70 Mach I fuel line question


Jan 26, 2006
Nashville, TN
I am still in the process of this 70 Mach I, 351 4V. It has two lines at the gas tank, one goes to the fuel pump, the other goes to the engine compartment somewhere, it is cut off at the fire wall. There is also a valve or something on the left frame next to the gas tank which I don't have a clue what it is, I've worked on mustangs when I was younger and never run across this plastic (valve) ???? It had one hose connected to it and looks like the other side is broke off, it was cover with a tin casing. I have looked in the parts catalogs and haven't found anything that looks like it. Maybe it was an aftermarket part but it doesn't look like it is, there is a number 237 9 1 on it.

Any help would be greatly appreciated.

Oh, is the front wiring harness (from the firewall up) the same for a 70 as it is a 69, I have to find one as the body shop lost mine (go figure) My car also has the built in tach.

Thanks in advance,
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My 351C 4V 70 Mach1 never had two fuel lines.

My fuel line ran up the driver's side rear frame rail, then out next to the rocker, then back in near the front subframe, through the holes in the torque box, into the front fender well, then up and over the front frame horn and into the engine compartment.

I've never heard of a carbureted vehicle with a fuel return line.

Is it possible your car is a california model that perhaps had a charcoal canister all the way back in '70? I thought those didn't come in until the mid seventies about the same time the catalytic converters went on.
Very wierd... I dunno where my 70 was destined to be sold but it could be seeing i live in CA and the previous two owners were here too. Then again it is a Q code so I don't know what fuel differences it entails with the unique 735cfm carb and all.
There should be a 4" or so rubber hose from the tank sending unit to a hard line. That hard line will run down the drivers rear frame rail and under the drivers floor pan next to the rocker lip. It will terminate before the rear of the drivers torque box, where another 6" rubber fuel connecting that line with the front hard line. The front hard line starts on the drivers outside front frame rail just in front of the torque box, runs along the frame rail, and enters the engine bay through the front fender apron (in front of the shock tower). From there a rubber hose will run from that hard line to the fuel pump. Then a hard line will run from the fuel pump to the carberator. This is the same for all 70 cars. Only a pic of the plastic thing will help us determine what it is.

Oh and ALL 69 main harnesses are different. Front headlight harness is different due to the additional headlights and different side marker lights, underdash harness is different due to ignition switch difference (among many), and taillight harness is different due to taillight differences IIRC. Hope this helps!
The fuel lines seem factory, same clamps, etc. I understand the fuel line to the fuel pump, the other ran on the other side through the tunnel. There is a vaccuum cannister that goes somewhere (the person restoring my car quit after tearing everything down, then gave it back to me in boxes) That's why I'm having some problems, otherwise I would have had photos before I removed anything.

I'll try to get a picture on here of the valve, it sure looks factory!
I'm betting this has to be some early emissions stuff that was california only, I bet it's for evaporative emissions, charcoal canister, etc, which means that second line was a "vapor" line, not a return line.
automart said:
Thanks guys for the info! It does have a cannister under the rf fender with the hose attatchment going through to the engine compartment.

Thats your vacuum can for A/C. Does the gas tank have some plastic pieces attached to it inside the trunk on the drivers side? that is where all the cali emissions stuff was at on our cars.

I just read your post about the fuel line on your mach 1. I assume you have that fugured out by now. I have a question out there now about how the fuel line runs around the rear whell well. Any way you could take a pic for me? Thanks
Your car is prob like mine which has the same 2nd line on it. My car is def. a Calif. car and it ans some other 70 Mustangs had a first generation EVAP system on them. The 2nd line your talking about ran to a Vapor canister which mounted to the frame just infront ot the RH Lower Control Arm then another aprox 1" dia. corigated paper Vapor hose ran up to the side of the Air Cleaner. If you would like to discuss in detail Please feel free to e-mail me at [email protected] I would like to talk to you about your 70 car.
Check your fuel tank. If it is still original, and came with the evaporative emissions package, it has a different tank that's 20 gallon, instead of 22. It also includes a anti- slosh filler neck, (larger diameter) and some other internal junk mounted through the top of the left front part of the tank, that had some plastic ducting running over to the left rear quarter brace.

here's a picture of some of the trunk mounted system......