jleamont

Cummins CAPS System Redesign

66 posts in this topic

After some intense research I have decided to modify the existing fuel system design to eliminate the root cause for the CAPS fuel injection pump failure which is low fuel pressure to the fuel injection pump. I spoke to a RV repair facility that has done several of these, the longest running unit has been out for over 7 years and has accumulated just shy of 75,000 miles with no problems. This unit had two previous CAPS pump failures, none since. After doing my research speaking to one ISL owner that modified his I think I am going to tackle this for insurance. Here is my reason; the factory design of the Fuel injection pump pulling/sucking fuel from the tank 40' in front of it through a pump that shuts off after 30 seconds and through two filters is crazy, it strains the pump and it ultimately starves itself causing it to self destruct.

The conversion will give the system a pump close to the fuel tank that constantly runs supplying filtered fuel to the CAPS injection pump so it doesn't starve and will always have fuel coming at it when the ignition is on. My plan is to relocate my primary filter/separator in the fuel tank bay with the pump mounted just after it, pushing fuel down to the engine's secondary filter then onto the CAPS injection pump. All returned fuel will remain as designed by Cummins and be routed from the Cylinder head and CAPS pump back to the tank via the Cummins lift pump that will be there only to serve as a manifold where the returned fuel all meets up to go back to the fuel tank. The factory lift pump will be capped where the original fuel supply lines connect (so the returned fuel does not leak out and its all sealed up) the electrical connection get's unplugged, the connector gets a relay plugged into it so the ECM see's a draw, assumes its the lift pump and doesn't set a fault code or turn the engine light on, I am remote mounting the relay in my rear electrical bay just as if the factory put it there. I will incorporate a electronic fuel gauge into the design for my coach and put it in the dash as if it came that way from Holiday Rambler so I can monitor fuel pressure, when it drops I will know its time to spin new filters on, no more guessing or waiting for it to starve the pump and begin to buck. All parts are on order except any hoses I will have to make up for the installation so far the tally is at $750.00 this will be the most cost effective insurance policy yet for this coach.

CAPS design; ISL,ISM,ISX the lift pump shuts off after 30 seconds (just to prime the system) and relies on the injection pump suction to feed itself with this design you cannot install an aftermarket warning system to alert you of a problem since you only have fuel pressure for the first 30 seconds. There is no ECM strategy to turn the pump on when fuel volume is low, fuel flow is not monitored, in fact the only item monitored is the lift pump if there is an electrical draw, if its working or not it has no idea, it just will cause the $5500.00 injection pump (parts only not labor) to self destruct. 

ISB and ISC; the ECM will regulate the lift pump and send fuel to the Injection pump as needed. The ECM on these will often not supply enough fuel to the injection pump causing them to fail or the lift pump just fails and you might not realize it since the injection pump will also pull fuel to itself, just not enough. BD diesel makes a kit with a dash mounted alarm incase fuel pressure drops below 5 psi, so you have a chance in saving yourself the cost of an injection pump replacement.

If you have any questions feel free to ask, I have so many notes and diagrams for My ISL engine bay layout I feel like a Cummins engineer that actually did his or her job :o.

 

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You have done a lot of research. Here are some "thinking out loud" things.  Please do NOT take them as "Brett knows this is right/will work." I have NOT researched the issue, but agree with you, fuel system on DP do leave something to be desired.

With your modification, I see no reason to mess with the current lift pump-- it will have an easier job now, but no harm in duplication.

Be sure to spec the new pump for the correct (both): PSI and volume. Both are important.

With those caveats, I like your thinking.

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Brett, thank you for the response and I understand, I am glad you responded! When I spoke to Cummins and asked them if I could send positive pressure into the existing lift pump they told me absolutely not. Something is weak inside, they wouldn't elude to what but the weak link is on the inlet side (I pried), I believe the check ball is plastic and will break apart and go through to the next filter. I would love to see a cut away of that pump.

The CAPS pump will accept up to 25 PSI (per Cummins), what it doesn't need it will return to the tank with no problems. The pump I ordered is the same one the RV dealer I spoke to swears by (I didn't want to be the test pigeon), its adjustable and the factory setting is 17PSI. I spoke to an injection pump rebuilder that is local, he bench tests the CAPS pumps (on the larger engines) at 25 PSI for an integrity test. Since the factory lift pump supplies 7 psi and the CAPS needs 10 minimum for proper lube and cooling...... which baffles me since there is no PSI coming to it now, its just volume that no one including Cummins has a spec on record.

New pump link;

http://www.fassride.com/detail/diesel-fuel-pumps/adjustable-diesel-fuel-pumps/adjustable-dodge-ram-cummins/adjustable-fuel-pump-95-gph-dodge-cummins-1998-1999-2000-2001-2002-2003-2004.php

I thought about building a manifold to connect the return lines (one from the head, one from the CAPS pump and the 1/2" hose that actually feeds the tank) but the more I thought about it...I already have it. So two 5/8 JIC female plugs for the lines and I am done. Since I changed that pump in 2014 those were the two that were actually simple to access, when I pull my floor they are right there.

 

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You are entering a "Brave New World."  Please keep us posted on the installation, performance change if any and most critically, it's long-term effect on the engine reliability.

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I think you are good to go. I think the factory setting is right about where I would set it. The excess gets re routed to the tank. Having enough fuel and above the minimum pressure will add to reliability.

It will be interesting to see what the fuel pressure is at full throttle.

Bill 

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Brett, that's my fear. After speaking to the dealer that has done a few coaches and a bunch of Dodge Rams I felt better. They were kind enough to share their experiences with me, good and bad. They have only completed two ISL's several ISM's and a bunch of ISC and ISB coaches. None of theirs relocated the pump close to the tank on a DP. Apparently I'm fortunate to have space to relocate the separator and the pump down stream and have open access to the fuel tank. Fass recommend the placement of the pump as close to the tank as possible which on a Monaco works out since the next compartment forward is my power distribution. locating a ignition circuit should be simple, plus I have a bunch of open fuse spaces for adding circuits so I can make it look like it belongs.

Bill I'm shocked how many Rams have had this done and how many companies make kits to do it on those. Most include performance upgrades which I have no interest in. I just want it to stay together and go down the road.

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Almost ready for the big install. I have to source aluminum for the floor where the propane tank once sat, then its onto mounting the separator and pump, since the pump and filter will partially block my access to that area I have to take it one step at a time. I have fabricated up the mounting system for the pump and filter are all connected and mounted up on the tower I built, wiring is ran to the pump area and connected to a power source. Fuel pressure gauge is mounted in the dash, I just need to run the wire to the rear of the coach to the secondary filter housing where the sensor is mounted.

Work in progress.......I'm considering building a pull out drawer for where the propane tank once sat, I need to source slide rails for that, maybe buy a slide drawer from an RV salvage place and cut it down so it fits. The space is 26" X 88" Next to the fuel tank. Great place for tools, filters oil etc.

 

Also relocating my air chuck for airing up tires. It is on the roadside now, moving it over to the curb side, same compartment. Not sure who thought that was a good idea but I do not like playing in traffic.

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That would not be a good place to have a built in BBQ!  LOL...slide out trays are inexpensive, I had one made to size for a Colorado P/U bed with glides it was less than $500 installed.  Dealer will charge $1,500+!

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Yea, I'm finding that used ones cost as much as new ones when shipping is factored in :huh:. Trying to find just 60" drawer slides, I can build the drawer myself. cant seem to locate any on the web.

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Joe,

Colaw's has several trays(used) in stock' Do I remember that you or maybe it was Blake that was going to the Bass Pro Store in Springfield? Colaw's is just West of there about 35 or 40 miles. I will be there at the end of this week. I to am looking for the slide mechanism and can make the drawer myself.  

Herman

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Herman, thank you. I called Vision one they had a tray, wrong width but I can cut it down, the price was $390 plus $110 for shipping. Seemed high for a used tray. Still looking....

Carl, no idea why the posts are double, I was getting error messages today also but the posts still are posting. So far tonight it's ok.

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14 hours ago, hermanmullins said:

Joe,

Colaw's has several trays(used) in stock' Do I remember that you or maybe it was Blake that was going to the Bass Pro Store in Springfield? Colaw's is just West of there about 35 or 40 miles. I will be there at the end of this week. I to am looking for the slide mechanism and can make the drawer myself.  

Herman

I am in the same boat, I really just need the slides, I can take it from there, I figured if I got the tray also so be it, I will just alter it for what I need. I looked into ordering a new one but they do not make one in the width I need, and I do not want to buy a new one only to cut it up. Must be Blake headed that way.

I have to figure out what all of the hacked up wires are in that bay tonight, some one ran three wires around the propane tank and not its gone they are hanging below the floor level, one looks like a phone wire the other two are two conductor with wads of electrical tape on them. I've got to follow them back and front to see where they go. They are actually wrapped around the floor frame....some people should be required to take a test before they are allowed to purchase tools.

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Where I plug in cable, there is a plug for a phone.  Maybe your bundle is for CB?  Take it apart and see what does not work...:D

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Joe, a thought.  Did your coach come with satellite pre wired?  Could be your bundle is for bedroom TV for sat connection....home improvement by owner! :P 

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It has an auto search satellite dome on the roof, King Dome brand its painted the color of the coach. I do not use it, cable plug in or antenna and I'm good. Funny the box inside is marked that it will auto seek while driving, but the TV shuts off when you start the engine :lol:. Glad that wasn't a selling point.

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Joe, 

The in motion is so the kids may watch TV on the back TV.

When I redid theTv's my front unit would play even with the ignition on. Our grandson was with us and was watching TV and every time we would go under an overpass it would drop the signal but come right back on.

Herman 

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Herman, is there a relay somewhere that could be disconnected? They watched DVD movies while in route in the old coach, cant do it on this one.

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Joe. I gave you the answer to your wire bundle under Electric...I think!    Where ever you posted the oil in LPG tank.

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Let me ask for everyone's help on something:

Because many members use the "search" function to find answers to their questions, PLEASE, let's stick to the original topic

Having a good discussion of another topic than the original will not show up if someone is doing a search.

Starting a new topic IS THE RIGHT WAY TO DO IT.

THANKS.

Moderator

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Brett, question; the original design of the fuel system incorporated a check valve on the inlet of the primary filter so fuel would not empty back to tank.

Do you think I should incorporate one on inlet of the primary filter again?

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56 minutes ago, jleamont said:

Brett, question; the original design of the fuel system incorporated a check valve on the inlet of the primary filter so fuel would not empty back to tank.

Do you think I should incorporate one on inlet of the primary filter again?

Sorry, I do not know the answer.  Were I to get into any major change, I would sure involve BOTH a senior Cummins tech (i.e. hands on with your engine family) AND a Cummins engineer.

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Update; pump and filter mounted, first bay behind curb side steer tire. I fabricated a bracket system kind of like a tree to hang all of it on. I located all of this on the right side (curb side) just in case I needed to access it along side of the road, I will not be out in traffic this way.

Brett; I took your advice and made a few phone calls, the response I got was kind of scary. I was told an inline check valve is already supposed to be within 6 feet of the fuel tank from the factory, however mine is 38' from the tank on the inlet side of the primary filter. My primary filter is also supposed to be close to the fuel tank, YUP, its not! Someone didn't follow the engine manufactures guide when the coach was built.

The check valve from the factory is a 2 PSI crack pressure, I ordered an inline 2 psi crack pressure check valve that will thread directly onto the fitting at the fuel tank, this hurdle is solved.

Mystery wire update; that went to a red light on the dash that wasn't connected, the other end was one of the wires that was bare and hanging near the existing fuel pump on the engine, looks like someone started to wire in a low fuel pressure warning lamp circuit and gave up (photo of the terrible wire installation in the gallery tab, I cleaned all of that up and placed it into a loom). I recycled the light and its now a Water in Fuel light for the primary filter, so I now have two water in fuel lights, busy night last night. Oh, I also added an second sewer hose storage tube in that bay, what you cant see is both are tilted downward and there is a hole in the floor directly below where any remaining water in either hose will drain out of the coach, not into my storage bay.

So what's left you are thinking;

  1. Mount the fuel pressure gauge manifold with sending unit after the secondary filter housing in the engine bay.
  2. Pull fuel pressure gauge wires to the dash gauge, gauge installed, wiring harness in electrical bay in front of steer tire.
  3. Connect all of the hoses I had pre made.
  4. Remount the chassis air supply air chuck to the filter tree.

 

Gauge installation

 

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Joe.  Great job! :D Now, if you should get any more junk in fuel system...no complaining! :lol: Just kidding!  Did you put in new fuel lines?

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Thanks Carl! I replaced all of the fuel lines in July 2014, now to finish up this job some of them will be discarded (capped off and tied out of the way) while the main one that runs from the engine bay to the fuel tank will be just added to so it can reach the new pump on the curb side. I'm sure there is some junk in the tank, now I will be able to see it in the filter upfront since it is a clear bowl. With the gauge on the dash I can also monitor the filter condition electronically, as the pressure drops time to manually look at the one up front, if its not full the one in the back is the culprit and needs to be changed.

 

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