Fred111

My new-to-me Boxster with 233,000 miles won't start after gas fill up without mashing the gas pedal. In searching this problem I see cayennes have the same trouble and it's the fuel tank vent valve. Do we have the same animal? I've only filled up twice and happened both times. I just changed the AOS and after about 85 miles got a cel with P0446, 1128, 1130. Other than the trouble starting after fill up it runs good.

Macster

Don't know if the Cayenne and Boxster share the same hardware in this area. Could be. The function is common to all vehicles.

There is a shut off valve which is used to close the purge air line to the charcoal canister while the DME is running a fuel tank leak test (a pressure test to confirm the fuel system is not open to atmosphere).

While the test is running if the shut off valve is not working, or an air line is blocked, or air flow through the canister is too high, the P0446 code is logged.

The canister purge valve and purge air lines have to be checked for proper operation and no blockage. If the valve or lines are bad (or sometimes the lines can get blocked) the problem is then with the canister. It has been damaged by exposure to liquid fuel or the canister has suffered a mechanical failure and the charcoal has come loose and is clogging the air lines.

A side effect of a problem is the fuel tank can become pressurized (or subject to low pressure) and the engine can be hard to start under these conditions.

When you remove the gas cap do you hear a hiss? (Either from pressure escaping or air rushing into the tank past the cap.) If so this is a sign the venting system has a problem.

Fred111

I'll have to check the cap to see if I hear anything. I can't remember.
Looking over on the 968forum last night several people had reported the same problem. They had taken care of it with replacing the regeneration valve under the intake. Does that sound correct? One of them even had the same codes I had.

Macster

The code arises from a couple of different failure modes that essentially affect the isolation of the fuel tank and atmosphere. One failure mode is a bad valve. If owners have replaced the valve and codes have stayed away the valve was the failure. One can't argue with the success.

KevinH2000

I had the same problem when my Boxster had 45k on it. It required two visits to the shop to fix it. I first had the air vent line replaced - part number 996-110-129-05.

I had a CEL after that and replaced the activated charcoal canister 996-201-221-07 and the shut off valve 996-605-201-01.

The technician suggested that the previous owner had been topping off the tank when he filled it with gas. This caused fuel to get into the charcoal canister and other parts of the vent system which eventually damaged the components. Prior to that, my MAF had failed causing a backfire. That could also have contributed to the problem.

Fred111

I wanted to post a follow up after I changed the regeneration valve. No more coke-bottle hum, no more hard start after fill up and my idle has settled down! Woo hoo!


aft

Macster

Very good. Thanks for the update.

Schnell Gelb

This video may help.
The system is electrically controlled - so there is a fuse to check also - see manual.

Fred111

The valve in the video is not the one I replaced. I changed the regeneration valve which is under the intake manifold. It seems to be connected to this valve though.

Alex Sol

got these numbers from pelicanparts

Porsche part# 996-110-129-06-M14

Bosch 0-280-142-380

doesn't include the rubber line and costs $45

dr914

I was just going to mention the fuse