No Start After Fueling - Where best to begin?

Refueled twice on an out of town trip this weekend. Hot weather. Both times, the engine would crank/spin fine on the starter but would not start. It would "hit" but not keep running. The first time, on my fourth try, I left the key in the "on" position for a few seconds before trying to start it and it started. The second time, on my third try, I pressed the throttle slightly while trying to start it and it started. The other times I started the car on this trip, it started fine and it ran great for the entire trip, even after the difficult starts. I did not get any CEL messages. I know that the vent valve is suspect on these cars, but do these symptoms point primarily to this or to something else? I know some have changed a valve or two at the engine end of the fuel system to cure starting problems. Just trying to figure out where the percentages are highest to fix this on the first try. Any suggestions?

With no CELs, the first place I would look is the ignition switch. The plastic cylinder that contains the contacts is located behind the lock cylinder. They are not very expensive. There are YouTube videos documenting the change out process. A common failure in the 996. The circiut and contacts for engaging the starter solenoid is different than the circuit that energizes the ignition. You can spin the starter motor with no power to the ignition. It can be an intermittent failure. Sometimes it starts, sometimes it doesn't. The second place I would look is the fuel pump. I had one fail on my Mustang GT and it was an intermittent failure at first.

I had this exact problem, with the exact symptoms, and this fixed it: https://www.pelicanparts.com/techart...Vent_Valve.htm Note that the how to does not deal with the microswitch that the fuel line vent valve holds onto the filler neck. When you remove the valve, there will be a little "sensor" on a wire. If you look at the valve it will be obvious where it goes. It wasn't so obvious for me, and took me hours to figure out. But now you know, and knowing is half the battle. The other half of the battle involves guns.

As said - Ignition switch - next time jiggle the key in the ignition and see if works. As said - if it seems to always happen after fueling then the vent valve might be out of place (or need to be replaced) Year/Model? Do you have E-gas? Have you done a e-gas calibration lately? Then it jumps to more difficult things - fuel pressure regulator, vacuum leaks, fuel pump, CPS on the way out Recent maintenance? Plugs and coils?

Since the issue seems so connected to refueling I guess I will just go with the vent valve. Car info is in my signature but maybe you don�t see that on the mobile version? 2004 C2 6 speed.

Look at the regeneration valve in the engine compartment. Google part # 996-110-129-53-M100 One of the most common causes of no start after fueling is when this valve fails open and allows fuel vapor to be pulled into the throttle body behind the throttle plate. This causes a rich mix at warm start, opening the throttle helps lean it out enabling start. Much like your old carbureted car when it was flooded. https://www.pelicanparts.com/cgi-bin...10-129-53-M100

I see Pelican also offers a Bosch branded equivalent for $46 versus $220 or so for the Porsche part. Tempting. I see it does not come with the plastic tube connector but can be rigged to work.

You can reuse the tube by heating it (hair dryer?) and working it off by pushing it off using a screw driver against the end of the tubing. If you try to pull it off you get the *"Chinese" finger trap effect. it just stretches tighter. * https://www.ziggosparty.com/products...RoCfwgQAvD_BwE

So I ordered the Bosch part for $26 on Amazon. I had planned to use my heat gun to work the tube, so we will see how it goes. If I do this and learn something and/or succeed I will document it here.

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I had the exact same failure symptoms and the Regeneration Valve was at fault. In my research it looks like the failure of either the Fuel Vent Valve as posted by strathconaman or the Regeneration Valve can cause the exact same no hot-start symptom. Although both are prone to failure, after a bunch of reading it looked like the Regeneration Valve was slightly more prone to failure presumably due to the constant engine bay heat. And since it was so easy to replace (literally takes 5 minutes) I decided to try that one first and in my case that was the culprit. But it could have just as easily been the Fuel Vent Valve. Good luck. Luckily neither one is too expensive and both are pretty easy jobs.

I bench tested the so called regeneration valve today. It "clicks" nicely when energized and holds vacuum, so I think it is OK. Moving on to the fuel tank vent valve.

Jim, I think you can hear the click and the rejeration valve can still be at fault. From reading through this thread, there appears to be a screen inside that valve that can become clogged. In other words, I think the problem is not whether it hold vacuum, but whether it actually allows extra air into the throttle body when it needs to. A clogged valve will have no problem holding vacuum. I did not try this when I replaced mine, but you may want to see if you can actually blow through that valve to confirm it is really open. There is a big discussion on a very similar issue in this thread. https://rennlist.com/forums/996-foru...m-pics-11.html

How can I simulate refueling to test the success of whatever work I do? How does the ECU know that the car has been refueled? Is it a switch on the flapper inside the neck or does it get a change in fuel level from the sender in the tank or ???? Chris - I hear you on my bench test perhaps not being conclusive. Since I have the vent valve on order, I may as well install it and see what happens. Would be nice to test safely at home in the shop rather than alongside the fuel pump at the gas station.

I think the car can tell when it has been refueled because of the reed switch on the filler tube. I know the car detects when it has been refueled because my oil level detector sometimes indicates a very long wait (like 40 or 50 minutes) after refueling, but when it starts up in the morning it checks the oil level in like 10 seconds. Strange quark....

Just to wrap this up and add a dot on the curve, I did replace the vent valve. I have only refueled once since then, but the car started normally afterwards. As noted, I did test the regeneration valve and decided to leave it in place. So this result is from changing only the vent valve at the fuel filler neck.