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KendallP's avatar
KendallP
Explorer
Jul 27, 2017

1986 Onan BFA 4 - Starts every time, but runs just 5 sec.

So today I finally got around to pulling the top off the carb, including float, needle and spring. But first I started er' up and ran her for a minute or so. But I didn't want to heat her up before taking it apart, so I shudder' down.

Got 'er all put back together after the clean. Verified everything in it's proper place with photos. Went to start her up and...

1. Ran for a few seconds. Probably running on carb and choke cleaner. Bowl was empty. Probably should have put some gas in the bowl before putting the lid back on.

2. Then wouldn't start forever.

3. Sprayed a little carb and choke cleaner in the air cleaner and got 'er to fire up.

4. Now time after time she will start... run beautifully for about 5 seconds and then shut down.

The weirdest part (to my anyway) is what's going on in the clear fuel filter (fairly new, by the way.) It's only about a third full of gas, which bothers me a bit, but what's weird is... when I hit the start switch, I can see gas flowing into it. But after she fires up, it seems to quit. Then 5 seconds later, she dies.

The fuel filter is sitting intake side up. So there isn't any air flowing down into the fuel pump.

Coach currently on shore power.

I need the generator by morning.

Any thoughts?
.

20 Replies

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  • 1995brave's avatar
    1995brave
    Nomad
    Jul 27, 2017
    A test you can try for the fuel pump is take a gas can put a hose into it connected to the fuel pump of the generator. Start the generator and if the filter fills up with gas and the generator keeps running then you have a problem along the fuel line to the tank. By the way most gas tanks have a hose between the tank and the hard line along the framerail. That way the tank can be dropped some to disconnect the lines.
  • KendallP's avatar
    KendallP
    Explorer
    Jul 27, 2017
    1995brave wrote:
    You said you removed the tank lid? Is that the gas cap? If it is and the generator kept running, then I suspect at sometime you replaced the gas cap with a non vented cap and it should be a vented cap.

    Yes. Gas cap. Guess I was tired.

    Turns out that wasn't likely the problem. I even added 9 gallons of fresh gas I had in the yard, thinking, perhaps the slight angle I was parked on made half a tank look like low fuel to the genny. But now it's got 3/4 of a tank and still a problem.

    I don't know the expected service life of a fuel pump, but I don't know that this one has ever been replaced. I would have to check the log. But if it has, it would have been at least 15 years ago.
  • KendallP's avatar
    KendallP
    Explorer
    Jul 27, 2017
    j-d wrote:
    A bad fuel pump is always a possibility. There's probably a generic replacement that bolts right in. We had a BFA and I replaced ours with a little Purolator generic. There are "Standard (sometimes called High) Pressure" ones 5-7 PSI and "Low Pressure" more like 3 PSI. BFA calls for "Low" and it worked fine.

    Do you have a Service Manual for BFA? I kept mine, and can scan the troubleshooting pages for you if you like. PM me with your email ID.

    I do have a service manual, but thank you much for the kind offer.

    Now to see if anyone local actually has that replacement in stock! Wish me luck.
  • KendallP's avatar
    KendallP
    Explorer
    Jul 27, 2017
    Well so much for that. The morning after... same, basic trouble.

    When she's got fuel, she runs smoothly. But with no load, she hunts every now and then. It seems clear that the cause is fuel supply.

    I added the A/C load and... same thing. She took on the load, but surges every 10 seconds or so. I watched the fuel filter and it looks like the same thing. When she's surging, you can see the gas pour in. But when she goes back to smooth... the fuel seems to stop... and... if I recall correctly... even bubble backwards... as the filter is still only about a third full.

    I have not run down all the lines, but I'm guessing they are steel. So the likelihood of an issue there, I believe, is low. And there don't appear to be any kinks between the filter and the steel, which is only about a foot-worth of rubber hose.

    Pump seems the most likely candidate at this point.
  • 1995brave's avatar
    1995brave
    Nomad
    Jul 27, 2017
    You said you removed the tank lid? Is that the gas cap? If it is and the generator kept running, then I suspect at sometime you replaced the gas cap with a non vented cap and it should be a vented cap.
  • garyemunson's avatar
    garyemunson
    Explorer II
    Jul 27, 2017
    Hope that fixes it! Older RVs can have a problem with the generator fuel line rubber. Usually the factory chassis fuel lines are resistant to alky but the hoses that the RV mfgs use for the genny feed can be cheaper stuff that modern gas attacks.
  • j-d's avatar
    j-d
    Explorer II
    Jul 27, 2017
    When it's in Start Mode, the Control Unit bypasses safeties like oil pressure and checking for output. When you release the switch into RUN, Control starts sniffing around for problems. I suspect it's either

    1. Finding something actually wrong, and protecting you from the consequences or

    2. Keeping you from having A/C because it thinks something's wrong that isn't

    A bad fuel pump is always a possibility. There's probably a generic replacement that bolts right in. We had a BFA and I replaced ours with a little Purolator generic. There are "Standard (sometimes called High) Pressure" ones 5-7 PSI and "Low Pressure" more like 3 PSI. BFA calls for "Low" and it worked fine.

    Do you have a Service Manual for BFA? I kept mine, and can scan the troubleshooting pages for you if you like. PM me with your email ID.
  • KendallP's avatar
    KendallP
    Explorer
    Jul 27, 2017
    .
    ***EDIT*** Next morning... same trouble. So the post below is now obsolete.



    Yeah, I figured the fuel pump could be acting up.

    Oil level dead on.

    So after some more searches, I came across the obvious ideas of low pressure in the gas tank or a kinked supply line or some other supply issue. So I took the tank lid off. Then went around and noticed the filter was nearly full. So I started 'er up and she ran and ran. BUT... the fuel filter was dropping fast and would just maintain above empty while fuel was coming in.

    So I looked underneath the rig and the rubber line appeared a bit kinked where it met up with the steel. I straightened it out and so far so good!

    Fingers crossed, prayers said, rabbit's foot and Buddha belly rubbed, etc. etc...

    Dry camping tomorrow. Supposed to hit 100. Some A/C sure wouldn't hurt.

    Thanks!
  • darsben1's avatar
    darsben1
    Explorer
    Jul 27, 2017
    Are we sure the oil level is okay? Genny has a low oil shut down that kills genny if no oil pressure sensed.

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