|
So I used this thread to fix the howling in my new to me 2002 boxster. The previous owner put tape in the fuel vent. It didn’t come up during inspection but once I found it when I tried to fill up with gas I knew what was going on. The symptoms were a howl that was intermittent under a variety of conditions from idle to steady cruising at 3000 rpm in 2nd and 3rd gear.
My first step was to replaced the two valves F and G and tried to blow out line E. The result was it made that howling worse. With the engine running and howling, I disconnected E and could feel the vacuum pulsing and eventually the vacuum became constant. This made me think that possibly the solenoid valve on the manifold was sticking. I made sure to clean out the housing for F and G.
I then replaced the solenoid valve 15. This definitely quieted down the howling. It was softer, would still occur at 3000 rpm but would stop on a regular interval.
I figured since vacuum followed a path of least resistance that maybe there was too much vacuum in the evap system possibly due to a plug in the charcoal canister or maybe the filler neck valve was malfunctioning. So got those parts on order. I also ordered a CO2 drain gun because it has a nice rubber cone that seals against hose orifices for blowing them out.
Ok round 2 with F and G. I figured maybe I didn’t blow out E good enough the first time. I had hunted up the parts diagram for line E. It takes a very circuitous path through the car following the fuel line past the engine to the rear bumper. Lots of things could get stuck in that line, how I don’t know but certainly a spider nest or something could also plug the end. I used the drain gun to blow out line E. The first couple of shots, there was a fair amount of back pressure but with the 3rd shot there was a major reduction in back pressure. The fourth shot could be emptied into the line with little blowback. Ok maybe I cleared something out. Here is the diagram for the path taken by E.
https://einmaligparts.3dcartstores.com/Fuel-system-201-05_c_7839.html
Line E is item 6 in the diagram.
After a series of very lengthy test drives the howling seemed to be mostly gone. I did have an intermittent how for a second or two but that would be it. It would occur at speed typically 3000 rpm.
So the charcoal canister and filler neck arrived this week. I decided I would go ahead and install them because the car was pretty old and by this time I’d renewed almost the entire EVAP system. First part to go in was the charcoal canister. The old canister was the same part number as the new one but the old canister weighed about a pound more than the old one. Maybe it was partially plugged and reduced the overall effective capacity of the evap system which I presume operates on a fixed vacuum so the total volume being evacuated could be reduced leading to some excess vacuum through E. Ok also replaced the filler neck valve in this session. I realize up until this point I was doing pretty good science changing only one thing at a time but I’m sick of taking my car apart. The old filler neck looked quite work, the plastic was dull, but blowing through the holes it seemed to operate like the new one. I’ve read that there can be cracks in these valves. The gas cap puts strain on the filler neck and people sometimes crank down on their gas cap. Swapped out the filler neck. Oh and I blew out E a few more times since I had the whole fender liner out.
Went for a test drive. Nothing, no sound. I think I got it fixed. The evap system is quite a Rube Goldberg. I’ll point out that the system in the 987/997 is much simpler and no one complains of any howling in those models.
I know some people put tape over the vent. This does stop the howling. Surprisingly since the bowl is caused by a vacuum leak there is no check engine light. Since the leak occurs at a part of the system that isn’t monitored, the fresh air leaks through F and D instead of the correct fresh air source E. I think I had a couple of parts that had failed or were failing. I wonder if putting tape over the vent hole causes some longer term damage to the solenoid valves since their springs are being worked by the excess vacuum making the whole system leak more. This may eventually produce a check engine light but not for a while it seems.
I couldn’t live with the tape. I would forget to remove it when pumping gas and then gas would backup all over the filler. I also replaced the gas cap with a genuine Porsche gas cap. The old one was an aftermarket. Replacing the gas cap did nothing btw.
Biggest thing I learned is the drain gun is a handy tool for blowing out the lines because it allows you to use a fixed charge of co2 and feel the change in back pressure.
|