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04 Neptune ISB 300 Cummins fuel pressure issue.re


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Hello and great to find this site for some help with a head scratcher? Have a Cummins 25 15 fuel delivery pressure code and the symptom is engine stumbles or misses under load when driving, but not so much in neutral?

Engine starts fine, idles and revs in neutral but will stumble badly going thru gears driving. My mechanics scan tool shows only about 1000 Bar pressure at 1500 rpms and he believes that is low. Pressure pump is rated to 1600 Bar pressure.

Also when we checked for fuel pressure at top of filter head there was zero lbs yet when switched to vacuum pressure gauge it showed 15 inches at idle.   Mechanic believes there is no engine mounted lift pump altho Cummins said based on my serial no. there is one that should run for 30 seconds and then shut off allowing fuel to pass thru.  Problem is cant hear anything running with key on and there isnt any pump between water filter, ecm cooling plate, main filter and pressure pump. 

Based on my serial # Cummins shows lift pump # 3968187, but all we see on engine is  pump # 3964407 and it is gear driven not electric. Engine serial # is 57165940.  Very confusing based on what Cummins tells us. 3964407 pump is low on curbside of engine. Could it be the lift pump and pressure pump is hiding on driver side of engine or?  Pic attached is of only pump found.

Did Monaco put  a transfer pump intank and say nothing about it in my manual?  Or is vacuum pressure from pressure pump all it takes to run motor?  We've changed out both filters and no leaks visible to allow air in.

This saturday we are going to tap into filter head with fuel line and remote gas tank to see if stumbling solved.

Any ideas greatly appreciated and if more info needed glad to add. 

Crazy thing is how engine starts instantly and even high idles fine yet shows no fuel pressure like would expect from lift pump?

If rig has intank pump which fuse panel would it be powered from to check that before dropping tank?  What might its fuse or relay be called?

Sorry for huge first post, but as can see weve done lot of research troubleshooting this. So sad that all chassis diagrams lost in the Monaco fire  Thanks for any help. Greg W

 

20210204_130553.jpg

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If your engine is a 24 valve one the early models has the electric pump mounted on the engine, later years they were either  mounted in or close to the fuel tank, depending on chassis manufacturer.

My brother in law has a similar problem the had low voltage at the fuel pump, found problem to be corrosion on fuel pump inline fuse holder.

Jim

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Jim B, thanks for the reply, would you know the range of years for engine mounted pumps versus frame or intank lumps, or a source that might?  Strange that my 400 page manual only dicusses the two fuel filters and the complex sending unit in the tank?   No mention of  any lift or transfer pump even tho doesnt appear to be one on the engine. If was on the engine would make sense that Cummins all the help I need. Thanks

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11 minutes ago, Greg W said:

Jim B, thanks for the reply, would you know the range of years for engine mounted pumps versus frame or intank lumps, or a source that might?  Strange that my 400 page manual only dicusses the two fuel filters and the complex sending unit in the tank?   No mention of  any lift or transfer pump even tho doesnt appear to be one on the engine. If was on the engine would make sense that Cummins all the help I need. Thanks

The 12 valve engines had mechanical fuel pumps.  I believe all of the 24 valve engines have electric fuel pumps.  The first 24 valve engines were seen in motor homes around the 1999 model year. The electric pumps run continuously on these engines, when they completely fail you  are dead in the water.

On the early 24 valve engines the electric fuel pumps were located on drivers side of the engine.

Jim

Edited by Jim Byrd
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Thanks Jim, on my 04 ISB 300 cummins it starts instantly and sounds fine even tho 0 fuel pressure at filter head.  Does have 15 inches of vacuum pressure tho. How can engine even start if electric pump is down yet dont hear a sound when key on? Real head scratcher!  

In 04 could electric pump still be on drivers side of engine rather than intank.? Drivers side of engine has turbo, oil filter and alternator.

Followed fuel lines along frame and see nothing?  

Today we tapped into the top of the fuel filter head and installed a fuel line to a boat fuel can to bypass the fuel system.   Fired right up and no 25 15 fuel pressure code.  Great test drive, good power and most importantly, no stumbling or lurching!  

So high pressure pump is good.  There is an air leak or partial blockage in the fuel line somewhere that we bypassed, or an intank electric pump has failed and fuel system starves for fuel under a load even tho engine starts and idles?

Really hope someone here can help wade thru this problem between the ISB 300 Cummins and an 04 Monaco. 

Did Monaco put a pump in tank but show nothing in manual ,and altho Cummins claims there's an electric lift pump that shuts off after 30 seconds we can't see or hear anything and no fuel pressure, yet runs!?!?

How about it Bill D or others with good knowledge of  Cummins and Monacos systems? Is there a secret electric pump in the tank? Thanks 

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41 minutes ago, Greg W said:

 

Thanks Jim, on my 04 ISB 300 cummins it starts instantly and sounds fine even tho 0 fuel pressure at filter head.  Does have 15 inches of vacuum pressure tho. How can engine even start if electric pump is down yet dont hear a sound when key on? Real head scratcher!  

In 04 could electric pump still be on drivers side of engine rather than intank.? Drivers side of engine has turbo, oil filter and alternator.

Followed fuel lines along frame and see nothing?  

Today we tapped into the top of the fuel filter head and installed a fuel line to a boat fuel can to bypass the fuel system.   Fired right up and no 25 15 fuel pressure code.  Great test drive, good power and most importantly, no stumbling or lurching!  

So high pressure pump is good.  There is an air leak or partial blockage in the fuel line somewhere that we bypassed, or an intank electric pump has failed and fuel system starves for fuel under a load even tho engine starts and idles?

Really hope someone here can help wade thru this problem between the ISB 300 Cummins and an 04 Monaco. 

Did Monaco put a pump in tank but show nothing in manual ,and altho Cummins claims there's an electric lift pump that shuts off after 30 seconds we can't see or hear anything and no fuel pressure, yet runs!?!?

How about it Bill D or others with good knowledge of  Cummins and Monacos systems? Is there a secret electric pump in the tank? Thanks 

If I were a betting man, i say the fuel pump was in the tank.  you should be able to trace the wiring to the top of the the fuel tank. If the pump is in the tank you should find several wires going in the tank.

I lead you wrong on the location of the fuel pump is on the engine, it would be on the opposite of the exhaust and turbo. I was think of location in a Dodge Ram.  Before I was too eager to drop the tank you need to locate the fuse for the fuel pump,  On my 04 Holiday Rambler with an 8.3 ISC Cummins, it't located in the battery compartment. In my rig there are in-line fuses and they aren't very well labeled.

Jim

 

Jim

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10 hours ago, Jim Byrd said:

If I were a betting man, i say the fuel pump was in the tank.  you should be able to trace the wiring to the top of the the fuel tank. If the pump is in the tank you should find several wires going in the tank.

I lead you wrong on the location of the fuel pump is on the engine, it would be on the opposite of the exhaust and turbo. I was think of location in a Dodge Ram.  Before I was too eager to drop the tank you need to locate the fuse for the fuel pump,  On my 04 Holiday Rambler with an 8.3 ISC Cummins, it't located in the battery compartment. In my rig there are in-line fuses and they aren't very well labeled.

Jim

 

Jim

Thanks Jim,   if pump is in tank just hard to believe no mention in manual?  Is it possible Monaco specd no lift pump because isb300 is smaller so the vacuum pressure from the pressure pump is sufficient?

Tank is up against floor of coach and hard to see much but did find one can size bulkhead with wiring.  Reading about complex sending unit made me think thats it, but better do more thorough check.

Fuse panel in battery box vaguely labeled and will check some in line fuses too.

Read here Bill D worked extensively with Monaco techs for years. Does he reply to posts  or do I need to contact him directly? Thanks again.  Greg W

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Never heard of a Monaco with a fuel pump in the tank.    Monaco used an elect lift pump, mine is mounted on the engine ( pass side ).   My lift pump runs for about 30 sec,  after that the high pressure injection pump sucks the fuel all the way from the tank . Both pumps use suction that is why you have vacuum at the filters.                      I have read that the ISB lift pump runs all the time.   

You had no way of knowing but Bill D died a while back the Monacoers forum is now owned by David Pratt                                                  

 

Edited by Ray Davis
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33 minutes ago, Ray Davis said:

Never heard of a Monaco with a fuel pump in the tank.    Monaco used an elect lift pump, mine is mounted on the engine ( pass side ).   My lift pump runs for about 30 sec,  after that the high pressure injection pump sucks the fuel all the way from the tank . Both pumps use suction that is why you have vacuum at the filters.                      I have read that the ISB lift pump runs all the time.                                                      

 

You are correct, the ISB electric fuel pump run continuously and is the only low pressure fuel pump.  The fuel system is the same as use on like years of the Dodge Ram trucks. 

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47 minutes ago, Jim Byrd said:

You are correct, the ISB electric fuel pump run continuously and is the only low pressure fuel pump.  The fuel system is the same as use on like years of the Dodge Ram trucks. 

Thanks guys and RIP Bill D,

Where is the lift pump found on pass side? Doesnt seem to be behind ecm cooling plates as have read? Great news that same as dodge in those years. 

Fuse box in battery box very vague! Ideas on fuse and relay locations? 

1 hour ago, Ray Davis said:

Never heard of a Monaco with a fuel pump in the tank.    Monaco used an elect lift pump, mine is mounted on the engine ( pass side ).   My lift pump runs for about 30 sec,  after that the high pressure injection pump sucks the fuel all the way from the tank . Both pumps use suction that is why you have vacuum at the filters.                      I have read that the ISB lift pump runs all the time.   

You had no way of knowing but Bill D died a while back the Monacoers forum is now owned by David Pratt                                                  

 

Thanks Ray and rip Bill D,   glad to hear may not be dropping tank. Haha. 

Where is your lift pump found on pass side?  Doesnt look like theres a pump behind the ECM cooling plates and cant hear anything running?

Can only find pump # 3964407 pressure pump on pass. 

Thanks and sorry for redundant posts, but big fingers on little phone. Haha 

 

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25 minutes ago, Greg W said:

Thanks guys and RIP Bill D,

Where is the lift pump found on pass side? Doesnt seem to be behind ecm cooling plates as have read? Great news that same as dodge in those years. 

Fuse box in battery box very vague! Ideas on fuse and relay locations? 

Thanks Ray and rip Bill D,   glad to hear may not be dropping tank. Haha. 

Where is your lift pump found on pass side?  Doesnt look like theres a pump behind the ECM cooling plates and cant hear anything running?

Can only find pump # 3964407 pressure pump on pass. m

Thanks and sorry for redundant posts, but big fingers on little phone. Haha 

 

The part # that you listed is the hi pressure pump. You could  start from the fuel tank and follow the fuel line to the engine to see if you can find the electric pump.  Since your rig is 04 I'm still thinking that you will find it in the take, my reasoning is based that by this time that's were Dodge Rams were placing them.

The fuel pump location may be a mystery. The chassis manufactures deliver them to the RV manufacturer as a drive-able unit, I know the fuse on my brother-in-laws 04 Holiday Rambler with the same engine is located in the battery compartment and they are poorly labeled and the wiring is a rats nest,

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Thanks Jim B for this valuable info. Do you think brother in law may know where his lift pump may be? Side of engine or tank?   Inline fuse or in fuse block?  Has he dealt with this same issue?

Pushing fuel is easier than pulling so may have moved pump to tank. Monaco built their own chassis tho, so bet Cummins came in a box?  Thanks Greg  W

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1 minute ago, Greg W said:

Thanks Jim B for this valuable info. Do you think brother in law may know where his lift pump may be? Side of engine or tank?   Inline fuse or in fuse block?  Has he dealt with this same issue?

Pushing fuel is easier than pulling so may have moved pump to tank. Monaco built their own chassis tho, so bet Cummins came in a box?  Thanks Greg  W

Actually I have 2 brother-in-laws with coaches that have the 5.9 ISB,  The one with a freight liner chassis (1999 freightliner chassis  has the fuel pump is mounted by the ECM and he got towed in twice because of fuel problems (low voltage to fuel pump) His fuse is in battery compartment was found corroded. 

The other one just purchased his (04 Roasmaster chassis) and has had no problem and hasn't had need  to locate fuel pump, he did look for fuse location and he couldn't find in manuals, manual did state that additional fuses were located in battery compartment. He did locate several in battery compartment and he believes they are engine related, because one was clearly identified as ECM, other ones were not readable.

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I have a 2001 Diplomat with the ISB 300 Cummins and had this same issue around three years ago. On mine, the coating treatment intended to protect the inside of the fuel tank had peeled over time and clogged the fuel line that feeds the lift pump. This is an electric pump located just ahead of the high pressure injector pump (top passenger side of engine). Had to remove the fuel tank and sandblast the inside gaining access through the opening for the fuel gauge sensor and another opening on the bottom of the tank. The fuel lines to and from the rear engine and the lines to the generator on the front were also replaced. This was an interesting two week project. The fuel tank, once on the ground, would not clear coming out from underneath without lifting the coach. 

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3 minutes ago, Ray Davis said:

Greg,  There doesn't seem to be very many owners on here with ISB engines.

Our Knight has an ISB 5.9 260 hp. It has an electric lift pump mounted on the passenger side, low rear of the engine.

I have no way of telling whether it continues to run when the engine is running. But I do know that when I use it to prime the fuel system after changing the fuel filters it only runs for less than 30 seconds. Typically I have to repeat that cycle several times before the engine will start.

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2 hours ago, Jim McGarvie said:

Our Knight has an ISB 5.9 260 hp. It has an electric lift pump mounted on the passenger side, low rear of the engine.

I have no way of telling whether it continues to run when the engine is running. But I do know that when I use it to prime the fuel system after changing the fuel filters it only runs for less than 30 seconds. Typically I have to repeat that cycle several times before the engine will start.

Thanks, what year is your coach Jim?  Do you hear the pump when its running? Hearing by year of my coach, 2004  monaco may have switched to intank lift pump?

Going to do priming test at secondary filter head and see if pumps fuel out with key on. Will tell me if lift pump working.  Already have remote tank hooked in there and it ran great, so will be easy test.  Separate hose at bubble primer, hold it in the tank and turn key on. 

Thanks for Irv2 link Ray.  Greg W

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9 hours ago, Greg W said:

Thanks, what year is your coach Jim?  Do you hear the pump when its running? Hearing by year of my coach, 2004  monaco may have switched to intank lift pump?

Should have been visible in my signature block. It is a 2002. I can just barely hear the pump run from the driver's seat with the bed and engine cover up; it is easy to hear from the bedroom.

To prime the system after a filter change I have to turn the key to tap the starter, then the pump will run for 20-30 seconds and stop. Then I need to turn the key off for about 10 seconds before another attempt. It typically takes several attempts before I can start the engine.

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2 hours ago, Jim McGarvie said:

Should have been visible in my signature block. It is a 2002. I can just barely hear the pump run from the driver's seat with the bed and engine cover up; it is easy to hear from the bedroom.

To prime the system after a filter change I have to turn the key to tap the starter, then the pump will run for 20-30 seconds and stop. Then I need to turn the key off for about 10 seconds before another attempt. It typically takes several attempts before I can start the engine.

Thanks, cant hear pump run even if lying under coach so wondering if may have moved pump to tank between 02 and 04?

Doing prime test only to see if any lift pump working at all.  Filled filters when changed them and never lost prime which is nice.

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For what it's worth, Cummins replaced my electric lift pump twice when I owned my '06 ISB 300hp in my Vacationer.  Mine displayed the same symptoms as yours. It would start and idle but bucked and stalled under load.

As others had said, I doubt if it in the tank.  Mine wasn't but I never inquired about it's exact location.  

Also, the fuel delivery system and high pressure pump had nothing in common with Dodge trucks.  The high pressure pump, like you mentioned is mounted to the engine side of the bell housing and is driven by the flywheel. Dodge trucks used a VP series pump mounted near the front of the engine.

 

My suggestion is to perhaps find another mechanic more familiar with the engine and chassis setup. It may not be a Cummins part either.  It may have been a pump installed by the Monaco Chassis shop.  I think you the reason you can't hear yours run is that it has failed.

Bruce LaHargoue

Former owner, '06 HR Vacationer 34PDD, Cummins ISB

 

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6 hours ago, blahargoue said:

For what it's worth, Cummins replaced my electric lift pump twice when I owned my '06 ISB 300hp in my Vacationer.  Mine displayed the same symptoms as yours. It would start and idle but bucked and stalled under load.

As others had said, I doubt if it in the tank.  Mine wasn't but I never inquired about it's exact location.  

Also, the fuel delivery system and high pressure pump had nothing in common with Dodge trucks.  The high pressure pump, like you mentioned is mounted to the engine side of the bell housing and is driven by the flywheel. Dodge trucks used a VP series pump mounted near the front of the engine.

 

My suggestion is to perhaps find another mechanic more familiar with the engine and chassis setup. It may not be a Cummins part either.  It may have been a pump installed by the Monaco Chassis shop.  I think you the reason you can't hear yours run is that it has failed.

Bruce LaHargoue

Former owner, '06 HR Vacationer 34PDD, Cummins ISB

 

Thank you Bruce for most informative reply yet!  Another mechanic friend coming to look tonight and your info will help a bunch. Didnt think had intank pump and even tho lift pump has failed she starts fine but lurches and stumbles driving! Amazing that high pressure pump has enough vacuum to start it. Getting close to solving this.

Thanks to all who have chimed in.

On 2/8/2021 at 5:59 AM, Jim McGarvie said:

Should have been visible in my signature block. It is a 2002. I can just barely hear the pump run from the driver's seat with the bed and engine cover up; it is easy to hear from the bedroom.

To prime the system after a filter change I have to turn the key to tap the starter, then the pump will run for 20-30 seconds and stop. Then I need to turn the key off for about 10 seconds before another attempt. It typically takes several attempts before I can start the engine.

Thanks, cant hear pump run even if lying under coach so wondering if may have moved pump to tank between 02 and 04?

Doing prime test only to see if any lift pump working at all.  Filled filters when changed them and never lost prime which is nice.

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Hey, hey. Found the beer can sized pump hiding behind the ecm cooling plates!

Plumbing to it easy to overlook when tracing lines. Going to test for power to it and go from there .  Move ecm out of the way and should be easy access.

Busy life right now, so may be a bit, but will post up when resolved. 

Thanks all.

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  • 3 weeks later...

Hello, Got her done finally.  New lift pump installed behind the ECM,  primed the system,  fired her up and successful test drive done.  Stumbling and lurching all gone.  Thanks all for advice.  Greg W

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