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Convince me that I need a Fuel Air Separation System


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Ok, so I totally get that the CAPS pump operates under vacuum, and that's bad for it and can/does lead to a lot of expensive failures.

As I understand it, the 'problem' is that the CAPS is working against a vacuum, so pushing fuel under positive pressure to the injection system should address the issue. And a lot of folks install a FASS or Airdog system for that reason. 

But I'm not convinced that I have a big problem with entrained air in the fuel. And my filters don't get clogged a lot, so I'm not real motivated to go out and buy a fuel polishing system.

Why not solve the CAPS problem with a pressure-regulated pump at the tank, and otherwise leave my fuel system as-is?

I've read a few write-ups of folks that have taken this route. Looks to me like a pump would be at least couple-hundred $$ less than an air separation system and somewhat easier to install. 

Is there something I'm missing?

Thanks

Walter

Edited by wamcneil
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I’ve seen those on Ultra RV site but never gave them any consideration. So for DIY’rs  it’s probably around $300 less after install out of pocket and less work, but it’s not polishing. With fuel prices and some of us not driving as much and sitting more I kinda like the ability to polish to some degree. But it’s an option for sure. 

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25 minutes ago, tmw188 said:

I’ve seen those on Ultra RV site but never gave them any consideration. So for DIY’rs  it’s probably around $300 less after install out of pocket and less work, but it’s not polishing. With fuel prices and some of us not driving as much and sitting more I kinda like the ability to polish to some degree. But it’s an option for sure. 

Easy to install. Didn’t have to run a return line. It was one of the first mods I did. Took all of 2 hours 

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1 hour ago, wamcneil said:

But I'm not convinced that I have a big problem with entrained air in the fuel. And my filters don't get clogged a lot, so I'm not real motivated to go out and buy a fuel polishing system.

Why not solve the CAPS problem with a pressure-regulated pump at the tank, and otherwise leave my fuel system as-is?

I've read a few write-ups of folks that have taken this route. Looks to me like a pump would be at least couple-hundred $$ less than an air separation system and somewhat easier to install. 

Is there something I'm missing?

Thanks

Walter

Walter,

I do not know if it is the 'Polished, airless fuel' or the 'positive pressure' to the inlet of the CAPS pump, but I can hear a "tone-al" difference and feel a smoother idle with the FASS system operating. 

Possibly, just having a 'fulltime' lift pump would have the same effect.   Another part of the puzzle may be the price of, and access to, the factory lift pump (that does not run fulltime (by design)) compared to a remotely located aftermarket pump (or pump-filter system).

When I bought my DP, I had such dirty fuel (black like ink) and a leak at my factory lift pump, that I opted for the full filtering-return fuel-lift pump system. 

Ken

 

15 minutes ago, wamcneil said:

Ok... Maybe a more cost effective pump might suffice?

The pump would only need to output 50 GPH (about 3x actual fuel flow) and hold 5 to 10psi to keep the CAPS pump in the "positive world"...

Ken

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1 minute ago, JDCrow said:

You would still need to trick the CPU into thinking the lift pump is present and still active

That's as easy as a resistor across the two pins of the connector at the factory lift pump

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I thought there was polishing going on even with the original stock set up.  Doesn't the fuel go through the filters and then most of it returns to the tank?

How about just a regular ol 12v fuel pump installed near the tank.  That should push the fuel to and through the lift pump with positive pressure at the CAPs pump.

From what I understand, fuel return is at least in part to cool the CAPs injector pump polishing is a side benefit

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4 minutes ago, Ray Davis said:

I thought there was polishing going on even with the original stock set up.  Doesn't the fuel go through the filters and then most of it returns to the tank?

How about just a regular ol 12v fuel pump installed near the tank.  That should push the fuel to and through the lift pump with positive pressure at the CAPs pump.

From what I understand, fuel return is at least in part to cool the CAPs injector pump polishing is a side benefit

There is "filtering" going on in the stock setup, there is only short term (at engine start) pressure to the CAPS pump, but no fuel is returning to the tank until it passes thru the CAPS pump/system.  On top of that, the CAPS pump has to 'suck' it's fuel thru a 1/2" hose almost 30' long.... I do not think Cummins really was 'consulted' on having their engine mounted that far from the fuel source, with their 'normal' installation components. 

You are right, any 'regular old' pump pushing fuel to the engine from the tank would be an improvement.

Ken

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17 minutes ago, Cubflyer said:

That's as easy as a resistor across the two pins of the connector at the factory lift pump

Yeah over my head, hence the kit purchase.  It was all set up to the proper pressure as well. I didn’t have to think much, which tends to be a good thing at times 😜

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Posted (edited)
27 minutes ago, JDCrow said:

You would still need to trick the CPU into thinking the lift pump is present and still active. 

That'd need to be done with a FASS system also though, right? 

(Edit) Ah. That's nice. I didn't realize the kit would plug in place of the factory lift pump.

Does the original lift pump need to be disconnected? Or just if the new pump is located in the back and installed between the primary and secondary pumps?

I'm inclined to put mine up front at the tank and leave everything alone in the back by the engine.

Edited by wamcneil
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15 minutes ago, wamcneil said:

That'd need to be done with a FASS system also though, right? 

(Edit) Ah. That's nice. I didn't realize the kit would plug in place of the factory lift pump.

Does the original lift pump need to be disconnected? Or just if the new pump is located in the back and installed between the primary and secondary pumps?

I'm inclined to put mine up front at the tank and leave everything alone in the back by the engine.

No, I bought threaded caps and plugs and hosing to bypass the lift pump. 
 

I installed my kit right next to the filter in the side compartment, behind the condenser unit. That way the hoses were easy to cap of and run to the lift pump. I don’t have my coach with me, I’ll see if I can dig up pics of my install 

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21 minutes ago, wamcneil said:

I'm inclined to put mine up front at the tank and leave everything alone in the back by the engine.

One of the 'problems' with leaving everything alone back by the engine is that the stock lift pump has a history of leaking where the pump bolts to the housing, That is where my pump was leaking and it is very common. 

I completely bypassed the "supply'  fuel around the original lift pump using the existing flexible hose that went to the housing and a #10 union to connect it to the metal tube that came out the front of the housing and goes to the final filter mounted on the side of the engine just upstream of the CAPS pump.  Simple to do... (I also used a union with an 1/8" NPT port to give me a place to register fuel pressure)

Ken

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14 minutes ago, Cubflyer said:

One of the 'problems' with leaving everything alone back by the engine is that the stock lift pump has a history of leaking where the pump bolts to the housing, That is where my pump was leaking and it is very common. 

I completely bypassed the "supply'  fuel around the original lift pump using the existing flexible hose that went to the housing and a #10 union to connect it to the metal tube that came out the front of the housing and goes to the final filter mounted on the side of the engine just upstream of the CAPS pump.  Simple to do... (I also used a union with an 1/8" NPT port to give me a place to register fuel pressure)

Ken

Yeah I’d have to look at pics to remember how I ran it. Was over a year ago and have since moved my mind into other projects. 
 

I know I intercepted the fuel line right after primary filter and ran it to the new FASS pump. Then a new hose over. I’ll try and dig it up here in a bit 

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4 hours ago, Cubflyer said:

One of the 'problems' with leaving everything alone back by the engine is that the stock lift pump has a history of leaking where the pump bolts to the housing, That is where my pump was leaking and it is very common. 

Good point!

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When my original lift pump started leaking I tightened the 3 bolts on top to stop the leak.  Fortunately I was at home with the rig parked and had time to think about my options.  I spent copious amounts of time reading/research.  There were dozens of posts on IRV2 of people installing the FASS or Airdog systems. At the time not many posts on the Monacoers site but some.

There are posters on both IRV2 & Monacoers that I follow knowing that their advice is rock solid.  Although I didn't keep a tally it seemed that most people who did an upgrade of the original lift pump opted for the FASS system, with the main reason being the fuel polishing. 

Back years ago when I changed my fuel filters I had a bad case of algae, a black stringy slimy mess that almost completely clogged my fuel filter.  That's when I started using Biobor.  But thinking about how much time my rig sits and the potential for getting a bad tank of fuel. 

Weighing all the info I read and wanting to upgrade to the best option I decided on a FASS system for fuel polishing and air removal.    I ordered one from Parley's (no tax and free shipping) and it cost $649 last May.  All in with hoses, fitting, and fuel gauge I had ~$950 in my install. 

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Thanks all.

I'm certainly not opposed to the fass/airdog systems. But I've already got a pretty robust filtration system and I just don't think I need a new one. If this were a modded pickup with weak factory filtration, I think the combined lift pump & primary & secondary filtration system would be compelling. 

I think that cheap PPE pump I linked would work fine, but diesel forum folks complain about frequent failures and I don't think I want to take a chance on it...

So now I'm thinking about Airdog's Universal Raptor 100 gph pump for $317. 

Thanks

Walter

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My lift went inop also, after much research and debate I found that the new diesel fuel additives are mostly ethanol based and have a very high acidic base. This causes the gaskets and the pump impeller metal plate to erode and fail. 
 

After a lot of reading and consulting with Cummins Diesel mechanics, I found out the latest lift pump for my ISC 350 (made under contract with Cummins in China) has a neoprene based gasket and a corrosion resistant impeller plate in it. Priced it around the US from Cummins dealers, best price was Cummins of Tuson (can't spell) AZ. With shipping under 400 bucks, around Jan 2021. 
 
Not a easy first time install, you have to go in from the top and work around the turbo, requires someone (my son) with LONG Arms. Got the Cummins parts warranty, the only thing that caused mine to fail was the new blended fuel  ️  Runs perfect now, took about four hours since it was our first replacement. Two hour job for a skilled long arm tech that's familiar with the system

I went back with stock reasoning that the first lift pump lasted 22 years (2000 Dynasty) and at my age ( classified-lol) the replacement stock pump would work and save a few bucks and last longer than me probably 

 

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4 minutes ago, Viper04 said:

I went back with stock reasoning that the first lift pump lasted 22 years (2000 Dynasty) and at my age (classified-lol) the replacement stock pump would work and save a few bucks and last longer than me probably.

My original lift pump was replaced in the Windsor back in April 2015. But that was only after a Cummins service tech had finished replacing the Coolant Filter Housing that had gotten cracked by a Speedco service tech. He hooked the engine ECM up to his computer system and read a bunch of fuel error codes. He looked further into the operation of the engine and found a very slight leak coming from the lift pump. It wasn't even leaking enough diesel fuel to see any on the ground. It was dripping onto the starter and staying there. Knowing that additional information, I had him replace it versus risking a CAPS failure later. The new lift pump has now been running error free for the past 7 years whereas the original one lasted 14 years.

I think the new owner shouldn't have any problems hopefully.

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Does this look like it’s original? It looks like it could have been replaced by the label and the two of the three bolt heads doesn’t look original either, as if they are star style? 

6F09E806-64C7-440E-917C-7AC76E735FBA.png

CF77026E-A3F2-4F0D-9F55-B90DAA0A06CB.jpeg

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Just to add, I know bolt heads aren’t necessarily any indicator and a new pump probably doesn’t come with new bolts, but of all the pictures I’ve seen are all hex bolts. 

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Ok, so I've been talking to airdog support. They have a cummins harness that looks like it may save me a bunch of work. It's got a plug to go in place of the factory lift pump, but their tech support didn't know if it would run the pump full-time.

As I understand it, the ECM runs the lift pump for 30 sec at startup, right? And then it shuts down the pump.

But it apparently holds a voltage on the pump and will throw an error code if the pump isn't detected. So folks install a 'dummy' relay to fool the ECM into thinking the pump is present.

Does anybody know if that pump-check diagnostic signal is sufficient to keep the relay engaged?

If so, it sounds like this harness would keep the pump running all the time by virtue of whatever diagnostic voltage is held on the lift pump. I guess if that doesn't work out I could modify the harness to trigger from a different ignition source.

Here's the diagram:

image.png.aacd67255598b8f0616aab90f47bb477.png

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32 minutes ago, wamcneil said:

Ok, so I've been talking to airdog support. They have a cummins harness that looks like it may save me a bunch of work. It's got a plug to go in place of the factory lift pump, but their tech support didn't know if it would run the pump full-time.

As I understand it, the ECM runs the lift pump for 30 sec at startup, right? And then it shuts down the pump.

But it apparently holds a voltage on the pump and will throw an error code if the pump isn't detected. So folks install a 'dummy' relay to fool the ECM into thinking the pump is present.

Does anybody know if that pump-check diagnostic signal is sufficient to keep the relay engaged?

If so, it sounds like this harness would keep the pump running all the time by virtue of whatever diagnostic voltage is held on the lift pump. I guess if that doesn't work out I could modify the harness to trigger from a different ignition source.

Here's the diagram:

image.png.aacd67255598b8f0616aab90f47bb477.png

I'm surprised that Airdog doesn't have that answer. 

Need information on the relay that they use as to what voltage it needs to work. 

If this does work it wold save a bunch of time, my only concern is the interaction with the ECM.  It would be a costly experiment if it screws up the ECM. 

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Posted (edited)

Not real concerned about the ECM... I'm pretty sure it's just a standard bosch-type automotive relay.

Same type that folks use in FASS installs as a dummy load to fool the ECM into thinking the factory lift pump is still present.

 

Edited by wamcneil
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