This post is to help Chip (Low Elco) out in converting his atmospheric vented gas tank to an evaporative emissions control system (EEC) and the components that are needed to have an operative/functional EEC system. Others may find this post a benefit if they want to create an EEC system for their trucks but each individual is going to need to evaluate the system they have and how to incorporate all the components, it’s not hard to find or make the components but where to locate them on your truck can be the hard part.
First I’m going to start off with a safety warning (I know ugggg), but thesis are problems that I’ve run into and seen others have. All the hoses that are in contact with gas or fuel vapors should be able to handle fuel. There are plenty of hoses out there that are made for other things like water or vacuum that are not suitable for handling fuel, they have a good chance of failure over time. I’ve had the parts man try to give me a 5/8 water hose when I wanted a 5/8 fuel vent hose, the hose should be marked for fuel/gas or petroleum.
I always like to see what the factory used to create their EEC system and incorporate their components in my system in some manner. This does not mean that you have to buy specific factory items for a specific year, but in fact you can make some of them rather than trying to find some that the factory used. I will be including some marked up pictures that may be of benefit for understanding and referencing back in my build thread to what I did.
Let’s start with the fuel tank. Not all fuel tanks can be used to make an EEC system, they have to have some other way to vent the fuel tank other than the filler cap. If you have a fuel tank behind the seat that’s vented thru the cap you will probably have to change the fuel tank to incorporate an EEC system. Here are two pictures below that show the differences in factory tanks that can go behind the seat.
Now a common modification is to relocate the fuel tank under the bed. I did this with a blazer style fuel tank and if you look back thru this build thread you can find some pictures of what I did (ref post #301
http://67-72chevytrucks.com/vboard/s...318544&page=13 ). Chip is using a 1990 Jeep wrangler tank and it has vents other than just thru the gas cap. There are a number of different fuel tanks that can be fitted under the bed and each one may have certain problems in making them fit and function. This post is not trying to address how to install the tank or what tank to use but how to fit an EEC system on one. Again here are some pictures showing what the different factories (Blazer and Jeep) did to create an EEC system.
Chip sent me some pictures of his fuel tank and I’m going to try to identify the vent lines and mark them on the pictures. You need to look at the fuel tank that your using and identify all the lines and what to use them for, we don’t want to hook up the wrong lines.
As you can see in the above picture Chip has many fuel lines on his tank, you will probably have less. You need to look at the tank you have and identify all the lines and determine what ones you are going to use, or cap off. As a minimum you will need three lines on your tank to create an EEC system, Filler tube/Cap, Fuel Feed Line, and Fuel Vent Line. In the above picture I was unable to point to the exact fuel hoses that come out of the fuel sending unit (there are four) as to what each hose hooks up to because the picture is just at the wrong angle to see, but I did point/mark the lines from the bottom of the sending unit. Let look at each hose and figure out what they do and if you’re going to be using them.
1 (Fuel filler vent tube/hose) Just because this hose says vent on some diagrams does not mean that it vents the tank all the time. Its primary purpose is to vent back into the filler tube, so that air can escape from the fuel tank when you’re filling the tank with gas. Generally it’s a hose size of 5/8 to ¾ inch in dia. and you need to use it or you could run into problems in filling the gas tank (very slow filling). Is the hose your using fuel safe, if your parts store can’t supply you with one try NAPA they can get you the larger size fuel hoses.
2 (Fuel filler tube/Cap) From 1973 and newer all gas caps for cars/light trucks are not vented to the atmosphere and you need a non-vented gas cap to create an EEC system. You may find some gas caps that say that there pressure/ vacuum caps, this is a safety feature only and will meet your needs in creating an EEC system. They only relieve pressure/vacuum under extreme conditions if the other vents become inoperative.
3 (Fuel feed/pick up tube) Yes you need this one, this hose goes to your fuel pump to feed your engine (didn’t want to skip a line for total understanding ---- smile). Normally this is about a 3/8 tube/hose, it has to be big enough to supply adequate fuel to the engine.
3 (Fuel return line) This line is for a fuel return that is generally needed for fuel injected engines, Chip’s is not a fuel injected engine and I would cap this line off. The size of this line is about the same size as the fuel line feeding the engine.
4 (fuel vent line on the sending unit) It’s not visible from the bottom of the sending unit but this is the fourth line coming out of the top of the sending unit. The tube/hose size is generally smaller than the fuel feed line but not always. If this was the only vent line on this tank I would use it for the EEC system, but Chip has two other vent lines on his tank (just to simplify the vent line hose runs I would cap this line off at the sending unit, it could be tied into the other vent lines if desired).
5 (2 EEC vent tubes/hoses on the right side of the fuel tank) I would use both of them to create the EEC system. The size of the tubes/hoses are 3/8 or smaller.
For the lines that you decide to cap off I use a safe and simple method. I get a fuel capable hose the size of the tube I want to cap off (about 3 to 4 inches long), two hose clamps, and a steel or aluminum peace of rod the right size for the inside of the hose ( approximately 1 inch long). Slip the hose on the tube insert the rod in the other end clamp both ends and you have a very safe and effective cap. Caps like the ones you could find on the carburetor for capping off vacuum lines are not suitable, they can leak, fall off, or deteriorate. I’ve seen others try to use them, (be safe around fuel components).
Continued in next post