What's the original configuration for your EEC (vapor canister) truck?

[71CHEVYSHORTBED402]

Having trouble confirming the original set-up for my 71, so I'll try this.

I'd like to reconnect the EEC to factory. The fuel sender has one 3/8" line that runs to the fuel pump. There's a 5/16" line, which is the vapor line. That's hooked up to a second port on the existing fuel pump, so I believe it just acts as a return line. That tells me, assuming the sender/tank are original, and I believe they are, that the original fuel pump had just one port (i.e., fuel source and no return line). Appreciate any corrections to that assumption.

There may and probably were some variances. There may also be an A/C factor, so I included it.

Thanks for chiming in.

[71CHEVYSHORTBED402]

Yeah, hardly nobody has it or really knows. I know a certain mod who does. ...................................Rumor is for an EEC, you're supposed to have three lines. Two from the sender, with one being a return, the other being for vapor.

However:
This is my 71 tank. Dollars to donuts it's all original. It looks to match-up to the illustration. I can't think of any configuration than a single port pump (no return line), with the 5/16" line for vent connecting to the canister.

Couldn't tell you what the line located at the top driver's side corner of the pic is for. I suspect it's for tank overflow.

[dfwright]

I posted on your earlier thread, My 72 has two lines from the sending unit, the output and return line. Then I have the vent line also. Three lines run from the cab to the front of the truck. The two gas lines to the fuel pump, and the vent line to the canister. Mine is a non-AC

[Shinysideup]

The fuel pump would be different between the EEC and No-EEC. Its more probable that things got changed over the years with these OLD trucks, than to believe they are pristine.

[71CHEVYSHORTBED402]

Originally Posted by dfwright

I posted on your earlier thread, My 72 has two lines from the sending unit, the output and return line. Then I have the vent line also. Three lines run from the cab to the front of the truck. The two gas lines to the fuel pump, and the vent line to the canister. Mine is a non-AC

Appreciate it. Yes, I've started too many threads on this. The sender on my 72 has two lines as well, but all evidence for EEC has been lifted, and even the tank differs. The top passenger corner of the tank doesn't have the vent line.

Hasn't been a complete loss by any means. In my research I located the PCV T part number, and snatched an NOS off Ebay for cheap. Also determined the part number for the correct gas cap.

Here's some good info..... http://what-when-how.com/automobile/...ems-automobile


"The first evaporative emission control (EEC) was introduced on 1970 cars due to California’s stringent emission law, and was used on all old and 1971 cars. "

"The fuel tank filler caps used on cars with EEC sys*tems differ from those used on cars without EEC systems. Most caps in EEC system are incorporated with built in pressure-vacuum relief (Fig. 17.20), so that a vacuum lock may develop due to the fuel expansion or contraction. It vents excess fuel tank pressure to the atmosphere in case the vapour delivery line is blocked. It allows fresh air to be drawn into the fuel tank to fill the space created by petrol as it is used.

"All EEC systems incorporate some type of liquid-vapour separator to prevent liquid fuel from reaching the engine crankcase or vapour storage canister. Some liquid-vapour separators are con*tained within the tank and use a single vapour vent line from the tank to the vapour canister. When the separator is not built into the tank (Fig. 17.21) it is usually installed on the outside of the tank or on the frame near it. In this case, vent lines extend from the tank to the separator and are arranged to vent the tank. Liquid fuel entering the separator returns to the tank through the shortest line. Okay, what's the liquid separator in our trucks?

This method of fuel vapour storage was introduced on all 1972 domestic cars in USA and since then is used on most cars in USA. The canister is placed under the hood (Fig. 17.21) and is filled with activated charcoal granules, which hold up to one-third their own weight in fuel vapours. The fuel tank is connected to the canister through a vent line. Carburettor fitted with external bowl vents are also vented to the canister."

An overfill limiter, or temperature expansion tank, was fitted on many 1970-73 EEC systems to limit total filling of the tank." Don't know if our tanks have this. /

[71CHEVYSHORTBED402]

A HA!............Just kidding. But really, someone chimed in with a single line sender on an EEC system. Single line port on the fuel pump right? Seriously, I don't know what else it could possibly be, but error on the side of caution, and I tend to overthink stuff that's new. Kind of a problem.

Any chance your truck is a 70-71?

[71CHEVYSHORTBED402]

Couldn't tell you why I didn't think of this before. Turns out all I had to do is look at the parts book. There are all types of fuel pumps. Should be noted my project truck is a 1971 C-10, 402/400 T.H...................My driver is a 1972 C-20, 402/400 T.H.

Fuel Pumps:

6470424 - 1971, all 400. Also works for all 68-70 trucks with a 396, and 1972 10-30 trucks without T.H. That's a single line pump.

6470779 - Mix of 71-72 trucks. Won't work for 71 T.H. That's a single line pump.

6470569 - 1972, 10-30, 350 with T.H. That's a duel line pump.

6470570 - 1972, 10-30, 400 with T.H. That's a duel line pump.

Go figure, this explains why my 72 400 T.H. is a dual line pump, and the 71 400 T.H. SHOULD BE a single line pump, like I thought it once was.

As if that wasn't enough verification, I moved onto fuel senders:

6428361 - 69-71, 10-30, with 4/BC, cab (350, 396, 400). That's a single line sender.

6429117 - 1972, Cab with A.T. (350, 400). That's a dual line sender.


I don't even see any EEC notations for these in the book. Nor are there references to A/C. At any rate..............I CAN PUT THIS TO REST, and comfortably select the first option in the OP. Thank you.