Crazy Overboosting

WhatAmIDoing · Post by **WhatAmIDoing** » 18 Apr 2018, 15:52

I have a 1998 S70 T5 5spd. My Volvo has had a problem with over boosting, but I've been keeping it under control with a disciplined right foot. The other day, however, I was having a bit too much fun. I put my foot down in 3rd gear, and by 4500 rpm my boost gauge was reading almost 20 psi. To spec isn't boost suppose to be limited to 12psi on the HPT? 1st gear peaks at about 6psi, 4th gear peaks at 12psi, but 2nd and 3rd are shooting for infinity. So I'm guessing my problems are either: way out of spec wastegate adjustment, bad TCV, or a wonky boost gauge.

I have a Sunpro boost gauge that was installed by the PO. I question whether it's reading correctly, because A) I think at 20psi I would have broken something, B) I have no codes for over boost, and C) can the stock turbo even make 20 pounds of boost?

I never got around to properly adjusting the wastegate as I never got my hands on a pump and pressure gauge. Even if the TCV was bad, it wouldn't overboost this much, right?

Post by **matthew1** » 18 Apr 2018, 17:21

I had 17-18psi going through my 850 HPT for a couple years until I blew the intercooler on a very hot day.

You'd know if it was pushing 20. The indications are the speedo and tach moving clockwise very quickly, and a very pushy feeling in your back.

I don't mean to minimize the inherent danger to the car at 20psi boost. But if you're ok with testing the limits, the worst you can do is blow something and need to get off the road. It's not like testing the limits of failing brakes.

Post by **scot850** » 18 Apr 2018, 17:22

The standard TCv struggles to control past about 12psi. My 00 'R' has a tune, and it runs at 18-20 psi with the 19T turbo.

It does seem strange that the 1st and 4th gears are ok and 2nd and 3rd are not. Cannot think why that would be as I would have had a problem with the wastegate or TCV would affect all gears as they all use pressure or vacuum.

Neil.

WhatAmIDoing · Post by **WhatAmIDoing** » 18 Apr 2018, 21:49

matthew1 wrote: ↑18 Apr 2018, 17:21 I had 17-18psi going through my 850 HPT for a couple years until I blew the intercooler on a very hot day.

You'd know if it was pushing 20. The indications are the speedo and tach moving clockwise very quickly, and a very pushy feeling in your back.

I don't mean to minimize the inherent danger to the car at 20psi boost. But if you're ok with testing the limits, the worst you can do is blow something and need to get off the road. It's not like testing the limits of failing brakes.

I'm all for testing limits, but I would prefer to not ruin a perfectly good engine. She moves pretty good, so I wouldn't be surprised if I am pushing 15psi. But I would prefer to have the peace of mind of keeping boost within spec.

scot850 wrote: ↑18 Apr 2018, 17:22 The standard TCv struggles to control past about 12psi. My 00 'R' has a tune, and it runs at 18-20 psi with the 19T turbo.

It does seem strange that the 1st and 4th gears are ok and 2nd and 3rd are not. Cannot think why that would be as I would have had a problem with the wastegate or TCV would affect all gears as they all use pressure or vacuum.

Neil.

It is weird behavior, as I would have thought it would be the same in all gears. This is honestly really bizarre. Not really sure where to go from here.

Post by **Clemens** » 18 Apr 2018, 23:50

If sou Really Think you are getting 20 psi start with wastegate Adjustment to Factory Settings. In 1st gear boost is Limited by the ecu or TCM. In 4th it might be geared too long for overboost

Post by **abscate** » 19 Apr 2018, 04:31

TheCBV should be opening before you reach that boost level? Check the IPD cbv to see the options there.

WhatAmIDoing · Post by **WhatAmIDoing** » 19 Apr 2018, 09:13

abscate wrote: ↑19 Apr 2018, 04:31 TheCBV should be opening before you reach that boost level? Check the IPD cbv to see the options there.

Are we thinking a previous owner may have modified the turbo? The guy I bought it from was a fan of IPD, but he said nothing about the turbo. I think he said the overboost was being caused by a bad control module. But when I bought it, boost maxed at about 14psi, not 20+.

Post by **wizechatmgr** » 19 Apr 2018, 14:27

CBV likely not connected and/or wastegate misadjusted or plain hooked up wrong.

Post by **abscate** » 19 Apr 2018, 20:22

If the CBV hose is off it will still blow off against the spring if it’s the right one.

I bet he put the red spring In, which is a no no.

Get these parts right before you Bend a rod

WhatAmIDoing · Post by **WhatAmIDoing** » 20 Apr 2018, 01:17

abscate wrote: ↑19 Apr 2018, 20:22 If the CBV hose is off it will still blow off against the spring if it’s the right one.

I bet he put the red spring In, which is a no no.

Get these parts right before you Bend a rod

I agree. How hard is this to pull apart and check/replace?