Strange PCV / oil trap /crankcase breather cyling s80 2.9

superpudu · Post by **superpudu** » 21 May 2012, 10:00

Hi All,

Great Forum Here; I have been reading for some time but this is my first post. Now the issues...2003 Volvo s80 2.9l N/A 125k miles.

I noticed an oil leak, coming from the top of the motor which got me thinking about possibly having a plugged PCV system, so I began to investigate. My question is about the PCV system. Ever since I bought the car ~30k miles ago there has been a "cycling" of something in the engine compartment. Something clicks on and runs for a couple minutes, then clicks off for a couple minutes. I presumed this was the A/C compressor which is a common complaint, however it occurs with the A/C on or off, summer or winter. Every time this component cycles it changes the idle of the car slightly (when it is on, the car idles slightly more roughly).

I found a clue this weekend! When testing the PCV system, i had the oil dipstick out with the engine idling. Every time the component clicks on, the crank case vacuume dissapears. Then, after a minute or so, it clicks off and the crank case vacuum re-appears! bizarre behaviour to say the least. If the cycling is the A/c Compressor, why would it affect crank case vacuum or pcv operation? My test was placing thin plastic tightly over the oil dipstick tube. Vacuum was easily seen by the plastic being sucked into the tube, crank case pressure was seen by the plastic bowing away from the tube.

Does anyone know how the PCV system is controlled? Is something telling it to cycle on and off? Does anybody have similar symptoms? I am at somewhat of a loss here. I know it sounds crazy.

Vehicle history:
The car runs great, idles properly, good gas mileage and the oil leak is new. Each time this component/relay/solenoid whatever it is turns on the idle speed does not change, only the smoothness/sound changes ever so slightly. Timing belt service done at 100k, including tensioner, water pump, belt, front main seal, thermostat, serpentine belt.

I would most appreciate any help! I am probably going to do the PCV rebuild with the kit from IPDUSA anyways since I have 125k miles, but it would be nice to know what is going on here. BTW just completed a total suspension rebuild so if anybody would like advice/do's and don'ts feel free to PM me.

-Tim

Post by **boosted5cyl** » 25 May 2012, 12:36

Vacuum pump?

superpudu · Post by **superpudu** » 29 May 2012, 08:35

Thanks for the reply Boosted5cyl. I'm sorry for the delayed response; I have been out of town for a wedding. Are you referring to the vacuume pump used to augment the power brakes when the engine is off? That is the only vacuum pump I am aware of; If I am missing one that would explain alot. Thanks - Tim

Post by **boosted5cyl** » 30 May 2012, 18:32

Yeah thats the one. Frankly not even sure if the T6 has one, but its the only "valve" that I can think of in the PCV system. Other than some non-return vacuum valves.

Post by **boosted5cyl** » 30 May 2012, 18:53

Yeah thats the one. Frankly not even sure if the T6 has one, but its the only "valve" that I can think of in the PCV system. Other than some non-return vacuum valves.

superpudu · Post by **superpudu** » 01 Jun 2012, 14:22

I did test that vacuum pump by turning the key to accessory and pressing the brakes. The pump would turn on when the pedal was pressed and turn off when the pedal was released, so I think it is working properly. Since I was only one person I wasn't bale to see what this pump was doing with the engine running however. I am aware that somewhere in the PCV system there is a diaphram that regulates crank case vacuum. I recall reading threads where people would have excess vacuum which would cause whistling through the cam seals if this diaphram were ruptured. perhaps this is related to my situation? I will be going camping tonight, and returning saturday. I am going to try to do some more testing/listening on saturday or sunday and will hopefully be able to provide more information after that. Thanks.