Holiday Rambler in tank fuel pump quit. Cant find relay?

[Broncorambler]

In tank fuel pump has quit in my 2004 Holiday Rambler Neptune diesel pusher and cant find the fuse or relay for it.
Monaco has identical model rig under different name, but since out of business there are no techs to contact!
Anyone know of a contact who knows these brands well or where might find an electrical schematic to trace down the fuse or relay?
Hope to avoid dropping tank if can, because scan tool shows no power to the pump. Thanks for any help.

[Broncorambler]

Thanks Ivylog. Can you better explain short hose to check for air? Is leaking hose coupling on top of tank or at filters? Sounds like simple fix.
Love to talk by phone if could get number privately?

[Ivylog]

It’s NOT a bad lift pump which is only used for starting the engine... learned that the expensive $$ way. I had the same problem and by putting a short length of clear plastic tubing ($5 in hose, pipe nipple, & 2 clamps) after changing the lift pump, I could see small bubbles in the fuel with lift pump running and the engine running. A big change in temperature made a fitting (which was tight) at the tank start leaking. Removing the hose and putting back on (not as tight) solved the air getting into the fuel which gave me full power again.

Spend $5 putting a clear hose at a fuel filter to check for air in the fuel system.

[Broncorambler]

Great to hear wont be dropping tank. Haha. Would it run at all if bad lift pump? Hoping clogged vent tube. Wish me luck tomorrow.

[filadelfia]

Sounds like a bad lift pump. As Doug said any Cummins shop can replace not too expensive.
Don 2005 HR Neptune
2006 Jeep Liberty toad

[Broncorambler]

Thanks can certainly test it with cap loose and if runs fine, its the vent.
Simple, thanks.

[oldave]

Have you noticed the tank sucking air when you remove the cap after driving?
If it is the vent you could probably loosen the fill cap and solve the problem
Don't drive like that if the tank is full as it may slosh fuel out.

[Broncorambler]

Wow, thanks guys. Already did both filters so next is to check tank vent for clogging. Amazing that vacuum pulls fuel all that way!
High pressure pump likely ok or it wouldnt idle and run?
Only stumbles under load. Thanks

[oldave]

Doug is right, those wires are for the electronic sender.

Have you changed the fuel filters? There should be 2.
Most problems like yours are filters. Diesel fuel can develop/grow algae,
scum or whatever in the tank and can quickly clog filters.
If you have that you will probably see it inside the primary filter, on top.
It is crazy but the fuel is sucked all the way from the tank, there are after
market pumps that can be used.

[dougrainer]

Broncorambler wrote:
The 300 cummins starts and idles fine. Goes into high idle fine and even revs if not under load. Once in gear with brake set or driving it will stumble, rebound and then stumble again in a cycling way like running out of fuel.

My diesel mechanics scan tool shows no fuel pressure from any aux fuel pump, but it does show vac. pressure from hi pressure pump drawing fuel to the engine. Dont know for certain there is an aux pump, but assuming there is because tank is over 20 feet from the engine and seems should be one. Manual makes no mention of one tho?
On top of tank there are number of wires going thru a portal into the tank and seems like more than needed for sending unit.
Two good diesel mechanics believe Cumminns ISB300 engines have an aux pump, but could they be wrong?
Manual does mention that clogged tank vent can give issues and guess id better check it out, but didnt ghink could be culprit.

Hoping might be some good techs on the Monaco group provuded me, but busy next couple days. Thanks much for replies and advice.

On the Manual I sent you the link to. Go to the Calibrating part of the Fuel tank sending unit. You will see WHY there are more wires than you think is necessary. I was waiting for others to reply. I NEVER saw any In tank fuel pump on a Roadmaster Chassis. The fuel pick up and return is just 4 hoses. The 3rd/4th hose is for the optional Aqua Hot and Genset feeds. The good news is, since the Fuel pump system is part of Cummins, you should be able to get it fixed by a Cummins Service Center. Doug

[Broncorambler]

The 300 cummins starts and idles fine. Goes into high idle fine and even revs if not under load. Once in gear with brake set or driving it will stumble, rebound and then stumble again in a cycling way like running out of fuel.

My diesel mechanics scan tool shows no fuel pressure from any aux fuel pump, but it does show vac. pressure from hi pressure pump drawing fuel to the engine. Dont know for certain there is an aux pump, but assuming there is because tank is over 20 feet from the engine and seems should be one. Manual makes no mention of one tho?
On top of tank there are number of wires going thru a portal into the tank and seems like more than needed for sending unit.
Two good diesel mechanics believe Cumminns ISB300 engines have an aux pump, but could they be wrong?
Manual does mention that clogged tank vent can give issues and guess id better check it out, but didnt ghink could be culprit.

Hoping might be some good techs on the Monaco group provuded me, but busy next couple days. Thanks much for replies and advice.

[oldave]

Are you sure it has a fuel pump in the tank? My Windsor doesn't have that, it
has an electric fuel lift pump mounted on the engine. I can hear it run for
a while when I turn the ignition on.

What sort of trouble are you having?

[Ivylog]

The Cummins engine has a 12V fuel lift pump on the engine ...didn’t find a pump in the tank on page 397.

[Broncorambler]

Thanks Doug, but no fuel pump reference on page 322 I can see?
Do you see something im missing?

Also thanks to poster for Monaco group link!

[Broncorambler]

Thanks for link to manual so have digital and hard copy now. No mention of auxiliary fuel pump in manual though.
Should be able to trace leads somewhere if lucky but many wires bundled together down the frame.