CAPS, FASS and AirDog

[JDaveB]

Frank, do you believe the claims that these systems also remove entrained air from the diesel fuel? I think that is a benefit I can’t easily replicate with a pure fuel pump

Dave

[Fffrank]

Originally Posted by Mile Marker 42

When I originally read your post, I got under my coach (which runs fine) and could see the bottom of the pump slightly damp. For me, and many others, the choice is simple. For me, I am installing an electric pump only and gauge for under $600+- rather than replace the lift pump with the same thing for $550+. Easy choice.

I do admit that now that I have a few miles in the rearview mirror, I should have investigated a strange leak that I had. Two times while parked on a rather steep hill in front of my house, I had fluid under the coach when I left.

I smelled it, I rubbed it, I looked at it as closely as I could..... and decided it was.... truth is that I couldn't decide. My best guess is that it was oily water run-off. I was using my rose colored glasses and thinking there was a pocket of water in the frame somewhere that leaked out once I parked at such a steep grade. In hindsight I now know that was diesel coming out of a leaking lift pump gasket. I should have addressed it right away and that would have certainly been to start with the gasket -- and if that didn't fix it I probably would have been tempted by FASS and AirDogs gimmickery.

But -- I think when I really started digging into it I would have left the two filters in place, installed an electric pump and left the existing CAPS return system in place. See the next post for my quick napkin math DIY electric pump setup.

[Alpine36]

I think we can all agree the OEM lift pump was problematic, a royal pita to change out and now they are manufactured in China. That said, it leaves two choices when they leak, or in my case fail to operate and leak. Either replace the OEM pump and hope it's a once and done thing, still knowing the fuel delivery is under negative pressure and the slightest fuel filter restriction could send you walking, or install a constant duty fuel pump.
I chose one that improves filtration, separates air from fuel, provides positive fuel pressure and is QUALITY made in the USA all for about the same price as the problematic OEM pump.
These Improvements are far from gimmickry.
What you choose to do is up to you, but IMHO fuel delivery to the CAPS pump is not a place to cut corners. I'll eat a few more hamburgers and lay off the Ribeyes for a while if budget is a concern, but again, to each their own.

OK, some have asked how to mount a fuel pressure gauge onto the fuel filter housing. There are two choices of gauges you'll need. If running the FASS or Dog, buy a quality positive pressure gauge, 0-30psi. 1/8' NPT.
If running the OEM pump, buy a quality negative pressure gauge, 0-30 psi. 1/8" NPT. Both will require this adaptor for the FS1022 style fuel filter housing with the plug port on top, 10mm o ring fitting threads. And yes, this fitting comes with the o-ring. DO NOT throw the old port plug away in case the gauge ever springs a leak...
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[Ljwt330]

I'd like to ask one more question in this thread.

We all are aware that when changing to a positive pressure pump, the electrical connection to the OEM lift pump needs to be disconnected and a resistance, like a simple relay, added to fool the ECM.

My question is this, if one installs the system so the OEM lift pump is by-passed with the fuel inlet/outlet lines, why not simply leave the OEM connection alone and let the pump run for it's short duration? Yes, it will be running dry, but that portion of the pump is not functional anyway.

Just a thought.

[Fffrank]

Originally Posted by JDaveB

Frank, do you believe the claims that these systems also remove entrained air from the diesel fuel? I think that is a benefit I can’t easily replicate with a pure fuel pump

Simple answer: no. How is air getting into your system in the first place?

This is a very interesting read that does validate that diesel fuel can contain air. but he also makes this statement:

The proofthat air bubbles are air and not vapor is that they
appear when there is very little negative pressure
involved. They also do not disappear after being
pressurized by a lift pump, unless of course the
pressure is high enough to compress them beyond
the point of visibility (about 50 microns or less).

The CAPS system accounts for air in the system by providing a return at the top for both excess fuel pressure and/or to purge air from the system. In fact, when I replaced my CAPS pump I was SHOCKED at how quickly it purged all of the air from the system and started back up. I don't think I cranked it for more than 10 seconds before it was running. After spending almost a week convinced I had air in my injection lines as the primary issue -- this confirmed instantly that my CAPS pump was in fact the culprit.

Can the FASS/Airdog system circulate more fuel through their return system? Obviously. But for what purpose? It never reaches the CAPS system to provide additional cooling and in my mind, tumbling it back down your filler neck seems like a way to introduce more air (and not less!). Either way, it's likely so insignificant either way to be a complete non issue.

[Alpine36]

Originally Posted by Ljwt330

I'd like to ask one more question in this thread.

We all are aware that when changing to a positive pressure pump, the electrical connection to the OEM lift pump needs to be disconnected and a resistance, like a simple relay, added to fool the ECM.

My question is this, if one installs the system so the OEM lift pump is by-passed with the fuel inlet/outlet lines, why not simply leave the OEM connection alone and let the pump run for it's short duration? Yes, it will be running dry, but that portion of the pump is not functional anyway.

Just a thought.

Sure, why not? Mine failed electrically and threw a fault code 278? That's when I noticed hard starting and the lift pump seeping and upgraded the pump.
Or by clipping two wires, adding two spade connectors and the relay you'll never have to hear that miserable "thing" rattle again.

[Fffrank]

Originally Posted by Ljwt330

Again, my research was limited and there may be something out there that is half the price, once all components are compared together. I understand your skepticism as well. If you know of pump/filter/connectors/hoses combinations that add up to a significant savings, that would be welcome information for all here.

Pump - $80 - Walbro 392 (85-90 gph @ 14psi)
Pump Fittings/Adapters - $15
Custom hose to bypass your previous lift pump - $40
Leave your existing filter heads in place - FREE
Use existing CAPS return - FREE

Total: $135

Try as I might, I can't think of a single thing this wouldn't do as well as the FASS system. But if you believe "polishing" and "radius cuts" and "silencing" are valuable: that's the beautiful thing about the free market. You've got choices!

[Mile Marker 42]

Originally Posted by Fffrank

Pump - $80 - Walbro 392 (85-90 gph @ 14psi)
Pump Fittings/Adapters - $15
Custom hose to bypass your previous lift pump - $40
Leave your existing filter heads in place - FREE
Use existing CAPS return - FREE

Total: $135

Try as I might, I can't think of a single thing this wouldn't do as well as the FASS system. But if you believe "polishing" and "radius cuts" and "silencing" are valuable: that's the beautiful thing about the free market. You've got choices!

I don't think anyone would be comfortable putting that fuel pump on.

[Fffrank]

Originally Posted by Mile Marker 42

I don't think anyone would be comfortable putting that fuel pump on.

Hahah -- it's not "sexy" but it's a very common pump for performance applications. I know it's used a lot in the pick-up world.

You can use a Holly Black if you prefer. They go for around $200 and are much prettier.

[Alpine36]

Speaking of gimmeckry, look at these fabulous babys I forgot I had! Think what these could do for your toads. I'd probably let em go for only $129.95. (Obo jk)

[JDaveB]

https://www.parker.com/literature/Ra...iesel_Fuel.pdf

Here is a link to the entire article from which you pulled the quote. The article is clear; air is entrained in diesel fuel, and a properly designed pump/filter system can substantially remove that air. The AirDog system is designed to do that - with air venting on the top of the filter housing and proper orifices

Dave

[mg2016]

Working on a Airdog installation. Having difficulty locating the two wires from the lift pump that need to be cut. Does the starter need to be removed to access these wires. I have looked closely but can't see above starter or below lift pump. Am I missing something.



Thanks

[zmotorsports]

Originally Posted by mg2016

Working on a Airdog installation. Having difficulty locating the two wires from the lift pump that need to be cut. Does the starter need to be removed to access these wires. I have looked closely but can't see above starter or below lift pump. Am I missing something.



Thanks

In most circumstances removing the starter motor gives better access to the lift pump. Not the silver bullet of access but it helps as the area is tight.

The plug you are looking for will plug into the bottom of the lift pump. If you want to cut them further upstream you will need to locate a wiring schematic specific to your coach and Cummins engine.

Mike

[lbw6303]

Under the old adage -- "if it aint broke, don't fix it" --- I would leave the lift pump wiring alone. That pump runs for 15-29 seconds at key on and then just sits there until the next time. all the while fuel is flowing around/through it to get to the injector pump. the 15-20 seconds that it runs will simply assist your Air dog pump for a brief time, but it won't get in the way when it;s just sitting there. By cutting and/or installing a jumper, you are trying to fool the ECM into thinking that the lift pump is there doing it;s thing even though you've disabled it. I installed a FASS system -- have 4000 miles on the install and didn't do anything to the lift pump. My 2 cents.