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Old 05-05-2016, 07:37 AM   #1
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Repeating CAPS Failures - Need Help

We have just recently had to have the CAPS Fuel Injector Pump replaced for the 3rd time in a little over 3 years. The first time the accumulator was replaced - the second time the whole pump was replace along with the lift pump - this third time the whole pump, lift pump, and suppressor were replaced. We have contacted Holiday Rambler, Cummins Distributors, and Cummins Corporate to request help in identifying a method to locate the root cause. So far fuel test for contaminants and then tank clean if needed is the only identified potential root cause.
The mh is a 2002 Endeavor diesel with 47,000 miles and was purchased in '08 from the first owner with 21,000 miles at that time. We had about 15,000 miles before 1st failure and have about 11,000 miles from 1st failure to the current 3rd one. We take care of the mh and have never mistreated it and thought we did acceptable fueling at truck stops and winterizing here in Colorado winters.
Any suggestion on how to proceed in finding root cause would be appreciated or any comments about any obvious things we are not doing correct would be appreciated.
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Old 05-05-2016, 08:07 AM   #2
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Have a fuel pressure gauge installed that you can monitor.

Find out what normal pressure is and have the system checked if it is out of range.

I understand that low fuel flow causes pump failure due to exesive heat.

Also, don't let anyone pour fuel into the filters when changing them. The lift pump is suposed to fill the filters and push the air out. If it can't, there's a problem.
A pressure gauge will indicate low flow, due to lack of back pressure.

I found this info on a Dodge diesel forum.

The engine will run with a bad lift pump, but not have enough flow to cool the injector pump.
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Old 05-05-2016, 09:55 AM   #3
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Twinboat gives good input. The CAPS takes very pulling/sucking fuel in from the tank, after the Lift Pump does the start up lifting. Any restriction of fuel flow can starve the CAPS, and that is not good.

My OEM Lift Pump was still working fine, ISL370 built July 2003, did not develop any leaks. However, I elected to proactively bypass the Lift Pump and installed a FASS Fuel Pump (pump only, no the duel filters). Alan of Brazel's, did a great install, leaving the OEM Lift Pump in place, and the plumbing available to allow it to be reengaged with a little adjustments, if ever needed.

I did this because I did not want to replace the Lift Pump with another Lift Pump. I also wanted to keep positive fuel pressure feeding the CAPS at all time, not just start up.

And, I always add extra lubricity at each fill up. I use Optilube in each tank. This also provides a bit more insurance to the CAPS.

As mentioned, the CAPS is both cooled and lubricated by fuel. So I try to give it all the help I can!

ColoradoHRE - Your second post, so welcome to the gang! And please close the loop back and let us know if they do find anything out that may have contributed to the early demise of the CAPS. Those are big ticket repairs, and not fun!

Best, be safe, have fun,
Smitty
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Old 05-05-2016, 11:16 AM   #4
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Thank you twinboat and smitty77 for the response to the CAPS failures - obviously badly needed. (costly - yes about $15,000 for just the repair bills and then the other expenses are not trivial while it is being repaired with us on a trip each time the failures occurred.)
I want to pursue the mods so we can observe what is going on with the fuel feed to the CAPS pump because the results of low pressure causes results that are identical to what we are experiencing. I need to understand the standard operating process better that goes on between the lift and CAPS pump as a starting point so thanks smitty77 for your description of your mods. I will follow up with the Colorado Rocky Mountain Cummins service manager to make sure I understand the process clearly and try to find out why he has not suggested that cause but only homed in on fuel contamination and the fuel test and tank clean if the test shows significant contamination.
Also - Our first two failure's symptoms were warning light on and off with jerky operation and each fix cured the symptoms. This last failure caused the warning light to stay on continually and we had significant increasing loss of power to the point that we had the coach towed from Kingsville, Texas to Corpus Christi where the repair was done but there was no jerking just significant loss of power. After the CAPS, lift pump, and electronic suppressor replacement the operation seemed normal for our 1,300 mile trip back to Colorado. The Corpus Christi Freightliner service policy for a CAPS repair is to always change the lift pump and suppressor at the same time. I was going to have the CAPS failure analyzed but CCF understood that but had already sent the defective pump off and because it is not serialized - it got mixed with other pumps and they could not guarantee they could get the correct pump back for analysis. The failure diagnostic did localize the failure to one of the plungers not operating any longer but that was the extent of the diagnostic information.
Thanks again for the tutorial information on the fuel delivery system and I will give feedback as we go through the cause identification and fixing process. We are obviously nervous about doing any trips with our coach at this time so we hope that a high probability cause can be found.
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Old 05-05-2016, 12:51 PM   #5
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I downloaded the Cummins Bulletin 3666321, which has a decent explanation of how the engine and various components work.

Here is what it says about the Lift Pump
The ECM controls the electric lift pump located
between the fuel tank and injection pump.
Whenever the keyswitch is turned to the ON
position, the lift pump will be energized for 30
seconds to make sure that the low pressure
fuel lines are fully primed. The electric lift
pump does
not start again unless the

keyswitch is cycled.

I'm wondering if there may be something in the tank that gets sucking into the fuel pickup tube and starves the fuel pump for fuel. Something is definitely wrong.

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Old 05-05-2016, 04:59 PM   #6
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It's kinda obvious to myself and others that you are dealing with a fuel starvation issue,
if it were me I would most likely pull the fuel tank install a new pickup and make sure visually that the tank and it's fittings are clean tight and installed correctly with my own 2 eyes.

Then I think I would pull new fuel lines from the tank to the filters and pump.

I'm thinking you may have a fuel line either rubber that has a collapsed inside or maybe a tie down clamp that is to tight and causing fuel starvation.

I would think seriously about buying a silverleaf vmspc to monitor the fuel pressure

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Old 05-05-2016, 05:22 PM   #7
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I have a Silverleaf VMSpc,

Is there a gauge that allows you to monitor fuel pressure, what is it called?
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Old 05-05-2016, 05:23 PM   #8
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ColoradoHRE I'm assuming you are having both your fuel filters changed regularly.
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Old 05-05-2016, 06:36 PM   #9
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I somehow remember hearing about another CAPS multi replacement that was finally tracked back to an inline fuel filter that was not known to the owner. He had changed the normal filters, but was unaware of the inline filter (Found somewhere running along the frame.), and it was the root cause of his problem. The Lift Pump did the initial start, as it should have, but then the CAPS worked much harder then it should with what he called occasional stutters, before the second CAPS failure. (Makes sense, as the inline fuel filter was that much older, with that much more crud built up.) The first time, he detected no performance problems, until the failure hit.

You might check in with the Owner Group of your rig, and ask around if they know of any inline fuel filters... Sure worth checking, and costs nothing but a little research.

And again, best to you, and welcome,
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Old 05-07-2016, 10:45 AM   #10
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Thanks so much for the additional postings - helps getting experiences!

About fuel filters: We have changed regularly but have used judgement that hopefully has not caused the failures.
My understanding is that Cummins states fuel filters should be changed at oil change/servicing (15,000 miles, 500 hours, 6 months). We have done that at 3,000 to 4,000 miles and the time is usually about 1&1/2 years. Sometimes the 6 months would have had essentially no mileage and we did not do that. HR owner manual says do change at 12 months regardless of accumulated mileage for that interval.
Our future change interval for the fuel filters is going to be 6 months max regardless of oil change interval to be conservative.

About pressure gauge: Plan on doing that so we have a real time monitor on the important parameter that each of you have noted. The only fuel related gauge in the coach at this time is the fuel tank fill level.

Also plan on doing lubricity additive to help with that aspect. Still will use temperature gelling inhibitor but will need to research and check out if that puts additional risk on the fuel pump. Everything I have heard on that is that should not hurt the fuel pump but I need to do more checking. Any comments on this?

Plan on physically checking the in-line filter that Smitty77 pointed out - the documentation does not show any in-line filter but I will check that out. Not sure how to check the fuel line except to first visually trace it as a starting point. Will locate the fuel vent and see if it looks ok - any problem with the vent should have shown up as other bad symptoms so it is probably ok.

Fuel test is scheduled for May 19 with engine and generator servicing. Follow up will depend on results. Will follow up with posting of results and thank each of you for spreading some hope that this thing can be fixed.

Regards
Another question: Do you know where the air vent is located for the lift pump to prime the fuel line - in the caps injector pump or the second filter?
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Old 05-07-2016, 11:46 AM   #11
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There is no 'air vent' for the fuel system EXCEPT for the tank. Any air goes through the injection pump and is expelled either through the injectors or the fuel return line. Far as a fuel pressure gauge, the only time you would normally see pressure is the first thirty seconds when you turn the key on. After that the injection pump pulls the fuel on its own.
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Old 05-08-2016, 08:17 AM   #12
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Thanks MnTom for the posting - As you can see I am still trying to accurately model the fuel input portion of the system. The fuel return line is the purging component that I was not taking into account. Sounds like the purging of air is a straight forward priming loop that the lift pump does on initial 30 seconds or a couple of 30 seconds as mentioned by others if they have to use the key turn a couple of times.
My understanding or misunderstanding from other descriptions is that the lift pump can be defective and cause fuel starvation but I do not understand how that happens if the lift pump is only a priming pump. Is it because the fuel has to flow through the lift pump during normal running and may be constricted there or some other mechanism that I still do not understand?

It looks like any contriction from the fuel pickup to the input of the injector pump can cause fuel starvation as well as the injector pump itself not creating enough vacuum.

As an aside, I am trying to model the pressure/vacuum levels from the tank to the injector pump during prime and running condition to gain a better understandding of how all of that works. Smitty77's mod to use a pressure lift pump full time has been the stimulus for me to try to understand that because he is actually putting a pressure feed onto what you and he have pointed out is a designed vacuum/pull feed during normal run time. Does that looks like it eliminates a number of potential constrictions at the lift pump and vacuum source at the injector pump?

Any comments would be appreciated -
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Old 05-08-2016, 07:15 PM   #13
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I am not real familiar with the CAPS pump, but this should give you lots of good info: http://www.ganino.com/games/Prednje%...%20gorivom.pdf
It explains some of the things that happen with the pump.
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Old 05-09-2016, 08:01 AM   #14
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Quote:
Originally Posted by MnTom View Post
I am not real familiar with the CAPS pump, but this should give you lots of good info: http://www.ganino.com/games/Prednje%...%20gorivom.pdf
It explains some of the things that happen with the pump.
Thank you MnTom for the link to the Fuel System documentation. I had been looking for that kind of info and had not found it so far - so great help to me in learning about the system that is giving us so much difficulty. So far in looking at the info, I am realizing that the pump is even more complex than I had thought it was from some of the descriptions that the various tech's that have worked on our coach had given me. Great resource - thanks again for the help!
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