Intermittent low boost - tuned '06 2.5T
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    1. #1
      Junior Member CDN XC90's Avatar
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      Ottawa, ON, Canada
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      Intermittent low boost - tuned '06 2.5T

      Low mileage (83k kms) 2006 XC90 2.5T AWD. See my build thread for more detail.

      I've been running a stage 2 tune from Contrast since the end of October and it's been solid. A few revisions to fine tune, but overall, I'm very impressed with the newfound power, so much more fun to drive. Can just step on it and it responds. I would highly recommend his tuning expertise for any boosted Volvo.

      However, I have experienced a low boost scenario a couple of times where the engine would not build boost. I have a Speedhut boost gauge mounted in the dash and it's been very interesting to watch the boost come on, from before I was tuned and now. The odd time, when I give it gas now, it will only show 0 boost, comes up from vacuum but doesn't build past that. If I let off the gas and press it again, it will respond as expected again. I tried to capture it in logs for Gustav and he confirmed that he could see it but couldn't ascertain why. It was clear that the request was high and TCV duty cycle was maxxed out. He thought it could be a faulty TCV or a bad connection at the plug. To be clear, I don't think this is a tuning issue at all based on what I've read on the forums. It's possible it might have occurred prior to the tune but I don't recall and the difference in power would have made it much less evident. I can't rule this out as pre-existing but I don't remember it happening either in the 30k kms I've had the vehicle.

      Anyhow, I ordered a new Pierburg TCV from FCP Euro, but didn't install it as the car was running beautifully 95% of the time Then, last Thursday, it happened again, but this time, it didn't correct itself as it always did before. After the reading I had done over various reports of issues with the TCV, it sounded similar to my scenario and that my original was probably on it's way out, with the intermittent issues, but now it had failed. I drove about 25kms after the issue occurred and it didn't recover. If I really left it floored, I would see upwards of 5psi, maybe, more like 3-4psi on the gauge. But basically no boost. So, I swapped out for the new TCV Friday night.

      Saturday afternoon, I took the car for its first drive since and initially it was the same, no power, but then it recovered. Then it did the low boost thing again once more but now, it's been fine since. So I'I was initially disappointed to find that the TCV wasn't the issue but now I'm not sure.

      I'll put more miles on the car over the next few days but wondering what folks think could be the issue if it's not the TCV? Should I be replacing the vacuum lines? Compressor bypass valve spring kit? Would I see anything in VIDA?
      2006 XC90 2.5T AWD - Contrast Works Stage 2 tune with Eco Enhance mode, HEICO Bilsteins and springs, IPD Swaybars, strut brace conversion kit, and subframe bushing inserts. Fast FC05 20x8.5 with 255/45/20 Conti DWS06. Falken HS449 235/65/17 winters. JL 500/1 with Pioneer TS-SWX2502 subwoofer under cargo tray. LED low/hi beams, Tuxmats.

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    3. #2
      Junior Member CDN XC90's Avatar
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      Didn't reoccur in 100kms of driving since I posted above...

      I did take advantage of the current sales to order a Forge CBV upgrade though - https://www.vivaperformance.com/cbv-...urbos-fmdvrmr/ $124 for a serviceable part on sale.

      I'll continue to monitor if/when it reoccurs.
      2006 XC90 2.5T AWD - Contrast Works Stage 2 tune with Eco Enhance mode, HEICO Bilsteins and springs, IPD Swaybars, strut brace conversion kit, and subframe bushing inserts. Fast FC05 20x8.5 with 255/45/20 Conti DWS06. Falken HS449 235/65/17 winters. JL 500/1 with Pioneer TS-SWX2502 subwoofer under cargo tray. LED low/hi beams, Tuxmats.

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