Replaced PCV Diaphragm Weird Noise

cham · Post by **cham** » 09 Apr 2025, 15:12

Have a 2010 XC70 3.2 NA I decided to replace the PCV diaphragm on, and the engine is making a weird noise now. Since the entire oil trap is somewhat expensive, there is a lot of info online of people replacing just the diaphragm and its cap with an aftermarket part. Mine was from amazon for $25. Fit just as the old one did but now when accelerating this weird noise happens generally when you get over 1100 RPMs. I have removed it and reinstalled it a number of times now as well as the original part with no change. The old original diaphragm didn't even seem that bad when I removed it either go figure. The interesting thing is when in park, it makes no such sound when revving the engine above 1100 RPM. I have only heard positive reception surrounding this aftermarket part, so much so FCP Euro sells their own version of it. During installation I did have to unplug one of the cam position sensors that sits right next the pcv diaphragm. I wouldn't think this is a problem.

The only other thing I can think of is when I was replacing it, I had been leaning my hand on the hose that connects to the vacuum pump next to the PCV and it made like a cracking sound and gave way. I think the plastic parts had just been frozen together and now they spin freely but still are connected. As far as I can tell there isn't any damage, it just moves freely now, since it has an o-ring, rotation within its port should not be a problem.

I noticed though (not sure if this is different from before or abnormal) but when shutting off the car, a large whoosh of air purging comes from that location where the vacuum pump is. I need a helper to locate its exact location but in the meantime here is a video of what it sounds like. I'll also provide a video of what the car sounds like accelerating over 1100 RPM while driving. Disregard the rattling, that's just a phone mount.

Steve H · Post by **Steve H** » 25 Apr 2025, 18:33

Pull the oil stick to break the crankcase vacuum and see if the noise stops. If so, something went wrong with your diaphragm install in my opinion.

cham · Post by **cham** » 27 Apr 2025, 10:54

So I ended up replacing the Oil Trap PCV with the full factory part to rule out the aftermarket part installation. No change. I also replaced the plastic valve for the vacuum pump since I did hear that cracking sound when leaning on the hose (its also been leaking oil for a while). No change. There are two o-rings that seal the hose to that plastic valve that look a little worse for wear; maybe I'll try replacing those.

The sound when driving honestly sounds like a vacuum issue and the car behaves like it's a vacuum issue. Maybe something happened leaning on the intake runners while replacing the diaphragm the first time? I'm kind of at a loss at this point and will likely take it to professionals. I've actually sourced that depressurizing sound when shutting off the engine to the plastic intake runner. Maybe something is going on with those intake volume flaps?

Any chance it might have to do with the ecu and it needs to be reset since I unplugged that cam position sensor when replacing the PCV? Again the noise is not made when in Park and revving it.

cham · Post by **cham** » 03 Dec 2025, 15:23

Thought I'd update, took the vehicle to a Volvo specialist a while back and they said it looks like one of the READ bearings is going out and causing the noise. I must have started working on the car and didn't realize the noise was already there to begin with before replacing the PCV trap.

They claim its the bearing on that internal READ gear having too much lateral movement (the one facing the alternator, not the accessory belt side). Super expensive to fix. Now I've read that pulley bolt can come loose and back out causing some of these issues. Sounds like that bolt can back out sometimes because the alternator decoupler/pulley seizes up. Is there anyway to easily tell if the alternator decoupler/pulley is seized and if the READ pulley bolt on that side of the unit is loose?

I should note the car does not struggle to start or hold a charge so I'm guessing the alternator and decoupler is functioning if that is the case? Ironically the sound has gotten better over time not worse.