Fuel tank in place where the spare tire is located.

[87carl]

I know this is an old thread but instead of making a new thread on this topic I figured bring this one back from the dead. I have been wanting to do this since the day I bought my burb. Has anyone done this yet?
I was thinking of getting a 42 gallon tank and the rear crossmembers that the tank straps mount to from a older burb 90s era obs. Then cut my spare tire mount out and burn in some mounts for the obs burb tank and use a filler neck from the obs burb in my stock fill neck spot. would also have to extend fuel pump wires and hoses. This is another mod high on my priority list I hate the small 20 gallon tank that is slow to fill and constantly clicking off early.
Only question I have is will the obs burb sending unit work with the 07 electronics? And how do I figure out how to plumb the evap hoses

 

[87carl]

So I was thinking about this some more and said **** it and went and took some measure ments.

So between the frame rails is just over 36".

From the rear bumper to the next cross brace going forward that has body mounts on it that I wouldn't want to spend the time modifying is a little over 30".

And from the lowest point on the body to the bottom of the factory rear bumper cover is 10".

So just using those measurements you have a volume of over 46 gallons.

View attachment 201977

Excuse my dirty truck but you can see there is quite a bit of room there. You would need to remove the 2 vertical support beams that connect with the plate that goes across the top of the frame. Then you can just add another channel support near the rear bumper.

And the tank could be taller than 10", closer to the middle of the truck since the body raises up a little bit and it can hang lower since you wouldn't have to worry about it getting hit on anything.

So According to these measurements we can have a tank is that 30 length x36 width and a little over ten inches tall
29.75 width x 33.5 length x 13.13 in. Is the dimensions of a 98-99 42 gallon tank so that sounds like it will be tight but should fit if turned 90 degrees which would mean building custom mounts for the tank straps on the frame rails (easy). If I turn it so fill neck inlet is in front drivers side corner of the tank and use a small piece of filler hose and connect that to a elbow pointing at filler neck and a second hose to connect elbow to neck that should be easy to do the smaller hose on filler neck is flexible enough to connect to the barn on the top of the tank.
The 2007 fuel pumps I think have a bigger diameter and won't fit so I would use the obs pump sending unit.

Just would have to figure out all the hose routing and wiring to know how to connect everything and gotta figure out how to connect to the old fuel and evap hoses to extend them. does anyone have any ideas or info that could help me figure out how to do that?

 

[Bill 1960]

@87carl is the new tank just going to gravity flow into the original, or are you thinking a switching valve? If they’re gravity tied together I would think a single evap connection to whichever tank is higher would work.

Or are you eliminating the original tank?

 

[87carl]

@87carl is the new tank just going to gravity flow into the original, or are you thinking a switching valve? If they’re gravity tied together I would think a single evap connection to whichever tank is higher would work.

Or are you eliminating the original tank?

Eliminating original tank

 

[87carl]

Just measured my burb there's enough room for the tank to go either direction. got wife ok with ordering a 98-99 tank and all the pieces to my burbs stock evap system and obs 98-99 tank vent valves and pump. Should be able to do it around 500 bucks. Will replace all evap lines with rubber hose it's got a evap code I am hoping to eliminate while doing this. Does anyone know what size hoses I will need to do it. debating on if I will need to put a new rear crossmember in to strengthen rear frame after removing spare tire mount. Maybe cut something out of a parts car I've got few junkers sitting around thinking maybe 36 inches of a late 90s truck frame section out from under where cab was would work great and give a spot to mount straps if I run tank without turning it. I got a 97 tahoe filler neck somewhere round here I can use but I think I might be able to keep 07 filler neck it comes out in a good spot for the obs tank. Figure If gonna do it might as well do it now while burb is in middle of a mild rebuild and ain't being driven. Plus she is due for her annual inspection end of month and the evap is one of things preventing her from passing. And she goes for her annual undercoating beginning of April so anything getting modified is best to do now so it can get coated.

 

[992dr]

Could you modify the OBS tank to fit the NNBS pump?
I'd guess you could get all new lines made to the desired length so it would end up being a drop in assembly.
Please take lots of pictures and write down all the dimensions

 

[Rocket Man]

Could you modify the OBS tank to fit the NNBS pump?
I'd guess you could get all new lines made to the desired length so it would end up being a drop in assembly.
Please take lots of pictures and write down all the dimensions

Pretty sure he’s gonna have to. The FPR, filter, sending unit and pump are all one unit in the tank on a NNBS plus the wiring system is completely different.

 

[992dr]

Pretty sure he’s gonna have to. The FPR, filter, sending unit and pump are all one unit in the tank on a NNBS plus the wiring system is completely different.

That's what I was thinking.
I thought he had mentioned something about using the OBS pump

 

[87carl]

Could you modify the OBS tank to fit the NNBS pump?
I'd guess you could get all new lines made to the desired length so it would end up being a drop in assembly.
Please take lots of pictures and write down all the dimensions

Pretty sure he’s gonna have to. The FPR, filter, sending unit and pump are all one unit in the tank on a NNBS plus the wiring system is completely different.

That's what I was thinking.
I thought he had mentioned something about using the OBS pump

I am planning on using the obs pump. The 1998 fuel pump lock ring is
Inside Diameter 111.0 MM
Outside Diameter 122.0 mm
2007 it is
Inside Diameter 124.6 MM
Outside Diameter 187MM
And they are completely different designs so to get the 2007 pump to work in the 98 tank would be a challenge.
When I extend fuel lines I will put a fuel filter in line. I didn't know anything about the new pumps having a built in pressure regulator? Do you know what psi they regulate pressure to? If needed I can get a fuel pressure regulator and plumb it in.
What is different about the 07 pumps electrical system? Both pumps have 3 wires going to the tank pressure sensor on top and both 98 and 07 use same part number for pressure sensor. both pumps have 2 wires to the pump and 2 wires to fuel level. I do gotta figure out a way to test the voltage sweep range on fuel level to see if they match but I'm betting they're the same.
Idk how or where you can order custom extended fuel lines like stock lines. if I can find an adapter to plug into the old fuel lines where they connected to stock tank I will use that to run rubber hose to new tank I know they make those adapters I've used them on other projects but I can't think what to search for to find them or can run rubber hose all the way to engine if I have to. And will use rubber hose to replace all evap lines.

 

[87carl]

From what I can find the nnbs have a fuel injection pressure sensor in the fuel line just infront of the abs module. And that send signals to the fuel pump control module to regulate fuel pressure. Not a actual pressure regulator in the sending unit so that should be fine with the obs pump