Cummins ISC 8.3 CAPS - Possible Alternative to FASS upgrade?
Curious question, has anyone considered or tried to A) fool the ECU into thinking the stock lift pump is still there and B) instead of installing a FASS pump, simply wired the stock / existing lift pump it to be on all the time when the engine is running?
This instead of all the trouble and cost of installing the FASS pump and related hoses, bypassing, etc. It seems to me that unless there's some technical reason my idea won't work, that this might be much simpler than all the re-plumbing, etc
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The difficulty of the install depends on what pump you install and your layout. On my conversion, I only had to disconnect two hoses, have two new made up (they were less than two feet long) and hook them up to the Fass pump. Install a relay on the wire to the lift pump (resistance load to fool the ECM) and find a power source for the Fass pump. Very easy!
Location: Over the next hill, around the next curve...
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I read this as an idea (Financially advantageous, if it would work!), to just keep the Lift Pump cycling/pumping the full time the engine was on - vs adding a separate full-time pump, such as the FASS...
But my wife explains to me that I often hear or read things in away not intended. (Or, am I wrong in what I just typed about that? Perhaps she said 'Oh Dear, you're always right - even when wrong.') (It's lonely in my world within a small mine...).
OP - Sorry if I miss interpreted your intent...
Best to all,
Smitty
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07 Country Coach Magna Rembrandt 45' ISX600 Roo II was our 04 Country Coach Allure 40' OnDRoad for The JRNY! Enjoy life...
First, as already mentioned, I don't think the pump motor is robust enough to be ON continuously. It is a relatively small motor which was designed/selected for very limited use. I think continuous use would burn out the motor in short order.
Second, the active pumping of the lift pump may actually impede fuel flow through it. Again, I have no data as to how much volume the pump is capable of producing, but it is likely far less that is need by the main pump when under operating conditions. The FASS system uses a 95 gpm unit as transfer pump. We all know that once the pump shuts off, the fuel is drawn through it by the main pump at whatever flow rate is required. What I don't know is if that path through the pump body is anyway impeded when the pump motor is in operation. Just something to consider.
Third, once the main pump takes over, excess fuel is returned to the tank through the lift pump. Possibly, this function is compromised if the pump itself is running.
Finally, and this is sort of an "intangible," this CAPS system has been around for so many years that if it was feasible and easy, as suggested, it would have been done by someone long ago. The fact is that main pump failures due to lift pump failures has long been the weak link in the system. I just believe that a competent diesel mechanic would have done such a modification somewhere along the line. It either hasn't been done for reasons which the layman isn't aware, or it was tried and it failed.
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Larry, Eileen, and Finley
2004 Alpine 36FDDS
Third motor home, first Alpine, no need for another.
First, as already mentioned, I don't think the pump motor is robust enough to be ON continuously. It is a relatively small motor which was designed/selected for very limited use. I think continuous use would burn out the motor in short order.
Second, the active pumping of the lift pump may actually impede fuel flow through it. Again, I have no data as to how much volume the pump is capable of producing, but it is likely far less that is need by the main pump when under operating conditions. The FASS system uses a 95 gpm unit as transfer pump. We all know that once the pump shuts off, the fuel is drawn through it by the main pump at whatever flow rate is required. What I don't know is if that path through the pump body is anyway impeded when the pump motor is in operation. Just something to consider.
Third, once the main pump takes over, excess fuel is returned to the tank through the lift pump. Possibly, this function is compromised if the pump itself is running.
Finally, and this is sort of an "intangible," this CAPS system has been around for so many years that if it was feasible and easy, as suggested, it would have been done by someone long ago. The fact is that main pump failures due to lift pump failures has long been the weak link in the system. I just believe that a competent diesel mechanic would have done such a modification somewhere along the line. It either hasn't been done for reasons which the layman isn't aware, or it was tried and it failed.
When I installed ours I just bypasses the stock lift pump and ran a new fuel line straight from the FASS pump to the secondary filter. From the secondary filter I also ran a new fuel line which goes straight into the CAPPS injection pump. I did not want to run pressurized fuel though the lift pump manifold. I know by doing this if the FASS pump fails I can't just switch back. I do know the engine will remain running if the FASS pump fails. I have already tested this so that is verified.
I am ready to start procuring hardware for my FASS upgrade on my 2001 HR Endeavor ISC 330. I live in Eastern NC but there are a few towns close that are authorized FASS dealers. I went into the closest shop to discuss, and while they are wanting to be helpful they are only familiar with pickup truck conversions. They called their "FASS distributor" and were advised I probably should go with the larger capacity pump due to the length of supply line to the FASS. I plan on putting the FASS pump directly in place of the primary filter back near the engine as I believe some of you have done. I believe everyone who has discussed this on this forum has used the smaller pump and it does just fine. I plan on bypassing the OEM lift pump and taking the FASS output to the secondary FS1022 due to the fact the pump on this vintage coach is not ULSD capable, althought no leaks or problems to date. Other than that I plan on starting with no other modifications except the relay for the ECM fooling, a electric guage with sending unit in the head of the FS 1022, and of course the FASS return line into the fill neck. Any comments on the shop's FASS pump size recommendation most welcome.
Thanks, Cliff. A special thanks to those who have posted so much of their experience and advice and even graciously said to call them for help if needed once I start.
I am ready to start procuring hardware for my FASS upgrade on my 2001 HR Endeavor ISC 330. I live in Eastern NC but there are a few towns close that are authorized FASS dealers. I went into the closest shop to discuss, and while they are wanting to be helpful they are only familiar with pickup truck conversions. They called their "FASS distributor" and were advised I probably should go with the larger capacity pump due to the length of supply line to the FASS. I plan on putting the FASS pump directly in place of the primary filter back near the engine as I believe some of you have done. I believe everyone who has discussed this on this forum has used the smaller pump and it does just fine. I plan on bypassing the OEM lift pump and taking the FASS output to the secondary FS1022 due to the fact the pump on this vintage coach is not ULSD capable, althought no leaks or problems to date. Other than that I plan on starting with no other modifications except the relay for the ECM fooling, a electric guage with sending unit in the head of the FS 1022, and of course the FASS return line into the fill neck. Any comments on the shop's FASS pump size recommendation most welcome.
Thanks, Cliff. A special thanks to those who have posted so much of their experience and advice and even graciously said to call them for help if needed once I start.
I used the bigger pump. It was about the same price and it came with 2 filters mounted to the pump housing. I just thought the bigger pump would perform better pushing fuel through 27 feet of -10 fuel line. Our FASS pump did have a return off the pump which was easily plumbed into the tank vent that is on top the fuel tank.
If it were me and I had an option I would mount the pump as close to the tank as possible. I know some folks do not have that much room but we did. I would also try and bypass the stock lift pump. Some folks pump fuel or pull fuel though it (lift pump) and have had no problems. I look at it like it's just once less thing to leak and screw up. When ya do this though there is probably no going back if the FASS pump craps the bed while you are on a trip. Good news is, at least in our case, once the engine is started the injector pump will still be able to draft fuel thought the FASS pump without it running. I tested this for a good 10 mins of engine runtime with the FASS in place but not pumping. I did not drive it though but I feel it would work ok till I was able to get another pump.
Bypassing the stock lift pump would be easy. If you have to mount in the rear you can remove the supply line from the primary fuel filter and then from the new FASS pump you can go straight into the secondary filter. Fuel leaving the secondary filter goes straight into the injector pump.
I mounted our pump close to the tank and replaced all the fuel supply lines with new. The fuel comes out of our tank and goes to the FASS pump. From there I have one new fuel line straight into the secondary filter bypassing everything. I also replaced the fuel line from the secondary filter to the injector pump. I then mounted a small pressure gauge on top of the secondary filter housing. I did not even touch any of the return fuel lines. As far as the original fuel supply lines I just blocked them off with fittings.
Thanks for the response. I agree the cost difference is insignificant. It's the first I have heard anyone actually mentioning going with the larger capacity pump. I think I will go with it as well. Currently my installation will be like yours except I have no room at the tank so plan on installing FASS in place of the current primary fuel filter. Whether sucking or pushing the FASS still has to deal with the distance between the tank and the motor, so their recommendation does have merit. It's tempting to just use the existing fuel lines but I'll probably bite the bullet and install new.
More later. Thanks again.
Since the OP is asking if there are possible alternatives to the FASS TS pump, I may have some new ideas that will be soon verified.
I have not posted this information since I have already installed the FASS TS pump in my RV (and I am very happy with that decision), but some of you may find the installation easier if you go with the AirDog-II-4G pump. (TBD)
I have been working with a 2000 Newmar Owner who has an ISC-8.3L-330HP engine and a Spartan Chassis; and he chose the AirDog II-4G-165GPH pump over the FASS-TS-95GPH pump.
Note: AirDog offers a smaller 125GPH pump for Dodge Diesel trucks, but the AirDog 165GPH pump is for Class 8 Diesel Truck. As such it is "beefier" in most respects.
Below is the flow diagram I have drawn up for his application, and the key thing about usind the AirDog-4G is that it operates differently than FASS.
FASS is a "constant volume" pump so it will work to always deliver 95GPH. It will always try to maintain 15-18PSI as well. As such, the FASS pump will return a lot of fuel to the tank when the engine is at idle and under heavy load, because your engine does not need all this fuel.
On the plus side, I like that FASS will constantly recycle and "polish" my fuel, because it's done a good job cleaning up the algae in my fuel tank, but on the downside you can't tell when your filters need changing, because the FASS PSI will not drop on the gauge as the filters fill up with debris. And with the high fuel return on the FASS pump you definitely need to run a separate fuel line back to the tank.
AirDog is a "demand flow" pump and if you have not heard this term before you are not alone. AirDog says a demand flow pump will only deliver a little more fuel to your injection pump than what it needs... "on demand." And AirDog techs say their pumps will not return much fuel the the tank... like the FASS pump will.
This may mean there are several advantages for us RV owners by going with AirDog if the following is true:
* Mount your AirDog in place of the Primary Filter. (Just like the FASS TS Pump.) But unlike the FASS pump you can "T" into the CAPS fuel return line located just behind the Lift Pump Manifold (aka Fuel Supply Manifold), only 8 ft from your pump, and this is because very little fuel is being returned to the tank.
* AirDog's PSI is supposed to drop lower as the fuel filter gets "used-up", which is nice, because that will tell you when it's time to change your filters. And AirDog's 4G Pump comes with a 5 or 10 PSI pressure switch that will light an LED you can easily mount on your dash to signal its time to change your fuel filters if you don't want to mount a digital gauge in your engine compartment or dash or you don't want to mount an oil filled gauge above your #3 Filter. (Which I recommend, if you an easily see this gauge when you do your pre-trip walk-around-check before hitting the road. And because it only costs $20.)
Note: If you have a #3 filter on a Spartan chassis then you might not be able to see the oil filled gauge very easily. But on my Winnebago, my #3 filter (which is my old #2 filter before I added FASS) is easily visible from inside my engine compartment.
Both AirDog and FASS can be easily mounted right where your primary filter is located. This will let you re-use your existing fuel lines, and there is no good reason you need to mount either of these two pumps close to the fuel tank... as everyone says.
This is because both manufactures have increased the pump size and wire gauge and they are more efficient than earlier versions. Just make sure you don't mount the pump more than 3 feet higher than the sump of your tank you will be okay.
Note: I have not installed the AirDog-4G, but I believe in another 3 weeks we will hear from an owner who has. And at that time he can report his findings in an new thread.
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If the AirDog-4G-165GPH pump does not return very much fuel to the tank...
And if the AirDog PSI will drop based on "demand flow" technology or principles...
Then it's very likely the pressure into the injection pump will be less than 25PSI during the first 30 seconds when your stock fuel pump is switched "on" by the ECM and then switched "off" by the ECM 30 seconds later. ...Why is this important?
Answer: If you don't have more than 25 PSI "dead head" to your Injection Pump, it begs the question: "Why go to the trouble and expense of both by-passing the lift pump manifold and by-passing the lift pump electrical leads and installing a relay to fool the ECM?"
When I took my RV to Freightliner to by-pass the lift pump they charged me $350. So maybe with the AirDog you don't have to bother with this step? (TBD) Let's wait to see what this other owner has to say after he installs an AirDog-4G pump according to this diagram.
Thanks for the response. I agree the cost difference is insignificant. It's the first I have heard anyone actually mentioning going with the larger capacity pump. I think I will go with it as well. Currently my installation will be like yours except I have no room at the tank so plan on installing FASS in place of the current primary fuel filter. Whether sucking or pushing the FASS still has to deal with the distance between the tank and the motor, so their recommendation does have merit. It's tempting to just use the existing fuel lines but I'll probably bite the bullet and install new.
More later. Thanks again.
It's always easier for a pump to push fuel rather than pull fuel. With that being said I think it will be ok mounting in the rear. All the pump has to do is supply volume. If the FASS pump only produced 2 PSI to the injector pump it would still work just fine hence the name "lift pump". Not sure what RV you have. We have a Monaco Camelot and at first I thought we would have to mount in the back. I found that the panels that cover the fuel tank fill can be unfastened with screws on the bottom and swing up out of the way like a regular door. Just have to tie it up to keep it out of the way. I was able to mount the pump on the bulkhead divider. Maybe I was just lucky.
If you do decide to go with new lines some have used hydraulic hose which is fairly expensive. I used PTFE with a SS braided covering. When done correctly the PTFE will hold about 1K PSI.
AirDog Electric Pump (An Alternative To FASS-TS-95GPH)
Another owner just installed an AirDog-II-4G-150GPH pump in his 2002 Nemar/Spartan Chassis (8.3L) and he is quite happy with his installation. For more information you can visit his thread at:
There are several differences between the AirDog "demand flow" pump and the FASS-TS "constant volume" pump you might look into.
Both pumps achieve the primary goal of providing positive fuel pressure to the injection pump (CAPS in this case). However, the AirDog returns ~10x less fuel to the tank. Therefore, installation may be easier if you don't want to run a 38' fuel return line to the tank -- like you have to do with the FASS pump.
On the other hand, the FASS offers "fuel polishing" benefits over the AirDog, if you buy into this sort of thing? I tend to think it's worthwhile, but that's just my opinion.
The AirDog pump costs a bit more, but the FASS installation requires 38' feet of hose to run a fuel return line to your tank and that will run you $125 more. So both pumps bear the same approximate part cost in the end. However, the AirDog may save you 2 hours of installation time. So in the then the part costs will be very similar.
Note: You really do not have to run a digital fuel pressure gauge to your dash. This is a desirable option, but it will cost you $150 and another 2-3 hours of installation time vs. buying a $15 gauge on Amazon and a 10mm to 1/8"NPT adapter so you can mount an oil filled gauge on top of your filter block.
In both cases you need to disconnect the electrical wires from the ECM to the Lift Pump. So unfortunately, that will not change.
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