did turn out to be an exact replacement. Everything bolted right up with no modifications except the power lines. The stock unit used nuts and bolts to attach ring crimp fittings while the new one had press on connections with pigtails and spring clamps. Cut off the rings and used butt splices to attach the pigtails with no problem.

Static fuel pressure is right at 5 psi. While running under full load the fuel pressure varies from 5 psi to around 3 psi. Ran the generator for about an hour with out a hiccup. The old fuel pump pressure would vary all over the place from 8psi to almost 0 back and fourth rapidly, so I think I'm in much better shape.

At least I know I can use a fuel pump that's not $280+. The pump I purchased was from an ebay seller. It was new and in the original box with all parts sealed in the original bag. Paperwork and warranty card included. Even if you don't find a deal like that they only cost around $85 from many suppliers. The original Onan pump had no markings on it at all except what looked like a serial number. Not even an Onan part number was attached. I suppose it possible that the Onan label had long since fallen off.

Well... Onto the next project. New AC Delco front rotors purchased from Rock Auto.

[92landyacht]

Just an update: After installation of the new fuel pump I'm happy to say that the pump is working perfect and I haven't had a single issue with the generator. Spent 6 days boondocking at the Petit Lemans road race event. Ran generator for between 1 hour to over 10 without a hiccup. The Carter P4070 pump worked flawlessly. Great alternative to the stock Onan pump. Reads a solid 5psi with the generator running.