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Old 05-25-2022, 07:06 AM   #1
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Caps pump pressure gauge

Is there a way I can install a pressure gauge in the dash that shows the cap pump pressure , so I can keep an eye on it, before it fails in the middle of no-where?
2000 Monaco exex. ISC engine
60,000 miles
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Old 05-25-2022, 08:05 AM   #2
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Because the CAPS main injector pump , has a mechanical low pressure pump in one section and the high pressure injection pump in another ; finding a spot to tap in for a fuel pressure gauge would be an issue .
The CAPS system uses it's electric lift pump as a primer pump and only cycles it for approx 30 sec. at key on; then the mechanical section on the CAPS pump takes over.

Many members with CAPS have installed a FASS electric pump system that runs full time with the engine and report good results.
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Old 05-25-2022, 08:30 AM   #3
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I was hoping there was a tap on the pump for this gauge/transducer.
I haven't looked for the pump yet as I don't know where its located
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Old 05-25-2022, 08:51 AM   #4
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Here's a diagram of component locations and a photo of a CAPS injector pump .

I have a CAPS system overhaul manual that's too big to post in the forums ; I'll look through for a mechanical pump pressure test port .
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Old 05-25-2022, 09:16 AM   #5
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No info on a pressure test port on the gear ( mechanical ) section of the CAPS injector pump , only some specs .
The gear pump is regulated to 140 PSI at governed engine RPM .

I will have another look ; but the pdf jumps back and forth between CAPS and the newer HPCR fuel system so it takes some reading to get correct info .
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Old 05-25-2022, 09:22 AM   #6
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Yup, the lift pump only runs for ~30 seconds so any gauge in front of the CAPS pump will only show pressure for that time, after the CAPS pump is pulling fuel.



X2 on the FASS install. I did one last year on my coach and installed a pressure gauge on the dash. Turn the key and I see ~16psi on the gauge (the FASS pump is regulated to that psi), start the engine and see ~16 psi on the gauge. If I am on a hard pull the gauge may drop to ~13psi but quickly recovers when I let off the throttle.



Suggest doing some research on the your options, I did and ultimately decided installing a FASS pump was the way to go.
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Old 05-25-2022, 11:52 AM   #7
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Quote:
Originally Posted by jacwjames View Post
Yup, the lift pump only runs for ~30 seconds so any gauge in front of the CAPS pump will only show pressure for that time, after the CAPS pump is pulling fuel.



X2 on the FASS install. I did one last year on my coach and installed a pressure gauge on the dash. Turn the key and I see ~16psi on the gauge (the FASS pump is regulated to that psi), start the engine and see ~16 psi on the gauge. If I am on a hard pull the gauge may drop to ~13psi but quickly recovers when I let off the throttle.



Suggest doing some research on the your options, I did and ultimately decided installing a FASS pump was the way to go.

A guy that owns a diesel repair business said to put a gauge on it and keep and eye on the gauge because when it fails it takes out the injector pump.
So I don't know if he meant to monitor on the suction side or discharge side of the pump
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Old 05-25-2022, 12:43 PM   #8
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Quote:
Originally Posted by straycatboat View Post
A guy that owns a diesel repair business said to put a gauge on it and keep and eye on the gauge because when it fails it takes out the injector pump.
So I don't know if he meant to monitor on the suction side or discharge side of the pump

He may have assumed that the lift pump runs constantly…. It doesn’t. Just the first 30-45 seconds.
I believe some cummins powered Dodge trucks have a lift pump that runs constantly and a gauge between the lift and main pump is a good idea.
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Old 05-25-2022, 01:50 PM   #9
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Quote:
Originally Posted by Skip426 View Post
Here's a diagram of component locations and a photo of a CAPS injector pump .

I have a CAPS system overhaul manual that's too big to post in the forums ; I'll look through for a mechanical pump pressure test port .

So school me on this.
It looks like #9 is a lift pump so I guess it draws fuel from the tank and sends it to the CAPs pump, which is the high pressure injection pump???
.... so if the lift pump fails it damages the Caps injection pump?
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Old 05-25-2022, 03:27 PM   #10
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In the past the problem has been the lift pump starting to leak when pumping, but after 30 seconds the injector pump pulls fuel from the tank through the lift pump and at the same time starts sucking air (due to the leak). The air is the problem and is bad for the injector pump and will ultimately cause failure.


Back in ~2006 Cummins put out a Technical Service Bulletin TSB, see attached, on this and instructed shops to inspect and if they found a leak change the gasket. Cummins quit doing that and left it up to the owners. A new OEM lift pump is ~$500. A FASS install is less then $1000 for the FASS pump, hoses, and pressure gauge.



When my lift pump started to leak I thought about it and decided to go the FASS route.
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File Type: pdf Cummins ISL Lift Pumps service bulletin.pdf (214.6 KB, 7 views)
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Old 05-25-2022, 06:02 PM   #11
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Quote:
Originally Posted by straycatboat View Post
So school me on this.
It looks like #9 is a lift pump so I guess it draws fuel from the tank and sends it to the CAPs pump, which is the high pressure injection pump???
.... so if the lift pump fails it damages the Caps injection pump?

Ok , #20 in the diagram is the CAPS pump .
On the CAPS system the electric fuel pump is referred to as a " primer pump " because it only runs for 30 secs. from key on.
The multi sectioned CAPS injector pump has a mechanical fuel ( lift ) section to draw fuel from the tank and delivers fuel at up to 160 psi , to the high pressure section of the pump ; where it is boosted to a pressure that will force open the injectors; up to 24,000 psi.
On the ISB Cummins In particular those , early years, with a VP-44 injector pump , the " lift pump " runs continually and failure, of the lift pump ; WILL cause the VP-44 to fail due to fuel starvation .
To the best of my knowledge , Cummins has used 4 different fuel injection systems on the 5.9 , and three on the 8.3 , Prior to the introduction of HPCR , only one injection pump is common to both engine sizes , the mechanical P-7100 .
Each Cummins fuel system has it's own particular issues , so it's VERY important to know exactly what series of engine; and injector pump; your dealing with .
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Old 05-25-2022, 09:42 PM   #12
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Caps is the low pressure pump. The high pressure side is the accumulator. That's the head on top with those two solenoids. The accumulator pressure is pre set at factory and shouldn't be messed with. On the end of the accumulator head is the fuel pressure sensor. If you want to monitor your fuel pressure I suggest you get a analyzer that you can monitor through the interface under the dash.
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Old 05-25-2022, 09:57 PM   #13
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Personally, I think Cummins made a mistake with the ISC. It's good for dump trucks and some commercial/farm equipment where the Caps pump is closer to the fuel tank. On a 40ft motorhome you are asking the Caps pump to suck fuel for over 40ft. Just doesn't seem right. They should have designed a similar Fass pump to begin with. Your filter housings should have a port on the top you can screw a sender into (with a metric adapter) and run wire to the dash and install a gauge, or install the gauge at the filter housing. The lift pump will run for 30 seconds then the Caps pump should take over. Even though the lift pump turns off, you should be able to read the pressure that the Caps pump is pulling I would think. I installed an Airdog only pump and put a sending unit on one of my filter housings. Glo Shift gauges sells a 40ft wiring harness for their fuel gauges, so I bought that and ran the wire up to my dash and cut a hole in the dash and installed their gauge. Like Jacwjames said, it pulls 15 psi constantly. Under heavy throttle it may drop a pound.
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Old 05-26-2022, 07:37 AM   #14
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Quote:
Originally Posted by Skip426 View Post
Ok , #20 in the diagram is the CAPS pump .
On the CAPS system the electric fuel pump is referred to as a " primer pump " because it only runs for 30 secs. from key on.
The multi sectioned CAPS injector pump has a mechanical fuel ( lift ) section to draw fuel from the tank and delivers fuel at up to 160 psi , to the high pressure section of the pump ; where it is boosted to a pressure that will force open the injectors; up to 24,000 psi.
On the ISB Cummins In particular those , early years, with a VP-44 injector pump , the " lift pump " runs continually and failure, of the lift pump ; WILL cause the VP-44 to fail due to fuel starvation .
To the best of my knowledge , Cummins has used 4 different fuel injection systems on the 5.9 , and three on the 8.3 , Prior to the introduction of HPCR , only one injection pump is common to both engine sizes , the mechanical P-7100 .
Each Cummins fuel system has it's own particular issues , so it's VERY important to know exactly what series of engine; and injector pump; your dealing with .

How would I know what fuel injection system I have.

(2000 Monaco Exec.)

I have all the books and build sheets but all it says is 350 ISC Cummins engine, no reference to the fuel injection system.
See pic below
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