Let's Talk about In-Cab Reproduction Gas Tanks and EEC vs non-EEC

[RustyPile]

Originally Posted by K10-Kansas

I have an EEC tank but I don't have 3 lines in the floor of the cab. I have 2. I have 1 fuel line and 1 vapor line. Does anyone know about these 3 lines?

I read through this old thread and most of the information is pure bologny and false, erroneous information.. The fuel pump has nothing to do with the EEC system. They are two totally separate systems not connected together in any way..

Starting at the fuel pump, there are 2 variations.. One pump has 2 connections - the rubber line coming from the sending unit in the tank, which is the pump suction line. This line draws fuel out of the tank. The other fitting (a flare type fitting) on the pump is connected to the line that delivers fuel to the carburetor. If you have only one line connection on the sending unit, this is probably the fuel delivery system you have.

The other fuel pump has 3 connections.. Two of the connections work as described above. The 3rd connection is a 1/4" nipple. it serves as a fuel return through a line back to the tank. This recirculation serves to keep fuel moving at a faster rate to help prevent vapor lock. This line runs basically parallel to the suction line all the way back to the tank sending unit.

The EEC system is a fuel vapor only system.. There is a nipple on the gas tank in the upper corner on the passenger side of the tank.. This nipple has a rubber hose connecting to a steel pipe that runs up through the B pillar and back down through the floor in the area where the liquid fuel lines pass through the floor. This line continues along the frame rail to the front and connects to the charcoal cannister located under the battery. Coming off the canister are 2 more vacuum lines connecting to vacuum control pieces on the engine.

The simple facts are:
#1- If you have 3 connections on the fuel pump and 2 on the sending unit, you have fuel recirculation plumbing..

#2- If you have that nipple on the upper passenger side of the tank, you have an EEC system. If the EEC system components are in place and working, you will need a non-vented gas cap for the system to properly function.

[71CHEVYSHORTBED402]

Originally Posted by RustyPile

I read through this old thread and most of the information is pure bologny and false, erroneous information.. The fuel pump has nothing to do with the EEC system. They are two totally separate systems not connected together in any way..

Starting at the fuel pump, there are 2 variations.. One pump has 2 connections - the rubber line coming from the sending unit in the tank, which is the pump suction line. This line draws fuel out of the tank. The other fitting (a flare type fitting) on the pump is connected to the line that delivers fuel to the carburetor. If you have only one line connection on the sending unit, this is probably the fuel delivery system you have.

The other fuel pump has 3 connections.. Two of the connections work as described above. The 3rd connection is a 1/4" nipple. it serves as a fuel return through a line back to the tank. This recirculation serves to keep fuel moving at a faster rate to help prevent vapor lock. This line runs basically parallel to the suction line all the way back to the tank sending unit.

The EEC system is a fuel vapor only system.. There is a nipple on the gas tank in the upper corner on the passenger side of the tank.. This nipple has a rubber hose connecting to a steel pipe that runs up through the B pillar and back down through the floor in the area where the liquid fuel lines pass through the floor. This line continues along the frame rail to the front and connects to the charcoal cannister located under the battery. Coming off the canister are 2 more vacuum lines connecting to vacuum control pieces on the engine.

The simple facts are:
#1- If you have 3 connections on the fuel pump and 2 on the sending unit, you have fuel recirculation plumbing..

#2- If you have that nipple on the upper passenger side of the tank, you have an EEC system. If the EEC system components are in place and working, you will need a non-vented gas cap for the system to properly function.

Good stuff.

If you go by the parts book the recirculated system was installed beginning in 1972ish. I say ish because you know, sometimes they installed new stuff before the next year, sometimes even old stuff from the former year.

You say it has nothing to do with one another, fuel/vapor. Tell that to my former mechanic After the canister and that were pulled he connected the vent line to where a return line would be on the fuel pump replacement. It worked somehow, couldn't tell you, though the replacement cap was vented.

You know what else is BS is vendors sell upper fuel lines varied on whether or not the truck has A/C. It has nothing to do with A/C, some people suggest it does. The difference is whether or not the fuel pump takes a return line. They figure a return line means it's A/C equipped

Here's a tank assembly for an EEC system for reference. Images of the two different fuel pumps too.

[RustyPile]

Originally Posted by 71CHEVYSHORTBED402

Good stuff.
<snip>...........You say it has nothing to do with one another, fuel/vapor. Tell that to my former mechanic After the canister and that were pulled he connected the vent line to where a return line would be on the fuel pump replacement. It worked somehow, couldn't tell you, though the replacement cap was vented...........<snip>

.

There is a difference between stupid and ignorant.. Ignorant is simply a lack of knowledge.. A little education and the problem is solved...

Now stupid is a horse of a different color.. Stupid can't, or won't, learn... They do things just because they can, not because they should. You'll have to tell that to your former mechanic yourself.. I never make any attempts to teach the stupid..

You are a wise man to have made him your "former mechanic"...

[71CHEVYSHORTBED402]

Originally Posted by RustyPile

There is a difference between stupid and ignorant.. Ignorant is simply a lack of knowledge.. A little education and the problem is solved...

Now stupid is a horse of a different color.. Stupid can't, or won't, learn... They do things just because they can, not because they should. You'll have to tell that to your former mechanic yourself.. I never make any attempts to teach the stupid..

You are a wise man to have made him your "former mechanic"...

Words of wisdom. Agree, personally I like being corrected and tuned. I'm world champion for questions, and too many times I think something is fact when it's not at all. It's an education when you're open to it, and hopefully learn to hold things at bay till proven.

He was actually a good mechanic for the most part. I think meth did him in. He took over the old man's shop, and that old man was excellent. I used them because I knew nothing about these and mechanical beyond simple, and shied away from it.

[RustyPile]

Originally Posted by 71CHEVYSHORTBED402

Words of wisdom. Agree, personally I like being corrected and tuned. I'm world champion for questions, and too many times I think something is fact when it's not at all. It's an education when you're open to it, and hopefully learn to hold things at bay till proven.

He was actually a good mechanic for the most part. I think meth did him in. He took over the old man's shop, and that old man was excellent. I used them because I knew nothing about these and mechanical beyond simple, and shied away from it.

'
I'm quite elderly and retired now, but I was a mechanic for some 30 plus years. Twelve of those years I was a shop owner. I would never do a hack job on any car in my shop or work space, even if the customer only wanted it done that way. I have ethics and a penchant for honesty. I had a good reputation and was rewarded very well for my efforts. I put both my kids through college. One is a loan officer at a lending institute and the other is a safety engineer at the worlds largest petroleum refinery.

[71CHEVYSHORTBED402]

Originally Posted by RustyPile

'
I'm quite elderly and retired now, but I was a mechanic for some 30 plus years. Twelve of those years I was a shop owner. I would never do a hack job on any car in my shop or work space, even if the customer only wanted it done that way. I have ethics and a penchant for honesty. I had a good reputation and was rewarded very well for my efforts. I put both my kids through college. One is a loan officer at a lending institute and the other is a safety engineer at the worlds largest petroleum refinery.

[RustyPile]

Originally Posted by 71CHEVYSHORTBED402

You don't realize just how fitting that photo/meme is to me.. Check the cover photo on my facebook page and you'll see why..

https://www.facebook.com/nick.gans.96

[Sheepdip]

Originally Posted by K10-Kansas

I have an EEC tank but I don't have 3 lines in the floor of the cab. I have 2. I have 1 fuel line and 1 vapor line. Does anyone know about these 3 lines?

I believe the third line was for an A/C truck and was a fuel pump by-pass return line to help prevent vapor lock.

[71CHEVYSHORTBED402]

Originally Posted by RustyPile

You don't realize just how fitting that photo/meme is to me.. Check the cover photo on my facebook page and you'll see why..

https://www.facebook.com/nick.gans.96

Irony is awesome. Same that farm, thank you. Texas must be neat, seems of the folks are handy and talented. I like how many can string words together & wit that comes with it. Nice B-day present, she must be a peach.

[71CHEVYSHORTBED402]

Originally Posted by Sheepdip

I believe the third line was for an A/C truck and was a fuel pump by-pass return line to help prevent vapor lock.

That's what I've heard, but I rebuilt this 71 a/c without it, because i'm 99% sure it didn't have a return. Hopefully it won't vapor lock, Gross

I believe this truck didn't have a return line because of memory, and how I found the truck when I tore her down. It's a numbers match original 402 A/C. I've had it since 89, the original owner was an old man who primarily left the truck alone.

A return line for example requires different tube retainer clips. This truck has them for 2 & 3 tubes where a return needs them for 3 & 4 tubes.

Additionally, if you look at the parts book, and if we're to assume it's correct and representing, the 71 took the shorter fuel pump (no return) and the single line fuel sender too. Regardless of A/C, it's straight forward.

If memory serves me right, the part's book calls for a return line for turbo hydramatic transmissions. Couldn't tell you why. Beginning in 1972. 71 takes a different fuel cap than 72 as well. Seems the 70 is the same as a 71.

[RustyPile]

Originally Posted by 71CHEVYSHORTBED402

Irony is awesome. Same that farm, thank you. Texas must be neat, seems of the folks are handy and talented. I like how many can string words together & wit that comes with it. Nice B-day present, she must be a peach.

Oh, she's a peach alright.. We met a little over 60 years ago when she was 14 and I was a college student. We celebrated our 56th wedding anniversary this past October.

[jnewt]

Originally Posted by K10-Kansas

I have an EEC tank but I don't have 3 lines in the floor of the cab. I have 2. I have 1 fuel line and 1 vapor line. Does anyone know about these 3 lines?

I believe the automatic trucks had three lines. Supply, return and the EEC vent. The manual trucks had two lines. Supply and EEC vent. Ive read somewhere the return line was to help with vapor lock issues.

[71CHEVYSHORTBED402]

Originally Posted by jnewt

I believe the automatic trucks had three lines. Supply, return and the EEC vent. The manual trucks had two lines. Supply and EEC vent. Ive read somewhere the return line was to help with vapor lock issues.

No

If we assume GM's parts book doesn't lie on the subject, and I don't believe it does in this case, return lines were installed beginning in 72, not to say late model 71 wouldn't have one. My 71 A/C 402/400TH didn't have a return line. The pick-up is one line and the pump the same. More confirmation is my retainers took no more than three lines (brakes, vapor, gas). Some of the retainers take four with a return.

But seems you're right about automatics, at least some. I know a 72 with a TH transmission calls for a return line. You may be right about vapor lock too, perhaps more prone with A/C on? My truck has never vapor locked, knock on wood.

[Canadian 72 C15]

Originally Posted by RustyPile

I read through this old thread and most of the information is pure bologny and false, erroneous information.. The fuel pump has nothing to do with the EEC system. They are two totally separate systems not connected together in any way..

Starting at the fuel pump, there are 2 variations.. One pump has 2 connections - the rubber line coming from the sending unit in the tank, which is the pump suction line. This line draws fuel out of the tank. The other fitting (a flare type fitting) on the pump is connected to the line that delivers fuel to the carburetor. If you have only one line connection on the sending unit, this is probably the fuel delivery system you have.

The other fuel pump has 3 connections.. Two of the connections work as described above. The 3rd connection is a 1/4" nipple. it serves as a fuel return through a line back to the tank. This recirculation serves to keep fuel moving at a faster rate to help prevent vapor lock. This line runs basically parallel to the suction line all the way back to the tank sending unit.

The EEC system is a fuel vapor only system.. There is a nipple on the gas tank in the upper corner on the passenger side of the tank.. This nipple has a rubber hose connecting to a steel pipe that runs up through the B pillar and back down through the floor in the area where the liquid fuel lines pass through the floor. This line continues along the frame rail to the front and connects to the charcoal cannister located under the battery. Coming off the canister are 2 more vacuum lines connecting to vacuum control pieces on the engine.

The simple facts are:
#1- If you have 3 connections on the fuel pump and 2 on the sending unit, you have fuel recirculation plumbing..

#2- If you have that nipple on the upper passenger side of the tank, you have an EEC system. If the EEC system components are in place and working, you will need a non-vented gas cap for the system to properly function.

Thanks for all of this info!! Just to clarify, if I have all of #2 but NOT all the components of the charcoal canister but just a line going to the front through the frame rail with a filter on the end to “cap” it off, then is a vented gas cap ok ?