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Old 05-26-2023, 05:06 PM   #29
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The stock CAPS-1 system electric lift pump provides positive fuel pressure to CAPS gear driven pump. This positive pressure is usually enough to start the motor; and then the CAPS gear driven pump takes over and sucks fuel from your tank.

In a closed system, the gear driving pump provides barely enough suction to draw fuel from a tank located some 30+ feet away. However, if there is any air leaking by the electric lift pump gasket (a common problem in CAPS-1 systems) you will experience a variety of symptoms. These include engine no-start conditions; or you engine may stall out 30 seconds after the engine starts; or you may experience hesitation while climbing a steep highway grade. Of which, all of these symptoms point to air being sucked into the fuel line; and it has nothing to do with “bad fuel.”

Further, if you are convinced you solved your engine fuel starvation problem, buy just changing your fuel filters, I’m hear to say, you are not alone, but you are fooling yourself!

What is really happening is this: As miles accumulate, the fuel filter traps more and more debris; and the filter starts to de-rate fuel flow. And while this is NOT a problem for an airtight fuel line, it will cause problems in a weak or compromised fuel delivery systems... operating on the borderline.

CAPS-1 owners usually can fix an air leak problem by just tightening their 3 lift pump bolts. And I recommend you do this if you are one of those owners who thinks they got bad fuel -- and you think you fixed your engine no-start of hesitation problem by just replacing fuel filters -- because there is more going on!

The better solution to a Cummins electric lift pump, used on CAPS-1 systems is to provide constant "POSITIVE FUEL PRESSURE" by installing an AirDog or FASS electric fuel pump.

Note: I prefer FASS because I like that it recycles a lot filtered fuel back to the tank, but AirDog may be an easier installation for some model RVs.

Starving your CAPS system of fuel time-and-time again could untimely cost you a full CAPS system replacement at a cost over $5000. And if you blow your ECM in the process you could be looking at a $8,000+ repair and weeks of downtime.

So, IMO, you should take the time to find and tighten your CAPS-1 lift pump bolts. It’s free! You just need access to the top of your engine, on the passenger side or you can chance it and keep driving on. Plus if you put 1/4 turn on each of those bolts then you know you found where you are leaking air. (Don't overtighten!)

Note: If you have CAPS-2 (2005-2007) ISC/ISL engine then you have a different electric lift pump vs. CAPS-1. This CAPS-2 lift pump is not subject to air leaks, so much, but you do need to be more concerned about “FLAPPERS” appearing inside your deteriorating fuel lines.

These “FLAPPERS” create air bubbles and foam in the fuel delivery system that causes engines to stall-out when driving, because your electrical sensors detect low fuel pressure and your ECM will shut your engine down, leaving you to wonder what the heck is going on? (And big bucks paying a tech who does not have any engine codes to go by.)

These Flappers don’t seem to occur in pre-2005 RVs because these coaches came with higher quality fuel lines. And by 2009+ Winnebago started again to use better fuel lines. So only CAPS-2 systems, between 2005—2008, seem to have this problem, which can also be solved by adding a FASS or AirDog that remove air from the fuel. (Albeit, installation is a little different on a CAPS-2 vs CAPS-1.)
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Old 05-27-2023, 11:31 AM   #30
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Caps actually ended in 2005, but as in all things class A the manufacturers used in stock motors for up to 3 years after they were out of production. Maybe longer for reasons of hoarding a few of the better motors.
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Old 05-28-2023, 10:26 AM   #31
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Quote:
Originally Posted by shootist View Post
Caps actually ended in 2005, but as in all things class A the manufacturers used in stock motors for up to 3 years after they were out of production. Maybe longer for reasons of hoarding a few of the better motors.
Important to realize , that there was a transition injection system ; CAPS II (2)
and pictures of the CAPS II , injection pump ; show that it has no fuel distribution to individual injectors like the CAPS pump ; so I assume that it's the earliest version of HPCR ( High Pressure Common Rail ) although tracking down the years of use or a fuel system diagram is proving problematic .

EDIT : Note to self ; read all the posts in the thread before posting ; I see 2004Horizon has posted info about the CAPS II system years of use.
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Old 05-28-2023, 12:11 PM   #32
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Usually the Notes to Myself get lost in transition and it seems to be getting worse as time goes by.

I've been in my shop working on something and walk 15 ft to the bench to get something and forget what I was after.
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Old 05-28-2023, 05:31 PM   #33
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Here’s a link that seems to be contrary to my own statement, says 2003 to 2007 . Who knows.

https://www.tamerx.com/oem-4076442rx...yABEgLCPfD_BwE
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Old 05-28-2023, 05:32 PM   #34
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Originally Posted by jacwjames View Post
Usually the Notes to Myself get lost in transition and it seems to be getting worse as time goes by.

I've been in my shop working on something and walk 15 ft to the bench to get something and forget what I was after.

Your not alone ... I can get out of my chair , and I've forgotten why I'm getting up.

BTW; It's not necessarily Alzheimer's if you can't find your car keys ... now if you have car keys and don't know what their for .. that's a different story.
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Old 05-28-2023, 07:55 PM   #35
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The point is not CAPS1 Vs CAPS2, but what type of lift pump they use. I.e., if you have a CAPS1 lift pump then you MIGHT be able solve your compromised fuel pressure/suction problem buy tightening the 3 lift pump bolts, which is not an option on CAPS2 lift pumps since they work on a different design and principle.

Point #2: When it comes to upgrading to a FASS or AirDog these installations are slightly different depending on the type of CAPS1 or CAPS2 or HPCR system you have.

Point#3: Changing fuel filters prematurely is not a solution to a fuel starvation problem. It's a panacea.

Point #4: If my CAPS1-Accumulator was "gummed-up" with algae, I don't know if you can fix it, but I would start by running a high concentration of BiBour through your system... and let it sit a month to see if killing the algae works before you replace your accumulator; that is if you can find a mechanic who knows how to do that as this is a lost art.

Note: In my Itasca Horizon with a basement AC, it is really hard to access the CAPS1 injection pump from under the engine. However, if you pull your basement AC out then you will have easy access to the entire passenger side of your ISC/ISL and you will say yourself hour of headaches! Plus, this would be a good time to overhaul your basement AC if you have done so already!
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Old 05-30-2023, 03:36 PM   #36
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Sorry for the late response. You guys have me really concerned. You think the filters weren't the problem? I doubt my lift pump is leaking because I bought a brand new one from cummins last year. I definitely would have installed a FASS pump or Airdog had I done my homework before buying the $500 dollar plus lift pump from Cummins with a (made in china) stamp on the box. What do you guys suggest I do now? It's running fine it never turned off on me before.

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Old 05-30-2023, 07:00 PM   #37
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I would buy spare filters and have a wrench to change them


Just keep an eye on it. If the engine doesn't throw a code you are probably fine.
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Old 05-30-2023, 08:15 PM   #38
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I also bring some diesel to prefill mine.
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Old 05-30-2023, 11:33 PM   #39
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CampoutWill: My point is that when you start changing fuel filters prematurely to fix a fuel delivery problem, and it works, this is very often a panacea and not a solution.

If this condition persists you will only discovery it when it's cold outside and/or when you climb a step grade in an aggressive manner... and your engine hesitates, which goes away when you back of the gas pedal. ...At which point, you stop thinking about it and thank God it doesn't hesitate again!

The good news is that you can easily check the torque on your three lift pump bolts, by accessing the top of the engine on the passenger side. And if you find that you can put 1/8 or more turns on any or all the bolts, then you can rest even easier, knowing you probably cured a POTENTIAL air leak down the road.

IMO, CAPS-1 owners should check the torque on their lift pump every 15,000 miles. (which works out to be 2-5 years for the average RV owner).

In conclusion, for decades I have noticed that owners want to believe they must have picked up some bad fuel when their engine will not start and they want to believe new fuel filters cure the problem. However, IMO, and experience, 99% of the time it's not what is going on with CAPS-1 fuel deliver systems that use a Cummins lift pump.

Further, IMO, if any mechanic tells you to R&R a lift pump in a CAPS-1 system, then I too would rather spend that money on a FASS or AirDog -- and bypass your old lift pump.

On a different subject, your CAPS gear driven pump is a "weak link" in a CAPS-1 fuel delivery system. Of course, you can't get rid of your gear pump and you don't want to. What you want to do is deliver positive fuel pressure to the gear driven pump and this is what the FASS and/or Air Dog does.
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Old 06-04-2023, 11:24 AM   #40
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Filters are never the problem. The problem is what the filters are catching from the tank. They are just doing their job and telling you you have a problem.
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