PorscheDoc

Ok, so Aaron's car is sitting in my garage. I put vacuum on the valve on the driver's fender and it holds pressure fine. When pulling the large hose off of it, there is definitely fuel residue. I'll pull the canister today, and fully expect to find fuel, as when we drained his tank, we had charcoal particles in the thank. Vacuum line to the valve is running to the top of the TB and looks intact.

I've never run across this problem before, ideas?

AaronR968

Rut Roh, I've stumped the Doc...

PorscheDoc

Ok, so pulled the canister. Pretty soaked with gas. Charcoal coming out the bottom of it into the vent line (that dumps behind the gas tank).

The larger hose running from the shut off valve at the drivers fender was loose at the intake manifold. The rubber cap that is on the T fitting just off that connection, was completely disintegrated, so we definitely had 2 vacuum leaks. I assume this would cause a malfunction in the gas tank vent valve which is the next item between the hose and the shut off valve?


1. Would that cause the gas build up in the canister? The vacuum line that runs from the shutoff valve to the top of the throttle body has no vacuum. I can blow and stuck through the line freely. The shut off valve does hold vacuum. Should there be vacuum there with the car at idle? I assume there has to be?
2. I assume there is a filter screen in the bottom of the canister that keeps the charcoal from getting into the bottom vent line? That is obviously shredded if it is allowing particles through the vent line and out the back of the car. I blew it out with compressed air and had about a half a cup of gas and charcoal shoot out the back of the car on the ground, lol.

Guess I'll have to pull out the manuals, lol.

AaronR968

You get my text?

Jaap968

I was trying to locate where the vent line (to atmospere) would exit from the canister. So it is located behind gas tank?

As far as I understand the fuel vapors stored in the canister are only burned off when engine has reached certain operating temperature so may be difficult to diagnose with engine cold.

Jaap

PorscheDoc

Correct, if you look from the rear, the upper passenger side area you will see a spout. It literally drains down the back of the tank and down the wheel well if you blow it out, lol.

wilhelm

I have been going through the same issues, mine started with hesitation and I eventually killed 2 fuel pumps. All hoses have checked out, when I pulled the canister gas and charcoal leaked out of the bottom.

The one line from the canister to the tank goes to a shut off valve 928 201 083 02 next to the fuel filler neck. Then from the shut off valve to the expansion tank, then to the fuel tank through the tank gauge. The parts catalog has the best diagrams but you have to link several pictures together to see how everything connects.

I'm guessing the only way fuel can get in the canister is if the shut off valve 928 201 083 02 is broken, I have one on order. I'm also assuming that if charcoal and gas come out of the bottom of the canister that means the canister is bad too. Not sure how charcoal could make it into the fuel tank.

wilhelm

PorscheDoc just read your blog and its very similar to my experiences. My fuel sender had been broken for awhile, when I pulled the sender to replace it was destroyed. I drained the tank, replaced the fuel screen at the bottom of the tank, and replaced the fuel sender then went through a full tank without any hesitations. Just after filling the tank the second time the fuel pump died. 3 days and 200 miles later my car stalled twice then died with another bad fuel pump. When replacing the pump I noticed my tank was dented bad which might have happened earlier causing the old fuel sender to get destroyed. Saw another post here describing the same dented tank possibly cause by venting issues.

Any chance you can take some pics of the bottom of the tank to see what it looks like? I will try to get some pics of mine too.

wpb968

Doc, Thanks for the pictures in your blog. I have a fuel smell issue also. I had a visible fuel leak at the check valve/banjo bolt on the fuel pump. I replaced the check valve and all of the tank/fuel pump/filter/hardline fuel hoses. No more leak, but still have a faint fuel smell. I will check the charcoal canister and vacuum lines and the shut off valve. Many thanks!

PorscheDoc

FYI: A charcoal canister is about $150 bucks from sunset. It is the same canister used on a 993, but different from the 944. We opted to cap the intake for right now (bypass the evap system since we are evil men and don't have emissions testing here), and install a filter in place of the canister on the line going back to the tank. I had the entire system removed from my 951 track car and never had any issues. We should be able to tell in the next couple of tanks of gas, if there is gas residue dripping out the filter in the wheel well. If it does appear, then we will go after the shutoff valve next. I can only imagine how fun that will be to replace. I think someone has been into the fill tube area and really glued that cover down more than it should be. Fun fun. So far after driving the car, filling it full of gas, etc, we don't have anymore of the tank pressurization issues. Now aaron will just have to drive it for awhile to see what it does.

AaronR968

A huge thank you to Karl! In case you guys didn't realize it, he is the man!! I hope all is well. I will report back after a few tanks.

Jaap968

I think the shut off valve near the filler neck is a safety feature that should normally be always open to let vapor out or air in and only close (operated by gravity) when the car rolls over to stop fuel from running out.
The valve(s) in the engine bay are used to burn of excess vapor from the canister under normal operating conditions. I found some interesting treads on the 928 forum where someone had these valves stuck open so the engine pulled a vacuum all the time and imploded the tank. Eventhough the canister has a vent line to outside air this appearred not enough to compensate for the constant vacuum caused by the valve(s) stuck open. I could imaging this could even suck fuel from the tank into the canister.

Jaap

JarmoL

Hi there

I have been suffering same symptoms as the original poster has. I am also having problems on tight right hand turns while at the track. Car hesitates if the fuel tank is only half full. I think it's the swirl pot inside the tank that's broken like Porsche Doc explained.

Can anyone confirm that the line from the expansion tank to carbon canister should be open both ways? I tried blowing air from canister towads the fuel tank but the line seems to be blocked. Maybe it's the shut off valve that's broken?

Jarmo

Jaap968

As far as I have been able to test and derive from schematics the line should be open both ways (except when the car is upside down in which case the shutoff valve will close). However on my car it takes some pressure to force air back from canister to tank and vice versa. But looking at all the bends this line makes I suppose that is to be expected? Or maybe a line has collapsed/valve is blocked. Probably going to have a look under the cover inside the hatch area to verify.

Jaap

wilhelm

Are you just trying to force air from the canister into the tank? In the hatch, pull the cover to the fuel sender, remove the hose on the right side of the sender, and see if you can feel the air. This line goes to the expansion tank, shutoff valve, then to canister. I was able to feel air clearly from the canister to before the shutoff valve at the filler neck but its a pain to get to this valve, easier to test at the fuel sender.

I installed a filter just after the shutoff valve, no more canister, and so far no hesitations or pressure in the tank.