No boost or little boost, volvo s70 t5 850t5 1997

Thegingerwithavolvo · Post by **Thegingerwithavolvo** » 17 Aug 2026, 05:52

Hello there reader!

Again here with a problem (sadly). Before i had a problem which was a faulty 02 sensor, which is now fixed! It was a wire from the chassis which became loose, causing no signal to be send.

However now the car makes 0 boost and sometimes like 8 or 9 psi, which is normally around 18 psi flat out (has computer change).

Context: my car is a volvo s70 from 1997 and has a volvo 850 t5r. There are some small modifications like a bigger intercooler and reverse piping kit, race intake and exhaust. But nothing super weird. After finally finding the 02 problem with holding back my car weirdly it drove fine for 2 weeks, after fixing a faulty BOV spring kit. This caused it to overboost (20psi) a few times. Luckily it seems no damage to the internals or something like that. But 2 days afterwards it just made 0 boost. And after changing the TCV it made like 8psi, at least something but not a lot, also how the boost came on was a lot different. A lot later then it should (4000rpm finally making some boost)

And the garage could not find anything wrong with it mechanically and the chiptuner said it could not be the computer so now I am at a loss.

The car drives fine, no weird things, just slow cause of the lack of boost. No leaks, no broken sensors, no engine code. Nothing! That is what makes it so weird. The turbo was also checked internally and all looked well.

I hope someone can help me since it makes my car alot less fun to drive and i like it alot :*).

So if anyone has this before or has any clues, no matter how small, let me please know!

Kind regards,

The ginger with a volvo

Post by **matthew1** » 17 Aug 2026, 18:31

Intercooler leak at the fittings or cracked intercooler itself? That causes low boost, ask me how I know.

Post by **scot850** » 17 Aug 2026, 20:02

What TCV did you use as the replacement? Volvo standard is only reliable up to around 12psi boost. I suggest first have your intercooler and pipework Smoke tested for leaks which helps look for leaks like Matthew suggests.

Post by **erikv11** » 17 Aug 2026, 22:35

Does the CBV hold vacuum?

Thegingerwithavolvo · Post by **Thegingerwithavolvo** » 19 Aug 2026, 05:01

matthew1 wrote: 17 Aug 2026, 18:31 Intercooler leak at the fittings or cracked intercooler itself? That causes low boost, ask me how I know.

Thanks for the information!

Not checked yet but ill make sure to do so! Luckely the reverse kit from IPD makes it sit on the top (the fittings) towards the turbo. Or are there also other fittings I shouls check with the intercooler that can have such an influence? Same with the cracked intercooler, what is an easy spot to see the whole intercooler/big part? I was thinking simply the front of the car but let me know!

Thegingerwithavolvo · Post by **Thegingerwithavolvo** » 19 Aug 2026, 05:05

scot850 wrote: 17 Aug 2026, 20:02 What TCV did you use as the replacement? Volvo standard is only reliable up to around 12psi boost. I suggest first have your intercooler and pipework Smoke tested for leaks which helps look for leaks like Matthew suggests.

Thanks for the information!

I now have the standard tcv from a volvo s70t5 in it, before that I had one from an MG, which also worked fine (was an recommendedation from another forum on this forum site). Its true that they are not meant for the bigger boost, however mine previously held on for 1.5 years or so with it (somehow). So I should at least expect it to work for a short while rather then just refuse to do higher boost. Any recomendations for a replacement part? I heard the IPD ones are not so well made and a bit of a hit or miss...

The smoke test is a good one, not sure if the garage had checked that system, vacuum system and lines was checked for sure. Where would you recommend to tap in to get into that system?

Thegingerwithavolvo · Post by **Thegingerwithavolvo** » 19 Aug 2026, 05:14

erikv11 wrote: 17 Aug 2026, 22:35 Does the CBV hold vacuum?

Thanks for the idea!

The CBV has been out a few times since that can cause alot of issues and I have a stronger spring in it from IPD. This was to make sure the spring can actually hold the boost and not collapse or do weird things with the boost. Changing it towards a lighter spring has not seemed to help with the low/non boost problem btw....

The rubber seemed not cracked or anything like that and my boost gauges reads -10.8 psi at idle, which it always has done. The actuator was tested with some pressure and also seemed to work fine. Otherwise let me know what you mean/how I can test that!

Cees Klumper · Post by **Cees Klumper** » 20 Aug 2026, 07:09

Besides the smoke test and a visual check of the big hoses to and from the intercooler, if you have even a small air compressor, even a 'fietspomp', you can put some air pressure into the turbo hoses/pipes and then listen for air leaks.
Last year one of the clamps securing one of the big intercooler hoses failed on my C70 T5 which killed the boost. But, it was producing a major air noise. So perhaps this is not your problem.
You could also check the engine ECU for trouble codes ...

Post by **erikv11** » 21 Aug 2026, 09:19

You can test the CBV diaphragm for leaks by pulling off the vacuum line and applying low vacuum with a gauge on the CBV nipple. You need to fashion some kind of rig e.g. a brake bleeder pump or a blood pressure bubble. See if it holds vacuum/pressure. Maybe this is already done from your description?

What has also worked for me is hold the diaphragm up to strong light and look for pinhole leaks but a negative result there is less convincing.

It sounds like your leak may be larger than CBV would explain, given the recent tests you've done with CBV.

Thegingerwithavolvo · Post by **Thegingerwithavolvo** » 22 Aug 2026, 11:30

Found the issue!!!

Hello everyone! I want to say thanks for the great ideas and tips. Well the good news is that I found the issue for cheap, the bad news is that the issue is not cheap hahah.

So a friend and I used a cheap pump, vacuum lines and literal cigarrets to smoke the car for vacuum leaks. Worked great! (If you use a rubber glove to force the air into the system instaid of going out the filter). We had also taken out the front panels to see every clamp and rubber fitting. There where 2 "leaks" (see photo's). One is on the bottom of the intercooler, while the other is at the back of the car, connected to the intake with vacuum line and the other to petrol pressure line. I do have a question, what are they,is it normal and what is it for?

To get to the point, we checked the turbo Turbine again to make sure it was not simply that...well...4 weeks ago i also checked and I found nothing...maybe I was drunk or high as a kite since the play we found was a centimeter or so (3rd of an inch for you americans) so yeah the turbo is cooked. We also saw with a camera line tool some scraping and stuff (see photo) so it was simply that.

Now I have a 850t5-r engine, my question is now: which type of turbo is it normaly? 15G? And is it the coned or straight variant/how can you confirm that? Furthermore which turbo's are plug and play and also do not need a new ECU tune?

Kind regards, Thegingerwiththevolvo