Gravity feed stock gas tank

[JMD]

My current EFI setup is using an inline fuel pump to draw from the stock pickup tube. It works okay, but once in awhile the pump loses prime and I know I’m going to burn the pump up if I don’t do something about it.
Rather than spend a ton of money on a fuel cell, I’d like to add an AN6 bung to the bottom of the stock tank. What’s the best way to go about this? Do I need to add a sump? Is there a spot on the tank that is ideal for adding a bung?

[americanmusc1e]

Just my two cents, but I highly suggest that you move to an in-tank fuel pump solution. Even if it's just rigging up a pump in the original tank. My first efi setup used an external GSL392 and I burned up two in 2 years.

My preferred solution would be an oem EFI tank because of the EFI sump. The 88 efi blazer tank is fairly inexpensive and works well on lwb trucks but doesn't fit well on swb trucks. Beware that if you are using more than a stock pump, the wiring in the factory sending unit/bulkhead won't take the additional amperage. http://67-72chevytrucks.com/vboard/s...82#post8770582


To answer your question. You can get a -6an bulkhead fitting that clamps on, but I doubt you'll be able to reach the nut on the backside to tighten it. And I wouldn't use something like that on a tank in the cab for fear of leaks.

You could also have a professional weld a 1/4" npt bung on the botton and then do a 1/4" npt to -6an adapter. WELDING ON A USED FUEL TANK IS EXTREMELY DANGEROUS. The tank needs to be thoroughly cleaned and than all oxygen/fumes inside the tank displaced with inert gas. Washing it out first is not enough. It's not a DIY operation.

[Ziegelsteinfaust]

If you pull out your pick up. You can cut the tube the sock is on, and splice in a in tank fuel pump. Like you would see on a new truck. The hole maybe to small on some in cab truck tanks.

If you must weld or braze on a used tank. Wash it out with dawn soap, and water. Then let dry. This usually works but can take a couple washings.

If you do not want to wash out the tank for reasons you may have. You have to purge the tank with nitrogen to remove fumes, and continue to purge as you weld. I have done this, but I have the equipment as course of my work. If you had to buy the purge regulator it costs roughly $150. Plus a bottle of nitrogen. Which is almost $300 if you do not already have one. Then you have to return it to get your core value back.

So purchasing a new tank solves a few other issues. Such as FI prefers being used with a bypass regulator. So the bypass sucks up all the debris in your tank, and the small rust particles can play hell with FI components.

If you have a in cab tank. It is a good time to step up to a blazer or suburban tank, and the pump components are much more bolt in. You will have to fab tank brackets.

So depending on what your playing with. You now have a few reasons to upgrade, and your wife called. She said it was ok.

[HO455]

Originally Posted by americanmusc1e

Just my two cents, but I highly suggest that you move to an in-tank fuel pump solution. Even if it's just rigging up a pump in the original tank. My first efi setup used an external GSL392 and I burned up two in 2 years.

My preferred solution would be an oem EFI tank because of the EFI sump. The 88 efi blazer tank is fairly inexpensive and works well on lwb trucks but doesn't fit well on swb trucks. Beware that if you are using more than a stock pump, the wiring in the factory sending unit/bulkhead won't take the additional amperage. http://67-72chevytrucks.com/vboard/s...82#post8770582


To answer your question. You can get a -6an bulkhead fitting that clamps on, but I doubt you'll be able to reach the nut on the backside to tighten it. And I wouldn't use something like that on a tank in the cab for fear of leaks.

You could also have a professional weld a 1/4" npt bung on the botton and then do a 1/4" npt to -6an adapter. WELDING ON A USED FUEL TANK IS EXTREMELY DANGEROUS. The tank needs to be thoroughly cleaned and than all oxygen/fumes inside the tank displaced with inert gas. Washing it out first is not enough. It's not a DIY operation.

I am assuming you are referring to a K5 Blazer and not an S10 Blazer tank? I know for a fact that 91 S10 Blazer tanks do not have any kind of sump in them.

[JMD]

Thanks for the suggestions guys, I had a feeling this wasn’t going to be cheap or easy...
Ideally I would install an under bed tank that’s already set up for EFI. However, my truck is a 4x4 shortbed with a small body lift, so a tank hanging below the frame is VERY visible and in my opinion it would look terrible.

I never really considered an in tank fuel pump in the stock tank. Wouldn’t that be horrendously loud? The pump I have mounted to the passenger side frame rail already annoys the crap out of me, so I would think having one right behind my head would be even worse. Has anyone had experience with this?

I planned to take my tank to a professional and get a fitting welded in for me. I just didn’t know if there were any reasons I shouldn’t go that route...

I’ve also been kicking around the idea of getting a diamond plate toolbox/fuel tank to mount in the bed. But they start at about $1000 and that’s just not going to happen.

[HO455]

It would depend on what you want the in tank pump to do. Is it going to give you the full 50-80 psi you need for the EFI or is it going to be just a low press high volume lift pump that supplies the EFI pressure pump?
For in tank only would suggest looking into a 90's vintage Lexus sc400 set up. The fuel tank is behind the back seat and the pump is not audible. They make 45 to 55 psi and are good for 325 hp. They are small diameter and should fit in our tank. And when your at the wrecking yard getting the pump get the fuel pump computer too. The computer will vary the pump speed to match the output pressure. So when the pump is pumping against maximum pressure in the line it will slow down to the minimum speed to maintain pressure at the volume needed and that does a lot to reduce pump noise.
Of if you go with the lift pump route find a suitable V8 car from the late 80's that has a 5-7 psi rating and use it to supply fuel to your existing pump. Then move your current pump forward in the truck away from the cab to reduce the noise.
What are you using for a pump currently?

[americanmusc1e]

Originally Posted by HO455

I am assuming you are referring to a K5 Blazer and not an S10 Blazer tank? I know for a fact that 91 S10 Blazer tanks do not have any kind of sump in them.

https://www.rockauto.com/en/moreinfo...61514&jsn=2261

late 80's K5 blazer

Great for a LWB, but they hang past the frame on a 67-72 swb. They are 25 gallons and they don't hang down near as far as the 67-72 blazer/burb tank. Here's a picture of mine before I cut the back of my frame down to swb. After I cut 6" off the back, the tank started looking like not something I wanted to get rear ended in.

[JMD]

I’m currently running a Holley 12-920 pump that was supplied with the Sniper EFI kit I purchased. It’s an 80gpm, 60psi pump. Can I run a low pressure (and therefore quieter) lift pump in the tank to supply the high pressure pump? My truck has a big block that should be pushing around 400hp, so I’m guessing a low pressure pump won’t provide enough volume to work properly.

[MARKDTN]

Originally Posted by HO455

....I know for a fact that 91 S10 Blazer tanks do not have any kind of sump in them.

Are you sure? Was yours a 4-cyl or 6? I did a TPI swap on a '72 SWB and I used an '86 (little) Blazer tank. It had a 2.8TBI in the Blazer. I just swapped to a TPI pump. I was pretty sure it had a sump. It fit pretty well but had to notch the frame a little to make it fit.

[americanmusc1e]

Originally Posted by JMD

I’m currently running a Holley 12-920 pump that was supplied with the Sniper EFI kit I purchased. It’s an 80gpm, 60psi pump. Can I run a low pressure (and therefore quieter) lift pump in the tank to supply the high pressure pump? My truck has a big block that should be pushing around 400hp, so I’m guessing a low pressure pump won’t provide enough volume to work properly.

A lift pump is a thought. Although modern in-tank units are very quiet compared to external units. put your head next to the fuel tank of any modern vehicle.


that Holley pump looks awful like a GSL392 that I had. They are noisier than the in-tank pumps. Those pumps also don't like to draw fuel. They only like to push it. I never tried a gravity feed, but I tried for a -8AN 1/2" feed to mine and it still started making death noises after a couple months of use.

[AussieinNC]

Not sure of your budget...but these alloy rear mount tanks come with the pump.

Being alloy, they are less prone to explosion due to sparks etc....

https://fueltankparts.com/collection...0-in-tank-pump

Work out all the items you need and maybe this would be a solution....

[TahoeK10]

you could also do something like this, and feed it with the stock mechanical pump.

https://fitechefi.com/product/force-fuel-system/

[HO455]

Originally Posted by MARKDTN

Are you sure? Was yours a 4-cyl or 6? I did a TPI swap on a '72 SWB and I used an '86 (little) Blazer tank. It had a 2.8TBI in the Blazer. I just swapped to a TPI pump. I was pretty sure it had a sump. It fit pretty well but had to notch the frame a little to make it fit.

Oh yes I'm sure. I had to replace the pump and sock on my 91 Blazer about 3 years ago and immediately I noticed that the truck would die while turning when the fuel tank was just above the 1/4 full mark. With the old pump it would run down to the last mark on the guage before it would starve for fuel.
So I dropped the tank and put a different sock on the pump. No difference. Then swapped pumps. No difference. I looked inside the tank with a mirror and found nothing. Both of the pumps I tried were Delphi units. So at this point I just never let the fuel get down to 1/4 full.
The point is I am sure the inside of the Blazer fuel tank has no sump. It is no different than the tank on my 67 Burban. It is quite possible that GM decided to do away with the sump in the years between yours and mine.

[JMD]

Originally Posted by TahoeK10

you could also do something like this, and feed it with the stock mechanical pump.

https://fitechefi.com/product/force-fuel-system/

That is a good option that I might end up going with if all else fails. I’m trying to avoid more clutter in the engine bay.

I have the opportunity to buy a used toolbox/auxiliary gas made by RDS Manufacturing.
http://www.rdsaluminum.com/auto-auxiliary.html
It has a 60 gal capacity, and is baffled. I believe I can add an aftermarket sending unit fairly easy. For now I would just use my current in-line pump until it fails, at which point I’ll add an in-tank pump. Thoughts?