968 Fuel Stumble

Symptoms:
1. Fuel gauge that would randomly read different values, so you never knew how much gas was in the tank
2. Hesitation would appear after filling the car with gas.
3. Fuel smell
4. Lot of pressure released when opening the gas cap.

Last fall we had torn into the fuel system due to a hesitation it was having after filling up with gas. Aaron had also noticed that the tank let off a lot of pressure when opening the non-vented gas cap. I had found a bunch of black soot in the tank, so we cleared it out, replaced a torn in tank filter, and figured that would fix it. Not so much. After more thinking about it, we decided the black particles were probably somehow getting in the tank from the charcoal canister evap system. Something was definitely wrong for that to happen.

After some research, we figured out the fuel shut off/vacuum valve might be faulty, allowing the canister to fill with fuel and back flow to the tank. I put the vacuum tester on the valve and it held fine, so that shouldn’t be a problem. Following the line to the intake manifold, I found the hose loose at the manifold. Tightened that hose clamp up and all was good there. Further in line on the hose though, there was a capped off T-fitting. The cap was completely cracked and definitely causing a big vacuum leak. We are thinking this was probably the issue. Unfortunately, the charcoal canister was soaked with fuel, which must have disintegrated the internal screen, allowing the charcoal into the lines.

The vacuum valve is right on the driver’s side fender.

This hose down by the intake was loose.

And the rubber cap off the T-fitting.

I pulled the charcoal canister out of the driver’s fender well, and sure enough, soaked with fuel. The vent line was plugged with charcoal and gas. Hard to see in the picture.

I blew into the line to see if it was vented back to the tank. When I heard gasoline hitting the pavement behind the car, I realized it was vented on top of the tank. On the 944’s, it was vented in the drivers’ wheel well.

Next, I wanted to look inside the tank and see how much charcoal was back in it, so I pulled the fuel sending unit from the top (he was also having some weird level issues where the gauge would randomly read different levels. I have never seen this before, and I am not quite sure how it happened, but the fuel sending unit is not suppose to be bent! It sits completely inside the tank, so this car had to have taken a big hit to the rear or else the tank pressurized so badly that it caused the damage.

Here are the guts. The return tube is bent, as was the wire for the float gauge.

Now peering into the tank, it is hard to see, but there is a baffle system around where the fuel is sucked out of the tank to prevent sloshing and fuel starvation under hard cornering/braking/etc. The top of the baffle was completely separated from the lower section. I stuck my hand into the top hole and think, well that’s tight (I mean, what is the worst that can happen….so my hand could possibly get stuck in a gas tank…pffft….i’ve been in worse predicaments), and so I was just barely able to squeeze my hand into the tank (after draining it of course) to try and reattach the clips for the baffle. What I found though, was the bottom section was completely deformed, so the top piece wouldn’t clip into place like it should, so there isn’t much we can do about it without replacing the tank. Now at this point, my hand is stuck in a small hole in the top of a gas tank. If you have ever seen a dog get his leg caught in his leash or chain, or caught in a fence, you have seen how they start to panic and keep pulling like hell to get their leg free without really thinking about why they are stuck or how they could get out easier….yea, so I wasn’t quite at that point, but I was close. After retrieving my hand, I straightened out the sending unit and reinstalled it, and that at least seems to be reading correctly now.

Picture of my tank draining method 🙂

968Charcoal CanisterFuel Tank PressurePorsche