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Discussion Starter #1
This pertaining to a 2004.5 LLY. I'm sure I'm overthinking this but never hurts to ask the expertise around here for insight.

Ok I have read enough to see a 'always on' gravity feed aux tank is apparently a bad idea (gravity feed into the fill neck with the RDS 'float' valve that prevents overfilling) It's a cool kit and thought, but apparently a bad idea? and causes the truck to throw codes and such? THAT is unacceptable!! Not going to deal with clearing codes and shut downs to get the fuel gauge working even though I have a Edge CTS and it's easy. iMO any time you throw bad info at a ECM that causes a fault / code,, it is going to cause more headaches and problems with other systems further down the road. PLUS not sure I would 100% trust the float ball system to not overfill and spill 50 gallons of fuel out under the truck / trailer.

REGARDLESS.... I'm wondering if the code is caused by the tank VENT. If I were to tie the in-bed AUX tank vent in to the vent line running from the truck tank to the fuel fill door,, would THAT solve the code issue?????

I guess the question is more ,, does the Duramax fuel system put vacuum to the fuel tank like the gas rigs to purge fuel vapors (and the infamous emissions / fuel cap code)? Is THAT part of what is causing the code when using a 'always on' gravity flow aux tank??

The thought being if the gravity flow is into the fill neck, and the AUX tank is vented to outside air, you could not put a vacuum on the system as the aux tank would always feed and you couldn't get negative pressure. is the lack of vacuum causing the code???? Would that be eliminated if the vent were connected to the truck tank vent line???

Even using a shut-off valve at the AUX tank outlet, should the AUX vent and the truck tank vent be tied together for when you DO gravity feed into the truck tank???

In a race car we drop the vent line over the side of the cell with roll-over valve and a old fuel filter on the end so bugs can't get in,, and vent to the air. The LLY is a little different animal and looking for the SMART way to do this.

(This is the float valve connection kit I have: https://www.northerntool.com/shop/tools/product_200315503_200315503 )
 

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This pertaining to a 2004.5 LLY. I'm sure I'm overthinking this but never hurts to ask the expertise around here for insight.

Ok I have read enough to see a 'always on' gravity feed aux tank is apparently a bad idea (gravity feed into the fill neck with the RDS 'float' valve that prevents overfilling) It's a cool kit and thought, but apparently a bad idea? and causes the truck to throw codes and such? THAT is unacceptable!! Not going to deal with clearing codes and shut downs to get the fuel gauge working even though I have a Edge CTS and it's easy. iMO any time you throw bad info at a ECM that causes a fault / code,, it is going to cause more headaches and problems with other systems further down the road. PLUS not sure I would 100% trust the float ball system to not overfill and spill 50 gallons of fuel out under the truck / trailer.

REGARDLESS.... I'm wondering if the code is caused by the tank VENT. If I were to tie the in-bed AUX tank vent in to the vent line running from the truck tank to the fuel fill door,, would THAT solve the code issue?????

I guess the question is more ,, does the Duramax fuel system put vacuum to the fuel tank like the gas rigs to purge fuel vapors (and the infamous emissions / fuel cap code)? Is THAT part of what is causing the code when using a 'always on' gravity flow aux tank??

The thought being if the gravity flow is into the fill neck, and the AUX tank is vented to outside air, you could not put a vacuum on the system as the aux tank would always feed and you couldn't get negative pressure. is the lack of vacuum causing the code???? Would that be eliminated if the vent were connected to the truck tank vent line???

Even using a shut-off valve at the AUX tank outlet, should the AUX vent and the truck tank vent be tied together for when you DO gravity feed into the truck tank???

In a race car we drop the vent line over the side of the cell with roll-over valve and a old fuel filter on the end so bugs can't get in,, and vent to the air. The LLY is a little different animal and looking for the SMART way to do this.

(This is the float valve connection kit I have: https://www.northerntool.com/shop/tools/product_200315503_200315503 )
I've been using that gravity feed for 5 years without a problem. It does not
set any codes. The fuel gauge will go to empty if you are driving long distances without stopping ( somewhere around two hours or so). But if you stop for a pee break the fuel gauge resets itself. I didn't do anything with the tank vent.

Diesels don't have vacuum (generally speaking), unless it's for Cali emissions on early models.
 

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Discussion Starter #3
Hahahah with MY wife,, 2 hours between pee breaks would be a HUGE improvement. In a 250 mile trip she is 'commanding' me to pull over about every 75 miles :( Takes us FOREVER to get anywhere. But what ya gonna do!

My 04.5 did have the Cali emissions before the 5 level tune and the normal item deletes (Cat, EGR etc) SO maybe the 2 smaller lines coming from the tank to the fill door are just vents???) So the guys calling out codes along with the fuel gauge issue are apparently newer trucks,, (I had to go back and read more thoroughly at the posters sig)

How did you vent the AUX tank? My RDS tank has a vent w/ rollover valve but was thinking of venting it into the fill neck along side the gravity feed. Bad idea?
 

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Hahahah with MY wife,, 2 hours between pee breaks would be a HUGE improvement. In a 250 mile trip she is 'commanding' me to pull over about every 75 miles :( Takes us FOREVER to get anywhere. But what ya gonna do!

My 04.5 did have the Cali emissions before the 5 level tune and the normal item deletes (Cat, EGR etc) SO maybe the 2 smaller lines coming from the tank to the fill door are just vents???) So the guys calling out codes along with the fuel gauge issue are apparently newer trucks,, (I had to go back and read more thoroughly at the posters sig)

How did you vent the AUX tank? My RDS tank has a vent w/ rollover valve but was thinking of venting it into the fill neck along side the gravity feed. Bad idea?
I just vented to atmosphere. I suppose you could vent it to the tank but I don't think you need to.
 

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Discussion Starter #5
Thanks. I'll do some more research on the Cali emmission for this LLY and see if there was some vapor purge vacuum pump BS and if so I'll tie into the truck tank vent,, but I'm suspecting when Rob did the tune a lot of that BS went away,, as much as was LEGAL that is ;0
Thanks
 

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There is NO Vapor purge on the fuel tank on a 04.5 -05 Calif.
Yes, my large tank did cause the fuel light to come on and the gauge went to empty during the first year I had the tank- Guess it finally learned and has not done that in a long time- It did not set codes or affect the running- I just drove on and after 100 miles or so, it corrected itself.
 

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I've got a 2018 3500 D/A that's equipped with a RDS Aux Fuel Tank/toolbox combo. The fuel tank is 40 gal with a toolbox section on top. On one end of the toolbox is a section that's walled off from the rest of the toolbox and contains the fuel tank fill connection, level gauge (very inaccurate), and a vent fitting that has nipple open to the surroundings. The tank has a manual isolation on the outlet that's outside of the tank and can be reached from the bed of the truck. There's also a solenoid shutoff valve that I control from inside the cab with a toggle switch. If I'm going to use the aux tank I'll have the manual isolation open, but the electric shutoff closed initially. When I see the fuel gauge on the dash come down to the full mark (it's usually pegged out high after filling the tank), I'll open the electric shutoff. The aux tank gravity feeds into the neck of the normal fill connection and i've never had any issue with codes, fuel gauge indications or anything.
It's nice to be able to go a days worth of distance without having to get fuel (although we do stop for other reasons) as it's sometime difficult to find a station I can get the truck & trailer into (and back out of). Can always use truck stops, but they have their own conditions to deal with...
 

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Discussion Starter #8
Shadow that's actually the tank / box I REALLY wanted,, but just couldn't bring myself to throw $800 (with shipping) at it,, and throw away the cross-bed tool box I already have. So I just added a 45 gallon vertical tank in front and slid the tool box back the 11 inches. I have some thin aluminum diamond plate to make some trim plates to finish out the top of the bedside in front of the bok. (will make it look like it belongs anyways) The 45 gallon tank has the low gravity outlet w/ ball valve, a siphon feed outlet on top, a vent with roll over, locking fill cap and the large pipe fitting for a transfer pump. Your electrical shut-off solenoid is normally closed when key is off, and opens at key on??? Is that correct?

What's everyone doing for filtration between the aux tank and the filler neck??? I was thinking just a small 10micron screen-filter in the 3/8" hose between the ball valve and the fill neck. Don't have a lift pump and filters scrubbing the fuel, just keep good fresh Baldwin filter in the stock filterhead, so want to keep the 'chunks' out of the truck tank.
 

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What's everyone doing for filtration between the aux tank and the filler neck??? I was thinking just a small 10micron screen-filter in the 3/8" hose between the ball valve and the fill neck. Don't have a lift pump and filters scrubbing the fuel, just keep good fresh Baldwin filter in the stock filterhead, so want to keep the 'chunks' out of the truck tank.[/QUOTE]

I didn't add a filter between the aux tank and the main tank. I believe that's what the stock filter is for.
 

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Your electrical shut-off solenoid is normally closed when key is off, and opens at key on??? Is that correct?
Yes

[/quote]What's everyone doing for filtration between the aux tank and the filler neck??? I was thinking just a small 10micron screen-filter in the 3/8" hose between the ball valve and the fill neck. Don't have a lift pump and filters scrubbing the fuel, just keep good fresh Baldwin filter in the stock filterhead, so want to keep the 'chunks' out of the truck tank.[/quote]

i'm just running a small in-line filter; clear plastic
 

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Marv - It looks like I have the same locking cap as you, they are vented so you don't need to vent your aux tank. I am running a small fuel pump (has a small filter), then pass through a golden rod water blocker filter (probably not required but thought I didn't want to worry about water) then a 12v NC solenoid and into the tank via the fill line using the same kit in your Northern tool link. Here are a few pics, I don't seem to have one that shows the solenoid but its right downstream of the filter. I have been waiting until the truck's tank is about 1/2 full then turn on the pump and let it fill till the gauge reads ~3/4 full. When I shut the pump down it normally settles out at about 7/8 full. I have not had any issues throwing codes. My understanding is that it will throw a code if you don't let the tank level drop some which is why I don't switch it on until 1/2 empty and all is good....
 

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Marv - It looks like I have the same locking cap as you, they are vented so you don't need to vent your aux tank. I am running a small fuel pump (has a small filter), then pass through a golden rod water blocker filter (probably not required but thought I didn't want to worry about water) then a 12v NC solenoid and into the tank via the fill line using the same kit in your Northern tool link. Here are a few pics, I don't seem to have one that shows the solenoid but its right downstream of the filter. I have been waiting until the truck's tank is about 1/2 full then turn on the pump and let it fill till the gauge reads ~3/4 full. When I shut the pump down it normally settles out at about 7/8 full. I have not had any issues throwing codes. My understanding is that it will throw a code if you don't let the tank level drop some which is why I don't switch it on until 1/2 empty and all is good....
do you have details on what fuel pump/filter you have? I've been thinking about adding one as the gravity drain rate slows as the aux tank empties.
 

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You guys running gravity feed might check your state laws, most of the states it's illegal to use gravity feed, there has been many discussions on this.
Vent would be a good idea, what if for some strange reason the cap vent goes bad, every tank has some sort of venting beside just relying on the cap.
Have a inline filter would be very smart just in case, I wouldn't want my stock filter to get plugged up sooner than normal, PITA to get to, to change.
You guys can look up the EPA guidelines on this, I've posted it enough times the past couple of years.
 

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I have the RDS 60 gal with tool box combo, probably closer to 50 gals from what I’ve calculated fueling up when new/empty.
 

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yes I tried the gravity feed but with the filter it too slow. Tied both the pump and the solenoid into a lighted toggle to help remind me its on. powered via a retained accessory power outlet on the driver side fuse panel in the cab - pics of switch install attached



pump is here

https://www.princessauto.com/en/detail/12v-electric-fuel-pump-solid-state-posi-flo/A-p8606261e

Filter is here

https://www.princessauto.com/en/detail/3-4-in-water-absorbing-fuel-filter-assembly/A-p2460036e
Thanks, much appreciated
 

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I always suggest using ignition on power for a aux tank pump, if you happen to forget to turn it off when shutting the engine off, the pump will also turn off.
 

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Discussion Starter #18
the RDS tank fill cap is vented for 'vacuum' only as I understand, but have not checked in to it really for sure.. As I understand,, when the level drops it lets air in to avoid collapsing the tank. But is 'in' only and has a spring loaded valve to keep fuel from sloshing out?? (That's from a description I found on th ereplacment cap)

I live in Az where in the tank may see high 70s at night and in the sun see 125°+ during the day. The expansion of the fuel is my concern for venting. If the cap won't let the vapors out,, I want to do it to a controlled area where it won't make a mess,,,, or be subject to monsoon dust storms, or buggs. We have a bee here that simply LOVES to pack bougainvillea flowers into every open tube and hose / fitting they can find. So I need to vent to an enclosed area, or hang a cheap filter on the end of the vent tube. Either is easy enough but wanted to make sure I don't cause any self inflicted headache with the Cali emissions on this thing.

OK last dumb question.... I found in a thread one setup using a Facet cubes pump. Liked that they specifically list it's compatible with diesel and Bio- diesel,, alcohol,, bla bla bla. Besides cost,, the amps it takes to run for the GPM seemed really efficient , Made in USA, and has a replaceable 74micron filter built in, and a 'anti-siphon valve so it acts as an electric shut-off. Pretty much seems to take care of all of the needs for only $106 right???

https://www.pegasusautoracing.com/productdetails.asp?RecID=8674
 

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OK last dumb question.... I found in a thread one setup using a Facet cubes pump. Liked that they specifically list it's compatible with diesel and Bio- diesel,, alcohol,, bla bla bla. Besides cost,, the amps it takes to run for the GPM seemed really efficient , Made in USA, and has a replaceable 74micron filter built in, and a 'anti-siphon valve so it acts as an electric shut-off. Pretty much seems to take care of all of the needs for only $106 right???

https://www.pegasusautoracing.com/productdetails.asp?RecID=8674
I've also been looking at the Facet pumps and trying to figure out which to get. I have found that some have a better price on Amazon than other sites. Here's one I'm trying to figure out if it would work ok:

https://www.amazon.com/dp/B071H73QBX/?coliid=I1PF9E738A2D35&colid=308E61PJ7RWGC&psc=0&ref_=lv_ov_lig_dp_it

Here's a link I ran across on Facet pump info:

https://www.pegasusautoracing.com/group.asp?GroupID=FACET

For some reason on this chart they don't give the same specs for the pumps so comparison is tough.

One of the things I've been trying to figure out is whether the tank will still gravity drain with the pump off. A little would probably be OK, but I wouldn't want it flow like it would with no pump there.
 

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Discussion Starter #20 (Edited)
Some of the Facet pumps DO and some DONT. It looks like NONE of the Posi-flow act as a positive shut-off

Here's a link to the Facet - Purolator site for the posiflow specs

http://www.facet-purolator.com/tech-information/

Some of the few that are a 'shut-off' seem to be replacement for diesel generators in motorcoaches. We are on the same thought,, the one i linked has a replacable filter (70 micron or 400 micron) and does act like a chutoff solenoid valve. Kind of everything in one with ONE switch and one set of connections to leak. I'm not thrilled with the $106 but in reality by the time if find a normally closed solenoid valve, and a pump, anda filter, and fittings and wiring. All in one for $106 may not be unreasonable at all. LOL
 
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