Volvo: Check engine light on a 98 V70 X-C, purge valve, vent lines

Question
Ray,
I have a "check engine" light on my '98 V70 X-C that has been on for many
months now.  I've had it checked by my local trusted mechanic and also the
dealer but neither can find the source of an apparent emission system leak.  
The dealer did a "smoke test" but couldn't find any escaping smoke.  The local
mechanic changed a purge valve of some kind, but that also didn't work.  Any
ideas?
Thanks,
Paul

Answer
Paul,
I do not know what code you are refering to. Smoke test the fuel tank system maybe? I have seen bad vacuum lines, fuel pumps, vent lines from the top of the tank, roll over valve, fuel tanks. Those are the most common. I do know that some of those leaks are very tough to diagnosis. They may not be spending enough time testing for leaks. Go to a shop that works on Volvo and ask about your problem and see if they might be willing to pressure/smoke test the system and spend some time with it. If the system sees a fault, all times that I have had one, there is a leak.