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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. 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