XC90 V8 Vacuum Tank Replacement

The Volvo B8444S engine is an advanced 60° wide-bore short-stroke V8 engine, with a 94mm bore and a 79.5mm stroke (over-square engine). This lends to a rather high-revving nature with peak power output much later in the RPM range. In fact, Volvo rates the engine making it’s peak power of 315hp at 5850RPM and peak torque of 325 lb-ft at 3900RPM. The short stroke, coupled with the close ratio 6 speed TF-80SC automatic transmission make for a very spirited and sporty feel in the rather large and heavy XC90 that tips the scales at over 4400lb.

To give the engine a wider powerband and improve engine response when it’s not running at it’s optimal RPM, the engine is fitted with variable intake runners, with plates that open and close in the intake manifold based on engine vacuum and computer controlled with a solenoid.

Recently while checking over the engine, I heard a loud hissing noise coming from the passenger side (US market, LHD) of the engine towards the cylinder bank facing the firewall. After pulling off the plastic valvetrain cover, I found a mysterious black tank with two vacuum lines running to it – one of the lines had the nipple broken off, and the vacuum was sucking away with a great deal of noise into the vacuum tank. You can see it in the picture below, the black cylindrical tank with the broken nipple on it. I taped up the broken connection to prevent a vacuum leak.

Here is an exploded parts diagram of the vacuum tank. It is labeled as #6 in this diagram:

When you get the part, you get the metal bracket and the tank. The solenoid is a separate part. Here’s what it looks like from the parts supplier. Country of origin is Japan:

Installing the part is actually much easier than it looks:

  1. Remove upper engine mount. This is the piece that looks like a strut bar. Remove the two bolts on each strut tower, then remove the bolt and flange nut on the upper engine mount. Lift the entire assembly off the strut towers. It’s rather heavy.
  2. Remove the rear (firewall side) decorative valve cover. No fasteners on this one.
  3. Spray down the hose connections with a light lubricant, such as WD-40 or PB Blaster. This helps to loosen the hoses on the nipples so they come off easier and save you the trouble of possibly breaking more nipples on more fittings.
  4. Remove the orange clip to the solenoid. This has to be removed so you can access the two bolts that fasten the bracket to the engine block.
  5. Carefully remove the hoses from the vacuum tank. Take your time and try to twist them a bit before yanking them to prevent breaking more fittings. For the nipple that broke off inside the hose, you can just get a new vacuum line from Autozone or do what I did and spray down the inside of the hose a bit with the lubricant and then get a small screwdriver and pry it out.
  6. Remove the solenoid from the bracket. You need to do this because the lower bolt for the bracket is blocked by the solenoid. It is bolted in by a very small bolt on the back facing the firewall.
  7. Remove the bracket from the engine block. Two bolts, very straightforward.
  8. Once the bracket and the tank are out, swap, and re-install. If needed, lube the nipples on the new tank and on the solenoid to help the hoses go on easier. The tank is also a one-way check valve, and the hoses has yellow and white paint to match the connections on the tank. Make sure you put them on in the right location!
  9. That’s it. You’re done. Total time for me was about 20 minutes.




Did you find any of the information useful? Have I helped you save a bit of money / time / frustration? I've spent a lot of time taking pictures and meticulously documenting everything to post it here. I'd really appreciate it if you could send me some money via Paypal! This helps defray the cost of running this website and also provides me with beer to continue writing these articles. Thanks!


  1. will this or pcv valve cause a code for idle too low ?
    my 2006 xc90 v8 when in drive or reverse with foot on the brake car wants to go. shifting to nuetral idle jumps to 1200 and 3 seconds later drops to 650 normal put into drive and car wants to take off . it seems like the choke is stuck in high rpm when car is in gear. I would realy appreciate some input you may have about my problem.

    thank you

    1. Thank you for taking the time to put this valuable info out here. However I’m still getting a lout hissing sound even though I see no hose loose or broken off as in your situation. The sound is so so clear it as if I should see where it’s coming from. Any other suggestions?

      Thanks a million.

  2. I have the exact same problem as Baruk. Just had the transmission overhauled and have a vibration at idle with car in drive and foot on brake. Getting a 506 code, but it feels like a high rpm issue, somewhat akin to brake torquing. Anyone got a suggestion?

  3. My 2005 Volvo xc90 v8 4.4 Yamah, I need some information as to what to expect at 236,000miles, runs great no major problems.

  4. Today I had a very short and quick steam explosion come from the bonnet in this area while driving, and have had a weird morse code coming from it, I recorded a video on it here: https://youtu.be/v_Q940Ys6f8

    Would you know if I need to replace this or if its possibly something else near it?

Leave a Reply

Your email address will not be published. Required fields are marked *