Post Fill up "Coughing Spells"

[Pierre's Porsche]

My 2000 Boxster base (late year mfg. 10/99), is experiencing a recurring issue that's occurred four times in past three months all under same conditions....

I fill up with gasoline (no topping off, I stop when pump first shuts off), and drive home approximately 4 miles.

Next morning when I start car all is good until I get about 1/2 mile down the road through my subdivision. The engine starts "chocking" which appears to be intermittent shut off of fuel to cylinders, like I was running out of gas.

Until today I"ve been able to keep the car running through this "coughing spell," which lasts about 10-20 seconds, then car begins and continues to run fine. Today for the first time the engine stalled. It took me three attempts with a bit of pedal pushing on third attempt to start the car. Again after about 10-20 second coughing spell it ran fine.

This only happens when I park over night directly after a fill up. When I fill up and continue to drive for a while no problems....No check engine light illumination so far...

I'm perplexed. Thanks in advance for a response!

[Loren]

You need to have the car checked for pending fault codes. You will need Durametric, a PST2, or Porsche PIWIS tester to see pending fault codes.

When was the last time the fuel filter was changed?

You might also want to check the fuel pump output (after checking the fuel filter).

[Pierre's Porsche]

Thanks for response and suggestions Loren.

I Checked for pending codes, using an Actron device. No pending codes. (Durametric software arrived yesterday. Going to Wallyworld for laptop later today, will recheck).

I replaced the fuel filter less than 5K miles ago (about six months).

Haven't check fuel pump output. but i think it's fine. No other indication of poor fuel supply except under condition described above.

I'm thinking it's the Evaporative Canister Shut off valve beginning to fail...this winter it would click loudly, no click this summer...My suspicion is the ECM opens the Purge Valve to the engine throttle body, but the Evaporative Canister Shut off valve sometimes sticks shut. Thus causing a brief "fuel starving" condition... Am I off base..?

[Pierre's Porsche]

Loren,

So I bought Durametric tool and used it to check my systems this weekend. The Evaporative Canister Shut Off valve worked fine when "activated" using Durametric. However when I tried to activiate the Evap. Canister Purge Valve, the software displayed the typical "wait" symbol that software presents when it's working, but it did not appear to activate the purge valve. Does Durametric software give you a "command failed" or other notice when an activation request fails..?

[Loren]

Not sure about the Durametric test - I think it just switches the valve.

You can test the valve and tubing by blowing (low pressure) air through them.

[Pierre's Porsche]

Final Update: Problem Solved.

So after several more coughing spells and a few P1140 CEL Codes thrown, I figured out the failed part and repaired it.

The problem was the Evaporative Canister Purge Valve (the valve located under the intake plenum). I determined this by removing the hose connection at the intake, and sucking on the end of the tube with the engine off and cold. It would not hold a vacuum as it should.

Replacement of the valve was essentially a snap, minus one screw. That exception being the the screw that holds a mounting strap for connecting the purge valve hose to the underside of the intake plenum. What a PITA! Took me four hours to remove this one screw and an hour and half to replace. So here's what I learned. Use the longest and thinnest 8mm open/box end wrench you can get your hands on.

To remove this mounting strap screw, you'll need to loosen all six mounting bolts that connect the intake plenum to the head. Start in the middle and work your way out. Do not entirely remove these bolts, simply back them out about 3/4 of an inch. Now, from inside the car cabin lift up on intake plenum and use a plastic body panel tool to wedge between the plastic plenum and cylinder head, be careful to not pinch the rubber o-ring imbeded into the head. All you need is to raise this side about 1/4 inch. Now you have enough room to work your fingers better under there from above and you have enough clearance to allow for removal of the screw. Without getting this extra 1/4 inch I could not remove this screw as it back up against the engine while still needing about one complete revolution for removal. Putting the srap and mounting screw back on was a challenge but fortunately the screw doesn't need to be very tightend down (torqued to 7ft/lbs). Remove wedge and tightend (torque) the plenum mounting bolts, make final hose and electrical connection for purge valve and good to go.

Like I said above evertyning but this one screw was cake.

It's been three fill ups, and no more coughing...!