Body - Fuel line and vapor line routing question (2024)

Here are two great videos showing both the supply and return line routing on a CJ with the body off at the time.

Youtube Video 1

Youtube Video 2

Note: Added video embed. -- CJ

I dropped the tank this morning.

I learned today that this jeep sat for a very long period of time. I siphoned the fuel out of the tank and got 10 gallons of gasoline, sludge, and varnish. It is one of the nastiest fuel tanks I've ever seen. The siphon tube went BLACK when I scraped the bottom of the tank with it. I also found remnants of the last sending tube/tank sock, roughly a handful of rusty debris, some loose nuts/bolts and the float. The sending unit is completely roached.

I have a bunch of questions.

Did all CJ7s come with a plastic tank?

I'm happy that mine has one but I don't if it's original nor do I know the capacity. The skidplate holding it up is a diamond plate home fab job and none of it looks factory to me. There are several choices for sending unit tube length on rockauto and I don't know which one to pick. Can someone recommend a good stock replacement for the sending unit? I'll try and scrape some part numbers off the tank.

I vacuumed all the chunks and debris out of it but there is still a layer of filth/grime on the inside. I'm thinking about hitting it with an RV sewer tank wand (sounds gross but it's not) and rinsing with diesel. Is there an easier/better way?

After watching the videos above, I have a few questions about the fuel system. There are three lines to the tank. One that sends fuel to the fuel pump, another return line from the top fuel filter port. A second line connects the two RCVs to the charcoal canister. What does the other side of the canister go to? I don't have a charcoal canister - it was removed by a PO along with all of the emissions and vacuum lines. I have no intention of restoring the emissions. I'm looking for a solution where it runs good and doesn't suffocate me with noxious fumes sitting at a red light in traffic. What do I need, fuel-system wise, in order to accomplish that and seal the two holes in the top of the tank where the RCVs were? The RCVs both need replacing. The rubber grommets that hold them in place disintegrated into a black RTV-like substance that I cannot get off my hands no matter how much I scrub. The rubber lines and clamps attached to them look to be from 1985. Do I need these things at all given my goals? Can I just cap the holes with something?

Thanks in advance. You guys have been super helpful!!

The original tank would normally have been steel. A poly or plastic tank is after market. The original tank would have been 15 gallons in most cases, although a 20 gallon option was available. I believe some 20 gallon OEM tanks were plastic. As an after market option, you can get a 20 gallon tank that fits in place of the original 15 gallon and requires a lengthened skid plate. And obviously the 20 gallon also needs a different sending unit/pickup tube. The 20 gallon EOM tanks have two ports on the top (to the sides) and the location of the sender unit is different. Here's a shot of a 20 gallon OEM next to a 15 gallon.

Those two lines on the driver side of the tank are for venting and go through the liquid and rollover check valves and charcoal canister as you have stated. Here is a diagram showing those connections.

While partially for emissions (capturing fumes from the tank venting), that is really a safety feature in case of a roll over to keep fuel from running out of the tank. In terms of the canister, you see one line goes to the charcoal canister up under the hood. The other ports on the canister go to the carb, a PCV "tee" connector, etc. This is to vent the gas tank and also capture those gas fumes to be burnt in the engine. Here's a diagram of that.

When I switched to fuel injection, I moved my canister from under the hood to inside the rear fender well on the driver side (needed the space under the hood for the larger engine and other stuff). I have the check valves and the canister mounted together. I have the one connection from the rollover check valve to the canister (labeled "fuel tank vent" in the pic) and from the canister to a ported vacuum source on my throttle body (labeled "additional ported vacuum source" in the pic). I capped off the canister connections for the PCV valve "tee" and the carb bowl vent. Now my tank is still vented, my rollover and liquid check valves are still there just in case, and I have no issue of fuel fumes or smell. NOTE: I have the original 15 gallon steel tank.

Looks like I have an OEM 20 gallon plastic tank. I got the part number off it and looked it up. It looks exactly like the first picture you posted. I ordered a sending unit that I hope will work. Crown part number ‎5362090K. It at least comes with the large black plastic hex locking ring so I hope it's the right one.

Do I NEED to have a charcoal canister? If I don't, then I don't need the RCVs either. I will just plug the holes in the tank (which should then be fine in case of a rollover.)

I still want to understand what I need to replace to get it running right. Are the RCVs and charcoal canister necessary or not?

The RCVs and the charcoal canister are NOT needed to just get it running. But with no vent connections, you could get vapor lock issues. So without any venting connections, you should consider a vented gas cap; if you live in an area where that will pass inspection.

The sending unit you ordered is the right one. Just beware of the plastic float as they develop leaks in short order. You can get a brass one that fits right in and will survive longer. Here's the one I got: Amazon link

Also Crown units are iffy. These have been known to not read accurately and have frequent failures. I'm not trying to be a "negative nellie", just trying to help from my prior experience and that of others. Vphix and Spectra make a great unit.

Give these guys a looksee. It's the one I use.

https://www.spectrapremium.com/en/aftermarket/north-america/classic-sending-unit

Project86 said:

Give these guys a looksee. It's the one I use.

https://www.spectrapremium.com/en/aftermarket/north-america/classic-sending-unit

Click to expand...

They don't seem to have a sending unit for a 1985 / Jeep / CJ7 / Base L6 4.2L sending unit for a 20 gallon tank.

4.2 sending unit CJ7 20 gal

The sending unit I ordered arrived today and it's too short. Since I already have it, I'm going to cut the tube and extend it with a piece of fuel line and a couple of stainless steel clamps.

Since I don't have a canister and don't plan to run one, I don't need the rollover check valves. I searched high and low and I couldn't find anyone that sold a plug to fill the hole, only talk about which RCV to buy. Enter the 3d printer. I printed two of these plugs. I'll run RTV around the rim and drop them into the holes in the top of the tank left by the RCVs. I have the other of these two plugs soaking in gas overnight to make sure they don't dissolve but this should solve my RCV problem.

I'll adjust the length of the sending unit, replace the fuel and vapor lines and all the rubber lines, and use a vented gas cap.

I also have a carb rebuild kit on my to-do list. My question is what to do with the carb bowl vent? Right now it's plugged completely (assuming I'm identifying it correctly). Do I need this? Should I tee it into the vapor line from the fuel filter?

15 gal sending unit

AndyCJ7 said:

The sending unit I ordered arrived today and it's too short. Since I already have it, I'm going to cut the tube and extend it with a piece of fuel line and a couple of stainless steel clamps.

I also have a carb rebuild kit on my to-do list. My question is what to do with the carb bowl vent? Right now it's plugged completely (assuming I'm identifying it correctly). Do I need this? Should I tee it into the vapor line from the fuel filter?

Click to expand...

Extending the pickup tube on your sending unit as you described should work just fine. I did this for my fuel injection setup to mount an electric pump inside the tank.

As for the carb bowl vent, leave it plugged since you aren't venting the tank back to the carb via a charcoal canister. That third connection on the fuel filter is for the return line to the tank, not a vent.

A PO had a heater core leak and "bypassed" it. By this I mean that the coolant line from the rear of the intake manifold was capped off, along withe corresponding line from the water pump to the heater core.. I have to believe that one of the contributing factors to the vapor lock issue on this jeep is the fact that coolant could not flow through the intake manifold. I'm fine with bypassing the heater (I live in SW FL) but I really think that the intake manifold not getting any coolant flow was a contributing factor to this jeep dying and refusing to start after 15-20 minutes of driving.

I think what happened here is the 2nd-previous owner (or earlier) stripped the emissions stuff off and created the vapor lock issue. He had no money and no skills to figure it out so he sold it. The previous owner (to me) bought it, had no idea what was wrong with it, who then sold it to me for cheap because he couldn't even fix the brakes on it, never mind anything else that it needed. It wouldn't even idle without my foot on the gas when I got it. When I pulled the rear passenger drum off, all the brake hardware fell out onto the garage floor.

I have a new water pump, thermostat and coolant hoses on the way. I will bypass the heater core properly and hopefully keep the intake a lot cooler too.

Once I get the fuel system straightened out, the cooling system rebuilt, and the power steering mounted properly I'll be ready to tackle the wiring mess. Now that I have the radiator out, I can see the wiring for the headlights, marker lights, etc. and there's a lot of electrical tape and other signs of shoddy looking wiring. I'm sure the rest of it is no better.

After I get all this straightened out, I'll have a pretty decent jeep!