Fuel Tank Questions

[BERT E SHETLER]

2004.5 4x4 6 speed manual
Hey everybody.
I've really learned a lot about this truck here, thanks to you guys.
This project:https://www.turbodieselregister.com/threads/preparing-for-a-pretty-big-trip.272221/ is what I'm dealing with now, but I wanted to start a new thread due to the fact that it all went down a road I didn't expect to be on.
I installed the PacBrake that was recommended, and it works as expected.
I decided against a rack of gauges that I potentially would have been wasting money upon.
Instead, I installed the BD Low fuel pressure warning light. Cheap and reliable.
I have found that the OE filter mounted lift pump has been replaced with the in-tank pump previous to my owning the truck.
So,,, after installing the alarm LED, I keyed up the pump a few times to purge the air, the light went out as expected. BUT what I didn't expect was that under normal driving conditions, driving around the neighborhood, the light comes on almost all the time. So this means I'm running under 5 psi fuel pressure all the time.

So, today I dropped the tank and ordered up a new in tank lift pump.
Now that the tank is out of the truck, I've found that there are 3 unused ports that are just open to the atmosphere. There aren't any other hoses connected, just the pressure line, the return line and the electrical connector. I intend to plug these before replacing the tank, but then I was wondering if I need a vent line?? No idea why these are there, or what they were for. Maybe it's a junkyard tank from a gas truck?
I will try to post a picture.
Any opinions and advice is welcome.
Cheers
Bert

 

[Ozymandias]

These are breathers, you can connect them with some rubber hose and Tee's and put a small engine fuel filter at the end.
But you shouldn't overthink it, it's no big deal.

 

[BigPapa]

Ozy’s correct, they’re vents. I’d make sure they’re open. Beyond that I’d leave them alone.

 

[BERT E SHETLER]

Okay! Thanks for the info. I think I'll do like Ozy said. a little vacuum line and a cheapie filter will give me a little peace of mind.

 

[petersonj]

BUT what I didn't expect was that under normal driving conditions, driving around the neighborhood, the light comes on almost all the time. So this means I'm running under 5 psi fuel pressure all the time.

Unfortunately, most pressure switches for automotive use can have a large variance in actual pressure versus advertised pressure unless you buy a very high dollar pressure switch. If you can even find detailed specs for a pressure switch, they will usually say something like, "pressure switch 7 psi ±2psi."

Also, in-tank lift pumps do not run at a very high pressure. 17 years ago my '02 received a replacement VP44 and an in-tank lift pump, all covered by warranty. The lift pump was the same in-tank lift pumps being used for early third generation common rail fuel systems. The lift pump operated at 6 psi (idle) and 3 psi (WOT). Normal. I drove with that lift pump for over 160,000 miles. At that time I changed to a frame mounted lift pump for ease of replacement - not for failure of the in-tank lift pump.

If I were in your shoes I would hook up a mechanical gauge and strap it to the driver side wiper arm. I would drive the truck and document the fuel pressure readings. This way you will know exactly what fuel pressures are for certain driving conditions.

I use a fuel pressure warning light for my VP44 injection fuel supply. However, I purchased an adjustable pressure switch (shown below). I did not set it at a specific pressure; I just kept lowering the pressure setting until I could drive the truck without the indicator lamp coming on, but the indicator lamp would come on with key on, engine not running. Although the pressure switch has only been installed for two month and 2,000 miles, it has been very reliable.

- John

 

[BERT E SHETLER]

Thanks for this.
These thoughts have crossed my mind, the possibility that I'm going through the struggle of replacing a perfectly good pump and that the dummy light is still going to glare at me, but at least I'll know the age of the lift pump. I'll cross these bridges when I come to them. Hopefully my shiny new pump will keep the light at bay for a while....

 

[Mhennessy]

The stock "filter pump" runs 6-8psi reg driving and WOT I would see 3-4psi. While you have your tank out you should consider the "vent mod" Glacier Diesel makes a kit but you could source the parts yourself.
The "mod" is moving your main vent to a higher spot on your tank and allowing 4-5 more gallons of fuel in your tank and quicker fill ups. (no clicking the tank pump handle a dozen times)

 

[BERT E SHETLER]

I must say, I'm happy to have done this job. I looked down into the pump enclosure today, and it's pretty grim down there.

 

[Ozymandias]

Yeah, seems the pre-owner sourced his fuel at mom&pops stations.

 

[Mhennessy]

She will appreciate getting the 18years of grim out of the tank.

 

[BERT E SHETLER]

Also, now I understand why, when I fill it up, the fuel gauge stays on Full for quite a while, then drops pretty fast. Seems like the float for the sender is pretty generic, spring loaded and all.
The tank is 14 1/2 inches deep, and the float only goes up to about 3/4 of a tank before it's straight up.
The more I work on her, the less mystery there is!

 

[sag2]

There is no pressure specification for the common rail trucks. The pump should flow at least one quart in 20 seconds. Check it after you have the tank clean and new pump installed.

 

[AH64ID]

Also, now I understand why, when I fill it up, the fuel gauge stays on Full for quite a while, then drops pretty fast. Seems like the float for the sender is pretty generic, spring loaded and all.
The tank is 14 1/2 inches deep, and the float only goes up to about 3/4 of a tank before it's straight up.
The more I work on her, the less mystery there is!

On a stock tank the module is compressed as it installs so the sender will be a little closer to the top, but not all the way up.

There is also programming that comes into play as the dash signal is modified by the ECM for the final gauge reading. I make it more linear in all of my custom tunes.

 

[Doc Holiday]

2004.5 4x4 6 speed manual
Hey everybody.
I've really learned a lot about this truck here, thanks to you guys.
This project:https://www.turbodieselregister.com/threads/preparing-for-a-pretty-big-trip.272221/ is what I'm dealing with now, but I wanted to start a new thread due to the fact that it all went down a road I didn't expect to be on.
I installed the PacBrake that was recommended, and it works as expected.
I decided against a rack of gauges that I potentially would have been wasting money upon.
Instead, I installed the BD Low fuel pressure warning light. Cheap and reliable.
I have found that the OE filter mounted lift pump has been replaced with the in-tank pump previous to my owning the truck.
So,,, after installing the alarm LED, I keyed up the pump a few times to purge the air, the light went out as expected. BUT what I didn't expect was that under normal driving conditions, driving around the neighborhood, the light comes on almost all the time. So this means I'm running under 5 psi fuel pressure all the time.

So, today I dropped the tank and ordered up a new in tank lift pump.
Now that the tank is out of the truck, I've found that there are 3 unused ports that are just open to the atmosphere. There aren't any other hoses connected, just the pressure line, the return line and the electrical connector. I intend to plug these before replacing the tank, but then I was wondering if I need a vent line?? No idea why these are there, or what they were for. Maybe it's a junkyard tank from a gas truck?
I will try to post a picture.
Any opinions and advice is welcome.
Cheers
Bert
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Those are in fact vents like the others said, you can put a rubber plug on them and it not hurt a thing. Mine have been plugged for almost 2 years now, the only difference between plugged and not is a whoosh of air when you take the fuel cap off.

 

[BigPapa]

you can put a rubber plug on them and it not hurt a thing. Mine have been plugged for almost 2 years now, the only difference between plugged and not is a whoosh of air when you take the fuel cap off.

The "whoosh" is because with the capped vents, no air is allowed into the tank as fuel goes out, creating a vacuum. This will reduce fuel flow as the vacuum gets stronger the same as a blockage. I would not suggest capping the vents off.

 

[Doc Holiday]

The "whoosh" is because with the capped vents, no air is allowed into the tank as fuel goes out, creating a vacuum. This will reduce fuel flow as the vacuum gets stronger the same as a blockage. I would not suggest capping the vents off.

Fuel supply has t been affected at all. I have an aftermarket pump and both a low and high pressure gauge. Also I never have and never will allow my fuel level below half a tank,

 

[AH64ID]

Agree, that’s not a best practice. It will cause premature fatigue for the pump, 1/2 tank or not.

Reminds me of the HPRV cap… that trend didn’t last long

 

[Doc Holiday]

Agree, that’s not a best practice. It will cause premature fatigue for the pump, 1/2 tank or not.

Reminds me of the HPRV cap… that trend didn’t last long

Lol well I have that done too…. Hope the boogeyman doesn’t get me.

 

[cerberusiam]

The blank gunk in the cannister is just a fact of life with a CR fuel system. The only way to limit the build up is run an additive package and\or run a specific additive for this problem, The black stuff is the same thing that turns the filter black, asphaltenes. It is basically tar cooked out of the fuel by the heat and pressures in the HPCR fuel system. Since the fuel return dumps back into the cannister the hot fuel is cooled there and the asphaltenes settle out and get sucked back into the LP. Filter does not catch them, the smaller ones end up in the cross over tube edge filters and the injectors, stock filtration is inadequate to catch them and the build up eventually cause fuel delivery issues and scoring in injectors. Another absolute positive effect of running a preventative additive package.

There in in fact a minimum pressure required for CP-3 operation, it is ~ 3 psi. Below that head pressure the CP-3 case pressure starts dropping and the COV begins prioritizing fuel to the rail and robbing the lube\cooling circuit. That is never good in HP pump that is lubed and cooled by fuel.

In addition, the lower the head pressure on the gear rotor pump the more cavitation occurs accelerating the wear on the gear rotor pump. The LP system wasn't really designed for long life based on proven hydraulic system experience. For optimal life expectancy the head pressure on any gear rotor pump should be in the 30% of target pressure, 16-20 psi at the CP-3 would be a well designed system.

 

[AH64ID]

When I spoke to Bosch many years ago they told me the minimum pressure was -5 psi for the CP3.