I'm looking for a (small) evaporative emission control system leak (Code PO442). I'm am idiot but where am I looking? Any guidance appreciated! Car runs fine. Just that idiot CEL comes on.

bruce

I'm having the same problem....It seems to throw the code about once every week. I T-eed into the line that runs from the charcoal canister back to the gas tank, and hooked a vacuum guage to it I could monitor from inside the cabin. It appears that whenever my car is running, it keeps the gas tank under a slight vacuum (by slight, I mean the needle doesn't move much away from zero (less than an inch of mercury)). As another test, I filled up the gas tank super full. Then I hooked a hand vacuum pump up to this same T-eed line. Once I built up about 1-2" Hg of vacuum, I could hear a bubbling in the tank as air reentered the tank somehow. The bubbles sounded like they were coming from where the fill spout vent lines connect to the main gas tank. I'm not sure if this is intended or not. Maybe some kind of vacuum relief so the tank doesn't implode if full engine vacuum is applied? The air is not coming in from the cap, and the cap o-ring is in good shape. Anyway, I'm not sure how this system even works, what numbers I should be getting, or the correct way to diagnose it. Thanks in advance for any help! Sorry I couldn't be of more help, Bruce!

Jason
94 850 turbo wagon, 203k
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Jason S. '94 850 turbo 203k

Thanks for your imput Jason! I hadn't thought of hooking up a vac gauge. I think my gas cap is OK or at least it seems tight. I did some searching last night under EVAP and came up with this:

http://www.brickboard.com/AWD/index.htm?id=778874

although most of what I found relates to the A/C evaporator. This EVAP purge valve or the vac lines leading to it may be our problem. I'll try to look at it tonite but is so hot here in the east I may put it off. Many thanks again!

bruce

Bruce...

check out this posting:

http://www.brickboard.com/AWD/index.htm?id=822649

Jason

Any new happenings? The other day, I was getting ready for a trip, and was listening closely to my car, and I heard a hissing. It turned out to be coming from an extra nozzle on the top of the EVAP charcoal canister. I'm guessing the EVAP system was in a purge cycle? I hadn't heard this recently, and I'm pretty observent, so I wonder if it straightened itself out? In addition, now when I crack my gas cap, i hear a bunch of air rush in. I'd like to maybe hook up a vacuum guage and see what kind of vacuum is in the system, but at the same time curiosity killed the cat and maybe I should just let well enough alone. I haven't gotten a single code code in the past two weeks, and I've driven about 1500 miles. Unfortunatley, I didn't do anything to actually "fix" the unknown problem, just did some probing to try to figure out how the system works (which is still unclear). Another mystery is raised by the hissing noise...where does it get this air supply which is above atmospheric pressure? I have a turbo, but normally the turbo is not pumping (especially when its just idling in the driveway), so the intake is under vacuum. I wonder if it somehow creates a pressure using a venturi with vacuum flow or somthing crazy like that???

Jason S
'84 850 Turbo, 205k