Fuel tank and vent questions - JeepForum.com
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post #1 of 8 Old 06-14-2021, 07:58 PM Thread Starter
Demaggg
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Fuel tank and vent questions

Hello and Happy Monday. Today I started the process of dropping the fuel tank on my 83 Renegade to replace the sending unit. The tank is MTS 21 gal replacement for a factory 15 gallon. There are 2 vent connections on the drivers side of the tank. The PO has them Teed together pretty much right at the tank and then into a hard line that runs almost to the fire wall and then rubber hose to the charcoal canister. I do not see any check valves along the way although I don't know where to look for them. My TSM it shows 2 vent lines Teed together right at the canister. Factory tank show a vent on each side. The MTS tank has 2 fittings an inch apart on one side. I wound of on my head years ago in an 84 I bought new so I want things to be as they should safety wise now that I'm an old fart. Is Teeing at the tank and one line forward ok? or is there a reason there there needs to be 2 lines all the way to the canister? Can the roll over check valve and liquid check valves still be purchased? The diagram in the TSM shows the first check valve with 2 inlets and one outlet but also shows 2 vent lined tied together at the canister? confused.


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post #2 of 8 Old 06-15-2021, 03:36 AM
keith460
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Two vent lines in the gas tank are actually extended internally inside. One for the left and one for the right side of the tank at opposite corners which allows venting when driving on slopes or leaning. The two lines tied together and just going to the Charcoal canister are completely bypassing the Liquid Check valve and Roll Over Check valve. There's no way to prevent fuel from making its way to the Charcoal Canister and contaminating it eventually. Your vent line would need to be high up and then come back down to meet the Charcoal Canister to be effective.


check-valve-routing-edited.jpg


And you won't find Liquid Check valves for sale unless used somewhere.

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post #3 of 8 Old 06-15-2021, 06:35 AM
Matt1981CJ7
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The MTS Company has replacement parts for the liquid and rollover check valves.

https://www.mtscompany.com/miscjeep.htm
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post #4 of 8 Old 06-15-2021, 07:23 AM
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https://genright.com/products/fuel-p...-and-cj-7.html

Turns that into a 15 minute job, never leaving your feet!
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post #5 of 8 Old 06-15-2021, 09:57 PM Thread Starter
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Thanks again to Keith460. Awesome pic of the vent system. I dropped the tank today and removed the sending unit or at least what was still attached to it. The float and arm had fallen off and were sitting at the bottom of the tank. I fished them out with a zip tie and thought great, this is why the fuel gauge always reads full. I had started hearing the float banging around in the tank a few days ago. After putting every thing back together I put 5 gallons of gas in the tank and fully expected to see a 1/4 tank there abouts, instead the the gauge went right to full.
I had calibrated the sending unit before putting it in with a meter (it was very close out of the box). I disconnected the lead at the sending unit and got 68 ohms. I then switched out the speedo cluster with a new Rugged Ridge unit that came with the Jeep when I bought it. Same thing, right to full. Tomorrow I'm going to ground the sending unit to the negative post of the battery. I'm also thinking of running a jumper from the sending unit wire right to the lug on the gauge. I did replumb the vent lines as high as I could get them up in the rear fender well and will install the unit MTS unit up there when they are back in stock. Thanks for the replies.
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post #6 of 8 Old 06-16-2021, 10:03 AM
John Strenk
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Quote:
Originally Posted by Demaggg View Post
Thanks again to Keith460. Awesome pic of the vent system. I dropped the tank today and removed the sending unit or at least what was still attached to it. The float and arm had fallen off and were sitting at the bottom of the tank. I fished them out with a zip tie and thought great, this is why the fuel gauge always reads full. I had started hearing the float banging around in the tank a few days ago. After putting every thing back together I put 5 gallons of gas in the tank and fully expected to see a 1/4 tank there abouts, instead the the gauge went right to full.
I had calibrated the sending unit before putting it in with a meter (it was very close out of the box). I disconnected the lead at the sending unit and got 68 ohms. I then switched out the speedo cluster with a new Rugged Ridge unit that came with the Jeep when I bought it. Same thing, right to full. Tomorrow I'm going to ground the sending unit to the negative post of the battery. I'm also thinking of running a jumper from the sending unit wire right to the lug on the gauge. I did replumb the vent lines as high as I could get them up in the rear fender well and will install the unit MTS unit up there when they are back in stock. Thanks for the replies.
Made doubly sure the speedometer is also grounded.

Usually a bad ground on the sending unit will just prevent the fuel gauge from moving.


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I drive a Prius to save money and buy more Jeep Parts....
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post #7 of 8 Old 06-16-2021, 01:32 PM Thread Starter
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Grounded the sending unit to the negative post of the battery and jumped the sending unit wire to the lug on the fuel gauge. I also tried grounding the body of the gauge to the negative post on the battery. Factory cluster acts the same way. Have the Rugged ridge unit in now as I'm afraid I'm going to fry the original cluster. Temp gauge works fine in both clusters.
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post #8 of 8 Old 06-16-2021, 08:42 PM Thread Starter
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Factory cluster back in. Filled the tank and the fuel needle moved way past full into the nether regions of the gauge. So it seems as if the gauge is kinda sorta working? I bench tested the sending unit be for installation and it seemed fine @ 75 ohms empty and 12 full. I have grounded the gauge from the housing to the battery to test but now its grounded to one of the 2 screws on the back of the gauge. It seems like the sending unit if off but I did test it. Any suggestions on a better way to ground the gauge? Could a poor ground cause this? Thinking of dropping tank and adjusting the sending unit on the fly to see if I can get the gauge into the proper zone. just got to burn off 20 gallons of gas. Dang.

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