I actually feel a bit foolish asking about this problem, because the answer must be very obvious. Anyway, I have just finished restoring my Series 1 400i 39313 after years of restoration work, which included a full overhaul of the fuel system. Both fuel tanks were removed and cleaned, suction filters removed and cleaned, new fuel pumps and accumulators, WURs stripped and restored etc etc. The tank vent pipework was not changed in any way. After reassembly, fresh fuel was used for the initial start-up, introduced into the fuel filler by siphon from fuel containers. The car is running beautifully, starting, running and idling perfectly. Ten days or so ago I brought the car to the fuel/gas station to fill the tank prior to going on a 150 mile trip to celebrate its completion. The fuel gauge was reading less than 1/4 full, but after introducing approximately 40 litres of fuel the filler pipe was overflowing, as it would be if the tank was completely full. I tried to introduce more fuel, reducing the flow rate from the filling nozzle, but to no avail. I could see liquid fuel welling up in the filler neck. When I got back into the car, the fuel gauge was reading a somewhat over 1/2 full. After the 150 mile trip (during which the car performed faultlessly) the fuel gauge was again below 1/4 full, so I again tried to fill the tank at a different fuel station. Exactly the same experience as before, fuel welling up in the filler neck after adding around 45 litres, and the fuel gauge reading 1/2 full. So I assumed the fuel gauge or sender was faulty, and removed the sender. I could then see that the level in the fuel tank was approx 105mm (4") below the top of the tank, which would represent approx 60% full (assuming the tank is designed to utilise its full volumetric capacity). I overhauled the sender "while I was there" and checked out the resistance change over the full range of movement of the float arm, all was OK. After replacing the sender, I added a further 17 litres of fuel to the tank by siphon (very low flow rate) and the fuel gauge rose to a shade below 3/4 full, which roughly corresponds to the observed level in the tank. In summary, the situation I have is that under normal fuel/gas station filling conditions, the fuel filler/tank combo shows an overflow condition when the tank is physically only half full. Up to that point, fuel flows into the tank(s) without a problem. The obvious place to look would be the tank venting arrangements, but I can see nothing wrong with the routing of the vent pipework. I don't think I made any change to the position of the vent hoses, but since this work extended over four years or so, I can't be 100% sure. Has anyone else experienced something similar?
Have you compared your fuel system to the 400i SPC figure?: https://www.ferrariparts.co.uk/diagram/ferrari/400i/009-fuel-tanks--pumps--lines Tube 11 to charcoal canister 7 to tube 8 to filler pipe 4 has to be a clear, open (kink-free) air path; otherwise, the (mostly top portion of the) tank with the level sender in it can't fill up. Just a thought for something to check.
That was my first thought as well. Something is preventing both tanks to be filled and so the overflow occurs when the first tank is filled, your gauge shows only halfway, you use that fuel and the gauge falls to 1/4. Unlike the old Jaguar XJ6 with two separate fuel tanks and fillers, the 400i's two reservoirs (tanks) should get filled from the same filler with a cross over pipe between the two.
There are some vent hoses that are routed against the rear firewall (bacķ of the rear seats). On my car these vents are passing through a small flat charcoal canister. Maybe It is plugged? All the above are hidden by the carpet trims of the firewall.
Thanks to everyone for the replies, and to Steve for the link to the parts list. If you mean Hose 20 from the first (left hand) tank, I don't think this can be the answer, because the second (right hand) tank in which the sender is fitted is filling up to 50 to 60% of maximum capacity. It can only fill if there is a clear path from the LH tank through the so-called "Bridge Tank" Agreed. I can't get back to the car before next week to check out all the vent pipework, I will update after inspection. Again, the second tank is being filled as I said above to 50 or 60% of capacity. The quantity of fuel added corresponds fairly well to the typical mpg figure and the distance travelled. While I don't have an easy way to see the actual fuel level in the first (LH) tank, the level visually observed in the RH tank after removing the sender ties in with the gauge readings, the estimated fuel consumption and quantity of fuel added. There's no evidence to suggest that the fuel levels in both tanks are not equal (if that is what Ashman is suggesting). Except perhaps during the actual filling process, because if the RH tank vent pipe was partially blocked as Steve has suggested, then the LH tank might overflow before the RH tank would fill, due to backpressure building up in the RH tank. After some indeterminate time, which could be just a few minutes, the backpressure would diminish and the levels would equilibrate. Next week I will focus on the vent line through the charcoal canister to see if anything shows up.
Agree with raemin. I had pluggage with hoses to or the drain from item #7, the canister, in the diagram. They easily blew clean with a bit of air pressure. My charcoal cannister was forward on engine firewall and that was previously plugged and got removed! Ken
OK, time to eat crow! Turns out I did something really stoooopid. On my car, there are three hoses exiting from behind the boot/trunk trim on the RH side, over the RH fuel tank. Two are larger bore (15mm approx) and one is smaller. The latter is clearly a body drain. Of the two larger hoses, one is a plain smooth finish plastic hose. The other is an externally braided hose identical to the fuel pump inlet hoses. I assumed the braided hose was the tank vent line, and I connected this to the RH fuel tank vent pipe. Wrong! With the help of the parts diagram, and after pulling back the carpet trim to trace the pipework properly, I reconnected the plastic hose to the tank vent after verifying that it was not obstructed in any way. Happy days. I still can't figure out where the body end of the braided hose is connected to. It disappears behind the upper right hand side of the seat back/firewall. The free end is connected to a drain tube exiting through the trunk floor. The body end is at least partially obstructed, enough to explain the backpressure and the filling problem. Just for clarity, on my car there are two body drain hoses on each side of the trunk exiting through the trunk floor just behind the wheel arches. Thanks to everyone who helped solve this issue.
