Cloud9...68

I'm referring to the one in the gas tank evap system. I'm not talking about the plastic reservoir on the drivers side of the engine compartment that catches the oil from the crankcase vapors and sends them back to the intake manifold. Thanks.

968workaholic

It should be under the plastic inner fender liner on the driver's side, behind the front wheel

Paul Waterloo

Yep...that's where it is.

Cloud9...68

Thanks, guys.

LM964

That's the one. It should be considered as a consumable and replaced at least once in the car's life.

The 964 has the same and when old/used is known to result in rough idling when hot or difficult start up when hot. I changed mine and it did make a difference.

PorscheG96

Interesting theory...

LM964

Charcoal cannister collects and stores vapors from the fuel tank when engine idling or stopped. During normal driving fuel vapours are drawn into the engine and burned.

As part of the evaporative emission system, if faulty it can lead to hard starting from warm/hot, errtic idle or poor acceleration if vapours are drawn into the engine at the wrong time. Apparently not associated with any cold start or running problems.

Took a while for me to find out the above, but when I changed the cannister in the 964 I never had any further rough idling or cut out issues when in long queues height of summer on French motorways...

Cloud9...68

I was asking because my car has developed an intermittent, but now apparently rapidly worsening, fuel leak from the area near where the fuel pump is located. It only leaks when the pump is running, which rules out a crack in the tank itself. I tried troubleshooting it last weekend, but I couldn't get it to happen, but when I started it last night, fuel was literally gushing from that spot, so I will investigate further, hopefully today.

The reason I asked about the canister is because someone on a different Rennlist forum theorized that I could have a clog somewhere in the evap system, and if I have a small crack in one of the 25-year-old hoses near the pump, the pressure build-up from the vapors that have nowhere to go because of the clog causes fuel to leak from the crack. Since it's a track car that's only driven on the street to and from the track, one option would be to get rid of the entire system, and just vent the tank directly to atmosphere, but I'm having second thoughts about that, because I don't want gas fumes in my garage on hot days, of which there are many in Texas. I'll let everybody know what I find. Thanks for the inputs.

Paul Waterloo

Here's a thread of mine with a bunch of pictures including pictures of fuel tanks removed from the car that I found on the net.....that might help you.

https://rennlist.com/forums/968-foru...in-my-fix.html

LM964

Did you manage to investigate further and find a root cause? 5 years ago I had a similar issue - fuel leaking from around the pump when running. Turned out to be a hose not fully tightened up after resto work that was done. In your case, this only occurs when the system is under pressure from fuel pump onwards. I agree re thoughts of pulling the evaporator/vent system as emission/fuel efficiency probably not top of the list for track day requirements What have others (track pilots) done?

Cloud9...68

Thanks for everybody's inputs - investigating this is my No. 1 priority for today. I thought of a way to test the theory of a clog somewhere in the evap system causing pressure to build up and opening up a small crack in a hose - if the leak stops when I remove the gas cap (thereby de-pressurizing the tank), it confirms the theory. Given that the magnitude of the leak has rapidly escalated, I'm more inclined to think its a cracked hose that will leak whether there is a clogs somewhere or not, or a loose fitting. I'll let everybody know.

Cloud9...68

Well, I released the fuel pump from the hose clamp that attaches the pump to its housing so I could get a good look at all the lines, jumpered the DME relay, and again, nothing, which is very weird considering how fuel was literally gushing out on Friday night. I let the pump run for a minute or so, but didn't want to run down the tiny lithium ion phosphate battery (it is a track car, remember), so I started it up, and let it run for a few minutes. Finally, I saw the makings of a droplet of fuel around the fittings on the outlet side of the pump, as can be seen in this image:

http://cdn4.pelicanparts.com/techart...mall/pic08.jpg

Over time, the droplet got bigger, and there is no sign of any other leaks upstream in any of the other lines. The leak is happening directly under the fuel pump, so it does appear that I've identified its source. But what has me puzzled is why the severity of the leak varies so much. I only started it up long enough on Friday night to pull it out of my driveway to allow me to turn the car around in the garage because I had some other work to do on the car on the drivers side, which normally is against the garage wall. In that time, A LOT of fuel spilled out, enough to stink up the garage to the point where my wife didn't want to bring her car in. Yet today, takes at least ten minutes of running to form a drop large enough to drip onto the ground. I checked the tightness of the securing nuts, and they appear to be plenty tight.

Some of the possible contributing factors are that today, I have the rear of the car up on jack stands, whereas on Friday night, all four wheels were on the ground. Also, the leak seems to be worse when the fuel pump is secured in place by the hose clamp that goes around. I tried holding the pump in it normal mounting spot to mimic its normal orientation, but that didn't make it leak any faster. It is significantly cooler today, although it was only in the high seventies or low eighties on Friday night, which is unusually warm for this time of year, but not hot my any means. Any ideas as to what could be causing this weird intermitttency?

As far as the leak itself, does anybody know if it's common for fuel pumps to start leaking in this spot? I'm sure it's the original pump (so it's 25 years old), but is it likely to be just the seals (referred to as "sealing rings" in the parts catalog), or should I go ahead and replace the entire pump? It isn't hard to take on and off, so I suppose I could try replacing the three seals fist, and if that doesn't fix it, replace the pump. Anybody ever run across a problem with symptoms like this? And I suppose the theory that there's a clop in the evap system causing excess pressure build-up could still be a contributing factor, as a pressurized system could cause a marginal sealing ring to vary in its ability to seal. Thanks.

Paul Waterloo

Here's the picture you reference above:



Is that fitting on the high pressure side? From what you are describing, you have some kind of leak that is most likely getting worse when everything comes up to temperature and then maybe you go over a bump and it stresses a crack open. I would suggest a fuel line.

Cloud9...68

Yes, it's the fitting on the high pressure side. The weird thing is that the fuel gusher I'm intermittently seeing isn't triggered by going over a bump, or by temperature. It has happened on two recent occasions - the first after a 20-mile mostly-highway drive back from the track, at the very end of the drive as I was about to pull into my driveway. The second, even more severe instance was immediately after I started it in my garage this past Friday night. The temperature was in the mid-to-high seventies both times. On both occasions, the fuel pump was securely attached to its housing. I have tried to reproduce the problem on multiple other occasions with the fuel pump out of its housing so I could get a good look at it and its fittings, without much success, and letting it run for 15 minutes or more doesn't cause the gusher to happen. It is dripping right below the fuel pump, and I did see the fittings on the high pressure side develop a droplet of fuel this afternoon, so it seems that it must be coming from the sealing rings on the high pressure side, but it's so bizarre that it isn't leaking consistently. I am seriously stumped, and obviously afraid to drive it.

Oh, and I checked the fuel lines in the neighborhood of where the leak is originating, and they are all bone dry.

LM964

Just out of interest (and seemingly irrelevant), have you tried swapping out the pump (used, borrowed or bought)?