Fuel tank install - without the old one as a guide... - JeepForum.com
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post #1 of 20 Old 09-20-2021, 05:06 PM Thread Starter
Islander13
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Fuel tank install - without the old one as a guide...

I could use a little guidance here. My new to me '81 CJ7 came without an installed fuel tank. There was one bolted in that the previous said he bought used but wasn't the right one.

So I've ordered a replacement Spectra and an Omni-Ada sending unit. Without taking out the old one, I have to figure out where to connect the lines. I have to wait at least a few days for the new tank/sending unit, so just doing some advance research. I've seen tank removal videos, but not straight up installs. So I'm assuming that:

the the fuel lines connect to the sending unit via fuel safe lines rubber lines that I'll have to pick up.

The vent lines connect directly to the vent side of the tank

The fuel fill and vent hoses connect directly to the tank

I think that's straight forward, but I was confused seeing the old tank with fuel lines that connected in a 'Y' fitting.

Any advice is appreciated.

I should note hat the undercarriage is in good shape. I did run my borescope up the fuel fill lines and they looked good. I can't fit the scope up the metal fuel lines to the pump.

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post #2 of 20 Old 09-21-2021, 07:17 PM
JEEPFELLER
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Maybe this is start for you

Others will probably help out too

This is what a '81 tank looks like

https://www.carparts.com/details/Jee...E&gclsrc=aw.ds

This is a diagram for a '77 from the factory service manual. The filler end has the correct kinda parts, it may be configured a a bit different on an '81 (routed different--I'm not sure)-------the vent end is the same from '76-'86 (you can see what is missing on yours) Maybe someone has the '81 diagram for you.

-----JEEPFELLER
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post #3 of 20 Old 09-21-2021, 07:56 PM Thread Starter
Islander13
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Thanks Jeepster. I love the schematic. This '77 diagram only has one fuel line forward to the pump.
My sending unit has two connections as well as the electrical. I also have 2 metal fuel lines going forward. I read somewhere that the extra line is a return line that they added for emissions.
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post #4 of 20 Old 09-21-2021, 08:11 PM
Girth83
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Here's a pic of the tank/lines from my 1982 TSM. Bit different layout than the '81 tank it looks like, judging by the link JEEPFELLER posted, but some of the same features maybe?
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Last edited by Girth83; 09-21-2021 at 08:43 PM.
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post #5 of 20 Old 09-21-2021, 08:31 PM
JEEPFELLER
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Girth83 repost the diagram, it did not show.

The return serves 2 purposes I know of.

To keep from over pressuring the needle and seat inside the carb

and

To keep fuel moving---this prevent the fuel from staying in one place and being overheated by exhaust related parts---this would possibly cause "Vapor Lock" and keep fuel from reaching the carb.

Pic of what the other end looks like----the regulator and gauge are addons on my Jeep. Pic 1 was used explain elsewhere.

Pic 2- that's the return line connected to the down side of my regulator. (this configuration works the best to control pressure to the carb)(believe it or not)

Insure you don't switch the suction line (connected to the long tube and screen) with the return (sorta dumps back in from up higher)

-----JEEPFELLER
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post #6 of 20 Old 09-22-2021, 02:29 AM
BagusJeep
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The electrical connection was to the fuel gauge sender. It is a single wire (pink if I recall). To get better readings you can install a black wire of the same size to the metal structure of the sender unit and run it all the way back to the instrument cluster holding down bolt.

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post #7 of 20 Old 09-22-2021, 10:11 AM
John Strenk
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Yes, pink is for the fuel. And the other one is a ground connection.

I guess you couldn't trust the sending unit to maintain a good ground connection.


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post #8 of 20 Old 09-22-2021, 12:51 PM Thread Starter
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Thanks to all. I realized last night after looking at the old tank again that the merged lines in the 'Y' in the one pic are actually the vent lines not the fuel supply and return lines. That was confusing me.
I did follow the lines off the fuel filter and one goes to the carb and one does return back to the tank.
So I should have everything I need except for some fuel safe 5/16" and 1/4" rubber lines to connect from the metal lines to the sending unit.
Because I didn't take the old tank out, I'll have to re-source the bolts to attach the skid plate/tank to the chassis. The new tank and sending unit should be here within a week. The old pan/skid plate is in good shape so I will reuse it after a good wire brushing and some POR15. I have ordered new straps though.

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post #9 of 20 Old 09-22-2021, 11:12 PM
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The bolts which hold my skid plate / tank cradle on are coach bolts. The square end under the head allows them to sit in the square holes in the body and hence do not turn when you offer up the tank and put on the nuts. Very thoughtful of AMC to put them on, it is one of the few things about the whole drop tank thing that is made easier.
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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
1980 Land Rover Series III 109" troop carrier - ROVER
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post #10 of 20 Old 09-23-2021, 05:34 AM
keith460
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I tried to upload photos yesterday from my hotel but bandwidth too slow I guess.

Try again....

fuel-tank-skid-8-.jpg

fuel-tank-skid-7-.jpg

fuel-tank-skid-21-.jpg

fuel-tank-skid-26-.jpg

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post #11 of 20 Old 09-23-2021, 05:39 AM
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And some more.


img_6146.jpg

img_6159.jpg

img_6177.jpg

check-valve-routing.jpg

check-valve-routing-edited.jpg

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post #12 of 20 Old 09-23-2021, 08:01 AM
Ken4444
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Quote:
Originally Posted by keith460 View Post
And some more..
Keith, when you took all of the photos of your build years ago, did you have any idea you'd be re-posting them regularly in order to help people?

"I give you a republic, if you can keep it." - Benjamin Franklin
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post #13 of 20 Old 09-23-2021, 08:46 AM
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Great Photos Keith!

I thought of another bit of help that the OP may need and maybe John Strenk can chime in on. Before you get the tank back in completely, you may want to calibrate the fuel gauge so it accurately depicts the amount in the tank. I’m unsure if there is an adjustment on your year model or not, but I remember difficulties with this when my my in-tank sensor was replaced some +20 years ago.
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post #14 of 20 Old 09-23-2021, 12:34 PM
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Quote:
Originally Posted by Ken4444 View Post
Keith, when you took all of the photos of your build years ago, did you have any idea you'd be re-posting them regularly in order to help people?

Yes I did. Most JF members don't know how or use the search feature and results don't always give you what you want without reading through many post. Key Words are really the only way to narrow down the search to find a specific item one needs info on.

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post #15 of 20 Old 09-23-2021, 01:31 PM Thread Starter
Islander13
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wow... Thanks Keith. Those pics are great. Without pulling the tank out - there were a couple of mysteries. You pretty much cleared most of them up with those pics. Thanks!

Ken D
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