Boost rise then fall

[LeeT5]

I deleted it myself as i then noticed that the hose the valve was on went onto your inlet manifold which was removed.

Not a very clear indication, however congratulations for reading it as that is why it was there....lol

What on earth does that mean??

It's a perfectly clear indication of where the valves are on a P2 T5 or P2 R model. It's also totally obvious the inlet manifold is not present, so I'm really not a clue what your on about?

[jdavis]

does anyone have part numbers for these for an 850 please? description sounds like mine need renewing

[Bigsi15]

[Bigsi15]

Finally got a video up! Boost rises then falls back off then picks up a little again. Seems to reach different max pressures each time too. Will try the vacuum valves as soon as possible first

[jdavis]

Yeah mines does that occasionally.

[LeeT5]

Finally got a video up! Boost rises then falls back off then picks up a little again. Seems to reach different max pressures each time too. Will try the vacuum valves as soon as possible first

Looking at the video reminds me of when I had similar boost issues.

Some questions, if I may....

1. Have you had the codes read on the car and what are they?
2. When you accelerate hard and the boost does what it does in the video, if you come to a stop...does the car feel like it's going to stall slightly? Rather, do the revs 'DIP' below normal idle speed??
3. Are you using PTFE tubing anywhere from the vacuum side to the boost gauge?

If the answer to Q2 or Q3 is yes, then you almost certainly have a boost leak post MAF.
If you have a split in the PTFE tube then it will give the symptoms shown in the video. (check this using a MITYVAC)

Likely places for your boost leak will be:

MAF to Turbo pipe (very common and easy to spot - look for oil residue)
Split PTFE pipe to boost gauge
Inlet manifold gasket
Vac tree and associated rubber tubing/vac lines
Split IC
Compressor Bypass valve (spring weakens and rubber deteriorates with age)
Leaking Boost pressure sensor (uses a very small 'O' ring)

On visual inspection....any misty, oily residue around these areas indicates a boost leak.
Some leaks can be almost impossible to detect visually, which is why it's highly recommended to have your car smoke leak tested.

When I had mine done it revealed 4 boost leaks!!! 2 of which, I would have never found. The 5th remaining leak I found once I purchased a Mityvac, because the vacuum hose to the boost gauge was only leaking above 10 psi, therefore, not detected on the smoke leak test.

A smoke leak test will save you a lot of time and potentially money trying to diagnose a boost leak.

All main dealers have smoke leak test machines.

[Bigsi15]

Thanks leet5 this is very helpful and food for thought. I wouldn't be surprised if I have a boost leak somewhere tbh. Il try the vacuum check valves and give it a good look over.

I don't recall any issues with idle or revs dropping too low, codes were clear last time I checked and I'm not sure what ptfe tubing is lol but both the Volvo stock gauge and aftermarket gauge both show the same thing, as far as vac lines go they are almost all pretty new and seem in good shape other than the ones with those check valves in interestingly... Anyone know a good source for good vac lines for these cars and sizings? Might just do them all anyway

Thanks again