Onan Fuel Pump

swebster · 08-02-2003, 02:07 PM

OK...so far the 345 has been better than expected. I'm mostly working on minor issues but still have one large issues to tackle - the generator.

My first few tests showed no spark at the plug. So I replaced the points, plugs, (no one could find the coil for me, not the dealer or my NAPA guy. Cummins was closed today so I couldn't check there.) Once everything was replaced and gapped correctly I had spark. Many thanks to all of you who told me to replace these.

Now for the fuel part: I drained about a gallon of "stale" fuel from line that goes into the pump, opened the pump and cleaned out that fuel, carb cleaner down the carb, etc. But she's still not firing up. On to the fuel system...here is what I found out so far:

Based on the following procedure I can get it to fire and run for about 30 seconds. Then it dies:

Connect the fuel pump to a 12V power source other than its connector for about 60 seconds with the generator off.

Reconnect the fuel pump power to its connector.

Hit start....she fires and runs for 30 seconds then dies.

She will turn but not fire again unless I move the power source on the pump. So I think I have a power to pump issue. The strange part is if I crank her with a voltmeter on the connector I get a steady 12V on the connector.

I'm looking for any and all suggestions. I'm headed to Pep Boys to see if they have a cheap electric pump I can throw in there for now until I can get to Cummins.

swebster · 08-02-2003, 05:25 PM

I've been working on this now for almost nine hours

!

In any case, I can now get it to start without bypassing the 12V into the pump, but the gen revs up and down a little then dies. Won't restart unless I let it sit for a while.

I went to NAPA just for fun and the only thing they had was a booster pump that moves 35 gals per hour. I passed since the Onan manual said the generator should use only 1.5 gals per hour. Seemed like a mismatch to me.

Going to pull the pump and see what I can see next....

PeterH-79MH · 08-02-2003, 05:58 PM

The most common problem I found on these older Onans is the carburetor. Fuel could have been in there for month at a time and they are all gummed up with sticky floats and clogged passages. I had success before with using small amounts of carb cleaner through the air inlet to get them going and keep them running.

swebster · 08-02-2003, 06:03 PM

Peter,
I've tried that as well. I didn't want to get into complete dismantling of the carb but I'm beginning to see more and more signs of life than lead me to believe it could just be gunk in the carb. Now it starts on its own, revs then dies. We're getting closer!

I'll try some more cleaner in there tonight and see what happens.

PeterH-79MH · 08-02-2003, 06:48 PM

Steven,
I trust you are doing all this with the power to the coach disconnected from the genny. You don't want to send all this erratic voltage to whatever is connected inside (i.e. univolt, microwave...)
But something tells me you thought of this already.

FrankR · 08-02-2003, 06:54 PM

Napa Auto parts has some magic elixer that will clean a fuel system that has foul fuel. Most guys get the magic and mix up a gallon of fuel in a container not associated with RV or parent fuel tank. The ngine will stumble for a while but will clean up the carb and run properly. The engie can be made to continue to run with a few squirts of either. This Napa magic was developed for small engine of all kinds, mostly outboard engines.To prevent to future occurance of bad fuel in carb is to remove feul line from pump. Start engie and allow engine to run dry of any fuel. Old small engines has been doing this forever.

Pic of my new treasure

swebster · 08-02-2003, 07:22 PM

Fred,
I have disconnected everything from everything. After even more carb cleaner it will run steady for a few minutes and then die. My friend (who came over to stand behind me an offer advice - but to his credit owns a boat with an even older Onan on it) suggested that mabye there is a primary and secondary needle on the carb and it bails when the seconday kicks in. I have no experience with Onan carbs so its a guess.

The idea of rebuilding the carb does not appeal to me if I can run some cleaner through it and get it working. I'll certainly look for a solution in a bottle before breaking that first gasket.

**john hd** · 08-02-2003, 07:38 PM

steve

sounds like you are on the right track with the fuel problem.

as for the coil, do both spark plug wires come out of each end? and is there a wire teminal for the feed wires on each end? about the size of a small soup can?

if yes, go to a harley dealer and ask to see what they have for coils.

i guessing that onan uses a wasted spark system like harleys.

sould be an exact match.

we have pulling equipment at the power company that uses wisconsin engines.

they use the same coil also.

john

swebster · 08-02-2003, 07:45 PM

John,
Thanks for the Harley tip. The thought of a little "chopper" in there really appeals to me! However, the coil turned out to be A.O.K. It actually reminds me of an old Jeep CJ-7 coil. About the size of a can of Red Bull with a connection for each wire and the terminals all on the same end.

swebster · 08-12-2003, 05:59 PM

Just to follow up on the generator issue, it turned out to be a gummed up carb. I managed to find the Onan Operation Guide in the PO's documents and read about checking the needle and float clearances. So I pulled the heat shield and manifold to get the carb out of the generator compartment. Just for fun I decided to remove both needles and spay some Gunk Carb Cleaner into the seats and bowl.

I bolted it all back together, primed the fuel line and it started up right away...a quick choke adjustment and it stayed running from cold start to full load. Since we were getting ready to head back from New Hampshire at this point I changed the oil and filter and fired her up. One air, no problem, two airs, no problem. I did keep blowing the 5 amp ignition fuses until I realized I was putting in the wrong fuses. Got the correct fuse at Napa in PA and she ran the rest of the trip.

Ya - Hoo! So I guess this is normal around here right? I mean, spending your entire vacation, at the beach, with your kids and wife building sand castles while you tinker and tune and get things working on the Airstream. Man this could become a real problem. If this is the support group I'm in deep!

George · 08-20-2003, 05:43 PM

It is wise to remember that "FUN" or "RECREATION" is doing what one enjoys, not what someone says you should do.

I prefer to do what I enjoy, the satisfaction of a problem solved
far outweighs for me, a day sitting on the beach, or playing a ball and stick game.
Enjoy your new found "recreation"
Ol' George

ALANSD · 08-23-2003, 12:48 PM

what about the fuel filter on these Onans? The manual says an external filter is not recommended, the one inside the fuel pump is sufficient. Do we pull out the one in the pump and clean the screen or replace it?
Adding a glass inline before the pump looks to be an easy project.

PeterH-79MH · 08-23-2003, 02:46 PM

Alan, I would leave that pathetic little piece of filter in there, after cleaning it real good with compressed air. The reason is the rubber cap seal. You wouldn't want it to start falling apart and going in the carb.

ALANSD · 08-23-2003, 04:30 PM

ok, I figured on leaving it after a good cleaning, and adding a glass inline before it. NAPA says 3-4 bucks for the filter, seems like good insurance.