1) The CAPS pump costs ~$3,500 for the part to replace and $3500 - $5000 to install due to the difficulty of the R&R process. My Freightliner chassis is the worst when it comes to being easy to work on the CAPS pump. Your Spartan Chassis may be better. Also, I have a basement AC on the passenger side of my coach so I don't have side engine access like some RVs do after they lift up the compartment grill. (I do not know what you have?)
2) When you CAPS pump goes it can throw a huge electrical "spike" back to the ECM; that overcomes the ECM Suppressor Diode (aka protection diode) and many mechanics tell me that 8x out of 10 they also replace the ECM when they replace a CAPS pump.
So while we both own one of the best, every built Cummins engines (ISC), you need to know your CAPS injection pump, which was not designed to run on ULSD fuels, and was built to very tight tolerances, will prematurely fail if it does not receive enough lubrication and cooling from the fuel. This is one reason most of us use an additive. You like PS-Diesel. I like Howe's. It's all good for a CAPS system.
==> You might want to read more about fuel in this thread: "Fresh Diesel vs Bio Diesel" http://www.irv2.com/forums/f59/fresh...el-458351.html
Note: Everything I have written about has been a journey, so feel free to read the fist post and then go to the last posts where I try to provide a summary.
Back to the subject at hand:
In 2015, my CAPS and ECM failed and Cummins charged me $9,500 for the complete job. (And that did not include the towing bill.)
...And so, protecting my CAPS pump from another failure maybe the the #1 reason I went to a FASS fuel pump. However, after I installed the FASS "TS" Pump I really like the extra 2 fuel filters; and the "fuel polishing" that I think eliminated my algae concerns. Not to mention a better sounding engine at idle and no more "bucking" up a hill.
Whatever is going on, my engine now runs smoother; and yes... positive 15-18PSI of fuel pressure is always better then -5PSI of vacuum pressure.
And now that I have a FASS Fuel Pump I know my CAPS low pressure gear pump will never be starved of fuel in the future! I also have every reason to believe my CAPS injection pump will last a lifetime now that's it's receiving positive fuel pressure and I'm not worried about bio-fuels like I use to be. In fact, all studies show, bio-fuels have MORE LUBRICITY than #2 USLD fuel. So if anything, I would like you to know you don't have to be concerned about bio-fuel wrecking your CAPS pump. (If you read that thread about "Fresh Diesel vs Bio-Diesel" then you know this now.)
Would I buy an older RV with a CAPS injection pump again? YOU BET! I would not only get a better value and lower price; I now know a CAPS pump will run forever if you install a FASS or AirDog Lift pump... and I would do that immediately if I was a new owner.
Note: If you don't drive your RV very much, and/or this is your last year of ownership, then you might not want to upgrade to a FASS pump. Just know this: In my opinion all CAPS pumps are running on borrowed time if they don't have one of these little jewels!
3) Only the older mechanics, who use to repair CAPS injection pumps, know how to repair these things. (Unless you are in farm country where a lot of older ISC-CAPS engine are still in service.)
For example: The accumulator (that rectangular looking aluminium block that sits on top of your CAPS pump) might get replaced if you had an algae problem. (My accumulator was replaced by the previous owner back in 2009 with only 40,000 miles on it, but back then he was fighting an algae problem.)
And then there is the STATOR that controls the fuel metering to the fuel distributor might be another part you can replace. (And still can. But first I would say good luck finding a mechanic who can properly diagnose a CAPS problem.) Note: There is an Engine code for the Stator and you need to check for this.
It's a $150 part and not hard to replace.
Here's a thread about my CAPS fault codes, but you need to know these were the codes after my CAPS pump blew-up. Still you probably have a few "low pressure" codes logged. Just remember to ask your mechanic to look at the HISTORY so you can see how many time your EMC logged "low pressure" as a fault.
Note: What about your engine light. Did it ever come on? Mine did a few times, but it will not always come on. Or your ECM will rest it and you will never see the engine light flash on the dash. However, your ECM will still log this time. These are "Soft Codes" and are worth looking at.
Note: And don't worry about your 10-micron fuel screen inside the CAPS pump. This will only get clogged if you have serious algae concerns.
...I remember at one point I was thinking a clogged CAPS screen filter might be my problem, and when I talked to 10+ mechanics, including those on Cummins Quick Serve... who never knew there was a 10-micron fuel screen in the CAPS pump... I thought I might have have just found my problem.. but no cigar! And after I examined my screen (in my broken fuel CAPS pump) it was clean.
3) Yes, the ECM will log several engine codes to help with the diagnosis, but because very few mechanics have ever taken apart a CAPS pump, more often or not they will just try to sell you on the replacement of one.
Think of it like this: At one time your car mechanic knew how to overhaul an Alternator; but now all he knows how to do is replace the Alternator with a re-manufactured unit.
Same goes for CAPS. In fact, I had so little confidence in the Cummins-Colburg, OR team that I felt forced to buy a complete CAPS pump, because I did not trust their ability to properly fix my failed CAPS pump. So don't think your Cummins Shop is more qualified to repair a CAPS Injection System over Joe's Garage. In fact, I would argue just the opposite.
To repair or replace a CAPS pump you two things: A) You need to find a mechanic 50-70 year of age who use to repair CAPS pumps; and B) You need to find a shop with a younger mechanic who can get inside your engine bay to do the R&R.
The problem most people face is that the right shop is the one you towed your RV to.
4) CAPS pumps are failing (in part) due to ULSD fuels they were not designed to run on, but the real reason for CAPS premature failure has more so due to fuel starvation... in my opinion.
I.e., every time your engine stalls out you are loosing negative fuel pressure (vacuum in the fuel line)... to the point there is not enough fuel for the low pressure gear pump to work.
This is also true when you engine bucks when climbing a hill or under acceleration. And not enough fuel means not enough lubrication and cooling. So these CAPS pumps are failing due to heat... and constant low fuel (vacuum) pressure... that is caused by leaking air getting sucked in where your lift pump gasket mates with the lift pump fuel manifold. And this is why many people find they can just tighten the 3-lift pump bolts and all is well again!
5) What else drops negative (vacuum) fuel pressure below the minimum -5PSI?
* Fuel levels in the tank below 50%. In the Dodge-Cummins world this is known as the "1/2 Tank Problem."
* Loose Lift Pump bolts
* Poor Tank Venting caused by bad fuel caps or even sand-dabbers building nests on top of your fuel tank vent.(although I don't have that one confirmed... other members have claimed this is possible.)
* Rotting out fuel lines??? This is something to watch for, but all I have heard is that you will see black specs in your fuel filter if you cut it open.
Here's the rub: A fuel line under vacuum pressure will lose pressure if the fuel line starts to suck air in through it's pours. This will cause your CAPS inlet fuel pressure to drop blow -5PSI and you will see all the symptoms you described. And fuel lines are the last on the list of things to replace when you can't find a vacuum fuel problem in an older RV.
Other solution: You can install a FASS Fuel Pump. One smart person (I think it was TR4) said: "Any amount of positive fuel pressure you can deliver to your CAPS pump is better than negative (vacuum) fuel pressure."
6) Cummins specs -5PSI as the minimum pressure the CAPS pump needs to operate properly. So you can bet, when you engine will not start or just quits, your fuel pressure will be less than this.. and your CAPS fuel pump is dying a slow death due to lack of lubrication and cooling.
Note: -5PSI is a common reading for vacuum pumps. So don't let that number through you if you are use to seeing +15-+18 PSI on a fuel pressure gauge.
IMPORTANT: You can measure your fuel pressure very easily in your engine bay, and I recommend every one do this: All you need to look at is the top of your fuel filter mount. And if you have a 10mm port on top of your filter mount then you can add the following parts to measure your Vacuum Pressure.
Note: This 10mm allen-plug would be on top of your secondary filter if you have 2 fuel filters in your engine. Cost (<$30).
Here's the parts you can order on amazon:
M10 x 1.0 Male to 1/8-27 NPT Female ($5): https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Oil Filled Vacuum Pressure Gauge - 1/8" NPT ($11):
Note: Some people might prefer a gauge you look at from "on top" vs. "on the side." These are available too. Plus most gauges have 1/4" NPT threads. I went with 1/8" NPT and a smaller Fuel Pressure Gauge. You might do something different, but given how easy it is, and how low cost it is to add a fuel pressure gauge on top of your fuel filter mount, I think everyone should do this... or install a remote electric fuel gauge if you want to go the "whole 9-yards!"
Here's the Scan tool I have used. (Thanks to another IRV2 member recommendation.)
Scan Tool ($119): https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
So my recommendation for you to diagnose your fuel delivery concerns in the future is to buy these items. After you tighten those 3-lift pump bolts!