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gglenn

Monaco Diplomat -Fuel Flow (2004 ISC 8.3L, 330hp)

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Had this on a personal thread but thought I would share, hopefully may help others.

My system is a CAPS II, which has a common rail for high pressure fuel, ie the Gear/High pressure pump does not have 6 individual lines to each injector.

Coach has a Cummins ISC 8.3L 330hp questions, (Engine S/N 46386599), , quickserv info. for my specific engine says it's a CAPS II.

So, I've edit my original post into more of a statement than a question, please see later post with Cummins Common Rail fuel flow info. attachment
 
Having some recent stalling/engine stop, no start problems. Luckily it was at the house!  Many online, say it's the lift pump! None of the forums describe if the "lift pump" is the what I consider the prime pump or possibly the "lift pump" is a section of the CAPS II pump.  Anyway, trying to "fix" this myself and decided to ADD an AirDog II 4G into the equation and remove the prime pump behind the ECU cooler, could be a good plan or possibly unnecessary.   Figured it was cheaper than a tow and a Cummins bill.
 
AirDog is basically a inline pump with it's own primary/secondary filter, and also removes "air" from Fuel, no magic magnet thou.
 
Fuel flow: (Please reference attached pdf file with pics)
Line 1: Tank to AirDog in side compartment on RV, Monaco relocated both Primary/H2O separator and Secondary to side compartment.  I chose to put AirDog in place of the original primary.
Line 2: Airdog to rear of engine fuel manifold/port
Line 3: rear of engine fuel manifold/port to ECU Cooler Port In
Line 4: ECU Cooler Port Out to CAPS II (Gear Pump!),  #19 on diagram
Line 5: CAPS II (Gear Pump!),  to Secondary filter
Line 6: Secondary filter to CAPS II (High Pressure portion), into #16(#2 port). 
Fuel returns from rail to back of engine fitting/ fuel manifold to enter into fuel inlet flow/return to tank.
 
I've removed the prime pump (only ran for 30 seconds on key on) that was behind the ECU Cooler (see below), it was plumbed in parallel with the ECU cooler.  I believe it's stock purpose was only a "prime" and then after engine was running, fuel is "sucked" thru fuel system via. CAPS II (Gear Pump!),  .  Since adding AirDog, I figured it was unnecessary and also had a check valve (ECU Cooler IN) that caused issues for some.  Removed Check valve also.  Hopefully I don't have hard starts without check, AirDog hopefully offsets that issue.
 
PS 5 separate hose (Line #2-#6) sections with 12mm to Push Type 1 connector, Push Type 2 connector 2, and Banjo fitting have been replaced with 12mm to #8 JIC male end and #8-1/2 hose/fitting.  Old hose was a mix hard plastic, some was rubber.
 
DickandLois Reply:
 
Gglenn, Just took the time to look at threads that cover you engine and some fuel issue. You have been reading the, but the second link is in a different thread first one and might prove helpful.

http://community.fmca.com/topic/7186-cummins-isl-and-isc-engines-with-caps-fuel-injector/?page=2

http://community.fmca.com/topic/9625-cummins-caps-system-redesign/

I will be reading your information over the next few days to see what might be helpfull.

Rich.

More from me.

He's doing something very similar to my plan other than he is putting the pump up front at the tank vs. just behind the rear tire bay in my plan.  So, my plan AirDog will have to work "harder" in a prime or filter change situation, but it's also designed for a tough life.  Much more robust design than the stock "lift" pump.  Diagram shows the 2 separate "pump" areas in the single unit, the plumbing runs to in the CAPS II pump; ie  one IN/OUT (7, 9 in diagram), (This is the Gear pump) which is also before the secondary filter and one IN to the high pressure pump unit at the end of the fuel loop (11 in diagram), after secondary filter. (This is the high pressure pump)  13 is the high pressure out to rail.

The lift pump is a separate unit, runs for about 30 seconds on key on, I will call it a prime pump.

So, the stock pumps are Lift Pump, Gear Pump, then High Pressure Pump. Lift pump is the small cylindrical pump behind the ECU cooler, Gear pump and High Pressure are in the same upper unit.

Found these attached pics on quickserve.  Gives the Fuel Flow path on the standard cummins config, obviously this gets tweeked when placed in the various coaches. Diagram is hard to read, but the text (see attached) shows each part of the fuel path.

CommonRail_Fuel1.JPG

 

DickandLois Reply:

The Diesel fuel is used to cool the injector pump, so more fuel is supplied then used. The Fuel tank acts as a heat sump, that removes heat by spreading it out in the fuel before it is recycled through the engine again. NOTE ! As the fuel is used the ability to cool the fuel is always decreasing.

The key to maximum fuel economy is a fuel tank that is half full in hotter temperatures. Cool fuel increases MPG 

what pressure range? Do not work around a diesel engine with a possible high pressure leak when running.

Clean the area well, start the engine, stop after a few seconds where is the area wet with fuel - that is the general location of the leak. The pressure are high enough to cut off a finger or kill if the wrong area is exposed to these pressures.

Cummings engines, deliver around 18,000 psi of pressure.

The Bosch VP44, which is able to produce 23,000 psi of pressure.

 

*In today's diesel engines, fuel leaves the injector at 30,000 psi.

Note. The ISC fuel return line(s) run under the valve cover and do leak at times, this will make the engine appear to be making oil as the fuel mixes with the engine oil. Not Good !!

ISC is a real good engine over all, but like I said it does have its weak points.

 PS 5 separate hose (Line #2-#6) sections with 12mm to Push Type 1 connector, Push Type 2 connector 2, and Banjo fitting have been replaced with 12mm to #8 JIC male end and #8-1/2 hose/fitting.  Old hose was a mix hard plastic, some was rubber. 

Good plan - the OEM hoses do not like the Bio fuels.

Keep all in the loop, Rich

 

 

Cummins_AirDog_CAPSII_ECU.pdf

Cummins_CommonRail.pdf

Lift pump move.pdf

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Glenn, The real proof will be down the road in different conditions and with the differences between your approach and Joe's. There is a good potential for some over the road base information to compare the two thoughts of how to resolve some of the OEM issues.

Think all will benefit from future posts! 

Glen posted hear and Joe posted his approach on this thread.

 

 

A number of the members have mentioned how much they enjoy the information. I must admit that for me it fuels my insatiable curiosity and the issues always keep my mind challenged. 

Hopefully the forum's format helps new owners and keeps the longtime owners engaged in the challenges of owning a house on wheels and the good friendships that also lead to some good fun when our paths cross.

Rich.

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Be aware that the Cummins system is designed to work under a slight VACUUM (i.e. to suck fuel from tank to pump).  I am not aware of any data from Cummins on the effect of supplying positive pressure where the system was designed to work under  slight vacuum. 

Absolutely agree-- too much restriction can certainly cause issues-- whether in tank fuel pickup,  hose length and/or diameter, hose routing, restriction in primary fuel filter and/or secondary fuel filter.

From Cummins document 018-016: Fuel System

For CAPS Fuel System:

Maximum fuel inlet restriction at rated HP measured at lift pump inlet: 4" HG.

Maximum fuel inlet restriction at rated HP measured at CAPS pump inlet: 10" HG.

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Back to defining differences between CAPS, CAPS II, and HP..systems in terms of # pumps involved.

To restate: My CAPS II stock is lift/prime pump, gear pump, and then high pressure pump. Redone is AirDog II4g, gear pump, and then high pressure pump.

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OK,

 

Finally got this project finished up and need your thoughts on a ECU code.  So, the stock "lift/prime pump" has been removed from the system, so connector is disconnected from ECU harness.  The Engine code is 2265, which is Lift Pump High/Low voltage.  So, ECU is expecting a load from lift pump for 30 seconds and doesn't get that.

So, any thoughts on a Bypass harness.  Maybe will need ECU tweek if possible.

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Glenn, you need to trick the ECM into thinking your OEM lift pump is still connected. Its simple to do, I bought an extension harness on the web plugged it into the existing power feed to the OEM pump, routed it into my electrical bay, I use that to energize a relay that is NOT connected to anything. That is all the ECM needs to see is resistance within the relay coil and it assumes the fuel pump is operating properly.

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Glenn, since you are stalling is it safe to say this is happening after the lift pump shuts off? What are your fuel lines made of?

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Sorry we had some discussion in Private.  So to catch you up, AirDog is now installed in place of remote Primary filter, AirDog has Primary/Secondary on it, all stock lines and fittings after it have been replace with 12mm to #8JIC, Push on style #8-1/2" JIC fittings/hose used. 5 separate hose sections replaced.  Stock secondary filter after Gear pump still in place.  Stock hard Nylon Tube from Tank to AirDog left as is.  Stock lift/prime pump behind ECU cooler removed, was in parallel loop with ECU Cooler.  AirDog is now lift/prime pump, running always vs. 30 seconds.

Reading in service documents Gear pump outlet in stock setup is about 20 psi at idle, Airdog pressure set similar, which yield same 20 psi pressure at inlet of Gear Pump).  Stock Gear pump inlet would normally be in a vacuum (10" max), less vacuum good, more than 10" vacuum bad.  AirDog puts Gear Pump inlet at approx. 20 psi. vs. in a vacuum.  Once engine RPM is above idle Gear Pump pressure increases, approx. 70psi at high idle, more psi higher RPM.  High Pressure pump is after all this.

It's running great now, but a real road test and time will confirm if the upgrade was worth it.  AirDog is easily serviceable and I have a dummy light for low Fuel pressure,  no more guessing.  I may add a Fuel pressure gauge, so I know exactly what is going on with pressure as Filters get dirty, under load pressure, etc.

 

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Jleamont, Just read your second post about Relay trick.  So, you have no constant 12v on the Power side of relay and are using the Lift pump +12v to "fake activate" the Relay or are you using the lift pump +12v and -12v on the Power side of relay?  Hopefully asked that properly.  Wiring schematic sketch?

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Glenn, I have the OEM fuel pump power and ground going into pins 85 and 86 on a relay similar to the one in the photo. All it does is close the relay when the ignition is turned on, the ECM sees the current draw and it's satisfied. I had an old fog lamp relay in my tool box laying around, that is what I used. Just to be clear there is no load connected to the relay, it just switches internally and the ECM is happy.

 

70198785.jpg

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I like it!   Thanks much. I may just create a short lead off old lift pump harness, add Relay and zip tie it down at existing location.  If any problems with it in the future would be more obvious (no wire tracing) troubleshooting.  Likely I can find a sealed Relay setup.

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I bought a Dodge truck (Cummins powered) fuel pump relocation harness and cut the end off that was supposed to plug into the fuel pump, it was nice and clean with the proper weather pack connector. I wanted to get the relay out of the engine bay and put it with all of the other stuff.

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Glenn, are you sure you have the CAPS system? The diagram above shows a Common Rail design, which would be correct for your year unless you have an older engine (which is possible and not unheard of).

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In Quickserve for my engine S/N they call it a CAPS II.  Seems no one can tell me if CAPS II is really just another name for High Pressure Common Rail.  I must assume with HPCR that each injector get the high pressure from the Common Rail Fuel manifold vs. the older style that has pump supplying high pressure separately each injector.  My pump DOES NOT have 6 individual high pressure lines to each injection.

When I was getting filters at Cummins NW, I asked the parts guy about that Pump when he was in QuickServe and he commented that I had the better pump design.  Other versions were more problematic.

 

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Just to confirm I'm not looney, these guys that sell reman. pumps call it CAPS II.. You can see the two red shipping caps on the bottom area, this is the Gear Pump IN/OUT.  Harder to see the single High Pressure out port, but it's up top.

I believe I never stated I had a CAPS setup, tried stating CAPS II.  Seems everyone wants to lump them into being the same design.

CAPS II.pdf

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48 minutes ago, gglenn said:

I have no idea what the "proper" name for it is.  In Quickserve for my engine S/N they call it a CAPS II.  Seems no one can tell me if CAPS II is really just another name for High Pressure Common Rail.  I must assume with HPCR that each injector get the high pressure from the Common Rail Fuel manifold vs. the older style that has pump supplying high pressure separately each injector.

When I was getting filters at Cummins NW, I asked the parts guy about that Pump when he was in QuickServe and he commented that I had the better pump design.  Other versions were more problematic.

 

Gene, been consulting with Joe. Because at this point I'm totally confused. There are items in the system that need to be there to prevent drain back. Joe is using the OEM style Lift Pump and our concerns are that the Pump you want to install could cause issue, with too much pressure and cause the pump to fail. 

This is a copy of his response to the File information you attached and I have been trying to pull all the info together.

 

What's confusing to me is he has an ISC but it has the same CAPS Pump as I do (due to the HP of the engine, he is not equipped with the VP44 Bosch, or shouldn't be over 300 HP). So the fuel diagram he posted is not his design, not even close. He attached a Cummins service Bulletin to relocate the lift pump on the ISB, again not even close to his design.

If he pulled a check valve out of the system he is liable to send too much back to the tank and starve the CAPS pump.

I have a one way check valve on my supply line that I put in, only so when I turn the key on there will always be fuel sitting there and the pump isn't ever dry. I had to do this when I removed the factory primary filter and housing since it had the one way check valve built into it, now with the Davco primary I lost the check valve and had to make my own.

Rich.

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As we say...Clear as mud!

Obviously we have various fuel "pump(s)" versions on our similar engine, so yes it's a bit confusing between the three of us.

Yes, it is possible that my AirDog could cause pressure related problems/failure in either the Gear pump or the high pressure pump.  I'm betting not, time will tell.  As I stated in other post, I believe the biggest pressure impact will be at idle, once off idle pressures after gear pump will likely be similar to the stock system.

As far as the fuel flow picture and sections I posted, it's accurate other than the relocation of the filters by Monaco.

ISB Lift pump relocation document was in my quickserve area.  The main issue for stock relocation was to get it off the engine, I was just referencing a common problem on the ISC, but document shows title as ISB, so guessing same issue on both. 

The check valve I removed may cause drainback, or loss of initial pressure when engine is off, but when engine is running it served to isolate/separate the lift pump and ECU cooling loop and likely stop drainback.  If I have problems with drainback/hard starting I will add an inline check at the AirDog IN port, easy addition in my setup.

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