Gasoline Vapor - Evap System Troubleshooting

[GDane]

Hi,
New member with recently purchased 1970 124 Spider in the Northeast US.
This is my third one; my first 2 cars, decades ago, were 1974s.
This 1970 car is an 8 YO bare metal restoration and is in excellent shape.
However, it fills a 3 car garage with gasoline vapor over night.
The smell seems to come from the area below the trunk, but inside the car, around the gas tank, but no evidence of gasoline leaks.
I suspect a problem somewhere with the evaporative emission control system.
The PO tells me his detailer erroneously plugged the top vent on the charcoal canister in the engine compartment (but top vent now open), and suggests that may have caused a failure in the evap emission control system, but had no additional guidance because, like me, he does not know how it works.
I've searched and cannot find a complete illustration of this system and its components, nor any explanation for how it is supposed to function.
Any guidance on where to find information about how the system works or troubleshooting it would be super appreciated!
Thanks!
G. Dane

PS: Guidance on the forum process and etiquette appreciated; this is the only forum like this on which I have attempted substantive information exchange.

[ORFORD2004]

file:///C:/Users/Dell/Downloads/Fiat%20Emissions%20manual.pdf

[ORFORD2004]

https://mirafiori.com/forum/viewtopic.php?t=99621

[18Fiatsandcounting]

I didn't think the 1970 spider had much in the way of evaporative emissions control, but apparently I'm wrong (my '69 spider has none while my '71 does have a charcoal canister). Can you describe what you have in the trunk, in terms of hoses coming from the gas tank? Many of those old braided hoses may look OK on the outside, but they are becoming permeable to gas. Since gas evaporates quickly, you don't see it seep through the hoses but you can smell it.

The large elbow hose connecting the filler neck to the gas tank is often a source of leaks. Sometimes it looks OK, but if you squeeze it, gas might squirt out of small cracks. Anything over 20 years is suspect, but this one is rather tricky in that you have to drain the tank first. Use caution with all that.

So, in a nutshell, you just need to replace all the hoses going to and from the tank in the rear. Get several feet of the right diameter and then cut the lengths you need with a razor blade. Buy hose rated for fuel, and I'd suggest getting hose rated for ethanol as well. An auto parts store can help you with all this.

-Bryan

[GDane]

Thanks @18Fiatsandcounting!

I see the fuel tank, an electric fuel pump with a fuel filter mounted on the front wall of the space between the fuel tank and the spare tire, and a "Check Valve / Fuel Vapor Separator (Fiat All to 1978) - OE" (https://www.midwest-bayless.com/fiat-12 ... 78-oe.aspx) bolted in what appears to be the OEM position to the inside left wall of the space next to the fuel tank.

The top of the fuel tank has a metal port cover with what looks like wires for the fuel level gauge and 2 gas lines, one from the fuel pump and another coming out, presumably going to the engine bay. On the left side of the fuel tank, pointed to the left about 2/3 of the way back on the tank arefour additional lines. One of them appears to lead from the top of the fuel filler area back into the tank, I presume for overfill protection. That one's about 3/4 of an inch diameter and is plastic. The other three are probably 5/8 inch diameter and lead up to a plastic vessel that is about one cup in volume that is mounted vertically with the three lines coming out the bottom. There's a fourth line coming out from the bottom of that plastic vessel that leads to the check valve/fuel vapor separator. The three group lines are braided fuel lines. The line leading to the check valve is plastic. there is another plastic line leading from the other side of the check valve down, and presumably forward to the engine compartment.

I found the flexible lime from the bottom of the gas filler into the bottom of the gas tank that you mentioned. Interestingly, that hose looks like radiator hose. It's not in the best of condition and probably should be replaced, but it did not leak when I squeezed it, and the smell is definitely coming from around the gas tank on the inside, not outside.

The only other things I can think of that may be worth noting are that (1) the braided fuel lines do not look new, but they don't look as old as the car, and the electric fuel pump is clearly a newer installation because the braided fuel lines leading from that are darker in color, and (2) the clamps on all these hoses are a mix of the smooth sided "fuel injection" style, and the more common radiator clamp style with the machined slots in the band.

[GDane]

Thanks @18Fiatsandcounting!

I see the fuel tank, an electric fuel pump with a fuel filter mounted on the front wall of the space between the fuel tank and the spare tire, and a "Check Valve / Fuel Vapor Separator (Fiat All to 1978) - OE" (https://www.midwest-bayless.com/fiat-12 ... 78-oe.aspx) bolted in what appears to be the OEM position to the inside left wall of the space next to the fuel tank.

The top of the fuel tank has a metal port cover with what looks like wires for the fuel level gauge and 2 gas lines, one from the fuel pump and another coming out, presumably going to the engine bay. On the left side of the fuel tank, pointed to the left about 2/3 of the way back on the tank arefour additional lines. One of them appears to lead from the top of the fuel filler area back into the tank, I presume for overfill protection. That one's about 3/4 of an inch diameter and is plastic. The other three are probably 5/8 inch diameter and lead up to a plastic vessel that is about one cup in volume that is mounted vertically with the three lines coming out the bottom. There's a fourth line coming out from the bottom of that plastic vessel that leads to the check valve/fuel vapor separator. The three group lines are braided fuel lines. The line leading to the check valve is plastic. there is another plastic line leading from the other side of the check valve down, and presumably forward to the engine compartment.

I found the flexible lime from the bottom of the gas filler into the bottom of the gas tank that you mentioned. Interestingly, that hose looks like radiator hose. It's not in the best of condition and probably should be replaced, but it did not leak when I squeezed it, and the smell is definitely coming from around the gas tank on the inside, not outside.

The only other things I can think of that may be worth noting are that (1) the braided fuel lines do not look new, but they don't look as old as the car, and the electric fuel pump is clearly a newer installation because the braided fuel lines leading from that are darker in color, and (2) the clamps on all these hoses are a mix of the smooth sided "fuel injection" style, and the more common radiator clamp style with the machined slots in the band.

[18Fiatsandcounting]

For a stock 1970, the fuel pump would have been mechanical (up under the intake manifold on the engine), so an electric fuel pump was added at some point. Nothing wrong with that as long as there isn't something goofy going on. Electric fuel pumps tend to be higher pressure than mechanical ones, but that usually causes problems with "overpowering" the float valve in the carb.

The "metal port cover" should have 4 things coming out of it: A pink wire for the fuel gauge, a red/gray wire for the low fuel warning light, a larger (8mm) metal line for the hose to the fuel pump (originally this would have gone to the metal line up to the mechanical fuel pump on the engine), and a smaller (7mm) metal line for the fuel return from the carburetor. My '69 spider does not have a fuel return, but my '71 does, so I'm not sure what your 1970 has. Sounds like it has the fuel return line.

The larger hose from the side of the tank up to the fuel filler neck is exactly what you mentioned, a burp/overflow feature so gas doesn't slosh out as you fill the tank. The 3 smaller lines from the tank are vapor recovery, and the 3 lines inside the tank lead to different locations. These 3 lines go to a liquid/vapor separator, usually a round canister up under the inside fender, near where the tool kit is (if you still have it). The middle port of that canister goes to the Midwest-Bayless part that you showed.

However, the M-B part is a bit misleading. It is actually a 3-way valve that has a port that you don't normally think of, and that is to outside air. So, its function is to vent the tank if it gets overpressurized, admit air if you tank is developing a vacuum, and under normal conditions, route the vapors from that vapor canister up under the fender to a vapor return line up to the engine compartment.

This 3-way valve is really hard to find, and they almost always are bad. Your valve may be venting gas vapors to the trunk rather than back up to the engine compartment. There are workarounds such as bypassing the valve and leaving the gas cap very slightly loosened so that neither pressure nor vacuum can build up in the tank. Some people drill a small hole in the gas cap which does the same thing, but I'm always reluctant to do that.

By the way, do you have a charcoal canister in your car? Again, not sure about 1970, but 1969 didn't have them but 1971 did. So, my 1971 has three metal lines up to the engine compartment: fuel supply, fuel return, and vapor recovery. The charcoal canister is a metal box near the coolant overflow tank.

It sounds like either a combination of weak hoses, loose clamps, or a bad 3-way valve is the issue.

-Bryan

[GDane]

Thanks again. This is all super-helpful guidance.

Yes, I have a charcoal canister, but it’s the new style, this one: https://autoricambi.us/charcoal-or-vapo ... r-1980-on/
I guess that was part of the restoration.

The PO told me his detailer lost the loose plastic cap on the vent at the top of that part and replaced it with a stiff rubber cap in a mistaken attempt to make it airtight. I’m wondering if the extra pressure caused by the rubber cap failed the “three-way” valve in the trunk.

Also, the “three way” valve on my car has only 2 hoses coming out of it, so could it be venting into the trunk? But I can’t see another place on this part to attach a third line, so a bit confused on that … ?

Yes, I see the two worse on the port cover, one pink and one red/gray.

PO also installed the electic fuel pump because he thought it worked better with the Weber DFEV carb he also installed as part of the restoration.3

[18Fiatsandcounting]

Also, the “three way” valve on my car has only 2 hoses coming out of it, so could it be venting into the trunk? But I can’t see another place on this part to attach a third line, so a bit confused on that … ?

It's a common source of confusion. There are only two hoses to that valve (inlet from the separator and outlet back up to the engine compartment), but the third "port" is just an opening on the bottom with a small rubber flapper valve, a small screen, and a perforated opening to the outside world. In this case, to your trunk. That flapper often rots away or sticks open, causing gas vapors to just exit to the trunk.

-Bryan

[GDane]

@18Fiatsandcounting thanks much.

I imagine transporting the car 1000 miles with a half full tank in very hot weather and a plugged charcoal canister could generate enough pressure in the line to fail that third port flapper so that it sticks open.

I'll inspect and see if I can locate a new one, as well as change out all the hoses.

Thanks again for your guidance.

If you have any ideas on where to find a new one plz PM or email if you have the opportunity.

All the best,

[ORFORD2004]

https://www.midwest-bayless.com/p-22256 ... on-u8.aspx

[GDane]

@ORFORD2004 Thanks!