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Unless the tank is full the car stalls right after a hard right turn. Many people with the problem have replaced the screen/strainer in the tank and problem solved - I tried that did not help. I checked the vent hose coming out of the sending unit in trunk area. Im assuming the one on the right is the vent hose, pumped some air in the line and had a friend place finger over vent line that goes to charcol canister. Very little air came through and now no air comes through in fact some fuel spit back out of the line.
Check to see if the round baffle at the bottom of the tank has broken free. It keeps a small amount of fuel around the strainer under corning. You''ll have to remove the sending unit to see it. (assuming this is a late car, not sure if the metal tanks had the baffle)
Yes I have drained the tank and inspected inside. The round baffle is there, although it not fastened down I assume once the sender sits in the hole the thing doesn't move - correct? Im now looking at fuel vent line that goes from the tank to front of car that ends at the charcol canister. Since its a race car I removed the canister a long time ago. Last night we unplugged the vent line attaching to the top of the fuel sender and blew compressed air into it, my helper put his finger where the line ends (where the canister used to be) and no air came though. Fuel actually blew out of the line, so now Im wondering if the line is blocked and would this cause the stumble.
Again this situation is, when we run with 13 gallons or less, take a hard right turn immediate stumble, lift off the throttle and it corrects, hit a hard left turn runs great. Fill the tank to the top the problem goes away (until you get to about 1/2 to 3/4 then stumbles). Has a new fuel filter, pump, new in-tank strainer, checked all the wiring.
I see no way that you could uncover the fuel inlet with even 5 gallons of fuel in the tank, much less 13. Have you considered that you are opening the wiring to the fuel pump due to something shifting under the G loads? I know, easy for me to say and hard to diagnose. If you really want to rule this out you could run a separate wire to the fuel pump from the battery. Put it on a toggle switch so you could turn it on during a track session just long enough to prove your point. Even so, why would something electrical be dependent on the fuel in the tank? This is a real mystery for sure.
I am yet to fully understand the engineering behind the hose setup but it has more components than one would suspect. Under the metal cover in the rear compartment, right hand side, there is a check valve and a little plastic surge tank buried up in the C pillar.
I got rid of the charcoal container long ago. Interestingly enough, I build up a positive pressure in my fuel tank after runs on hot days. As far as the positive pressure is concerned, my understanding is that the excess gasoline that is returned from the fuel pressure regulator is heated as it passes through the engine compartment, causing it's volume to expand. My tank must be sealed against a positive pressure, since I get quite a outward "whoosh" when I release the gas cap after coming in from a hot run. I'm going to guess that the check valve part lets air in to replace fuel as it is burned but in the other direction doesn't let the fumes out.
I do know that if you just run the vent hose from the top of the tank directly to an open end sticking out of the car at the fuel filler, you will spew gasoline in a major way while turning left. That experiment led me to going back to substantially the stock setup, except the line going to the charcoal canister now exits at the fuel filler area.
Yes I have drained the tank and inspected inside. The round baffle is there, although it not fastened down I assume once the sender sits in the hole the thing doesn't move - correct? Im now looking at fuel vent line that goes from the tank to front of car that ends at the charcol canister. Since its a race car I removed the canister a long time ago. Last night we unplugged the vent line attaching to the top of the fuel sender and blew compressed air into it, my helper put his finger where the line ends (where the canister used to be) and no air came though. Fuel actually blew out of the line, so now Im wondering if the line is blocked and would this cause the stumble.
Again this situation is, when we run with 13 gallons or less, take a hard right turn immediate stumble, lift off the throttle and it corrects, hit a hard left turn runs great. Fill the tank to the top the problem goes away (until you get to about 1/2 to 3/4 then stumbles). Has a new fuel filter, pump, new in-tank strainer, checked all the wiring.
If it's loose, that is going to be your problem. Been there done that on our endurance car.
I see no way that you could uncover the fuel inlet with even 5 gallons of fuel in the tank, much less 13. Have you considered that you are opening the wiring to the fuel pump due to something shifting under the G loads? I know, easy for me to say and hard to diagnose. If you really want to rule this out you could run a separate wire to the fuel pump from the battery. Put it on a toggle switch so you could turn it on during a track session just long enough to prove your point. Even so, why would something electrical be dependent on the fuel in the tank? This is a real mystery for sure.
I am yet to fully understand the engineering behind the hose setup but it has more components than one would suspect. Under the metal cover in the rear compartment, right hand side, there is a check valve and a little plastic surge tank buried up in the C pillar.
I got rid of the charcoal container long ago. Interestingly enough, I build up a positive pressure in my fuel tank after runs on hot days. As far as the positive pressure is concerned, my understanding is that the excess gasoline that is returned from the fuel pressure regulator is heated as it passes through the engine compartment, causing it's volume to expand. My tank must be sealed against a positive pressure, since I get quite a outward "whoosh" when I release the gas cap after coming in from a hot run. I'm going to guess that the check valve part lets air in to replace fuel as it is burned but in the other direction doesn't let the fumes out.
I do know that if you just run the vent hose from the top of the tank directly to an open end sticking out of the car at the fuel filler, you will spew gasoline in a major way while turning left. That experiment led me to going back to substantially the stock setup, except the line going to the charcoal canister now exits at the fuel filler area.
Wish I could offer more help!
Make sure you vent the tank. I've seen the hatch floor deform from the tank bulging under pressure, and a scary amount of pressure under the gas cap. This seems to creating a bomb. You may have to drop the tank. I've seen the plastic nipples on the top of the tank plug, and fracture.
The lid for the round baffle is loose, this lid prevents fuel sloshing out of round baffle. need to take fuel sender out and look , it snaps into place . You a small hand to do this. My daughter had to do this for me.
Oh wait Porsche Doc you're talking about if the baffle is loose correct? Yeah the plastic thing (looks like a plastic bowl) that sits over the screen in the bottom of the tank moves around its not secured into place. But it has the cover with a hole that the sending fits into, once you put the sender in doesnt that secure everything in place?
No, the bowl is a spiral baffle and it should be fixed/attached to the bottom of the tank. There is a cover with a hole in it for the bottom of the sender. The cover should snap onto the baffle. All should be secure, nothing loose.
09-12-2016, 10:11 PM
944 Race car stumbles hard right turns
