Loss of Power / Boost - Twin Turbo

[Sue-Baru]

Hey guys,

 

Im trying to sell my 98 GTB TT Legacy wagon as I've upgraded to a 2007 Legacy.

Before I sell the 98, I have a few things to fix up first (CV boots, rocker cover gasket, loss of power / boost)

 

Im trying to figure out why the cars loosing power. It happens most noticeably up long hills (passing lanes up hills). The car will be running fine with lots of power but on long hills the car can slow to a crawl. It seems to happen when the second turbo kicks in around 3500 - 4000 rpm. If I pull over or drive slow for a bit the power seems to come back again.

 

It also happens occasionally on the flat too and just feels like the second turbo isnt there.

 

Does anyone know what it can be? BPV? Vacuum leak? Wastegate sticking? Clogged cat?

 

As far as I know the engine has no mods

  

Edited May 22, 2017 by Sue-Baru

[Marky]

You're not talking about the normal loss they have between the turbo switchover are you?

 

Does it ever bring up a check engine light?

 

Do you have a boost gauge on the car? 

[Sue-Baru]

2 hours ago, Marky said:

You're not talking about the normal loss they have between the turbo switchover are you?

 

Does it ever bring up a check engine light?

 

Do you have a boost gauge on the car? 

I dont think so, but come to think of it it wont rev past 5000 rpm because theres no power.

 

CEL has come up once after a long passing bay.

 

I dont have a boost gauge.

[Marky]

It sounds like an issue with either the second turbo, or the switchover mechanisms from single to twin - if one of the valves is opening when it should or shouldn't then that will do it, ditto if the second turbo is just kaput

 

Could be the exhaust valve stuck closed

Could be the intercooler valve stuck closed

Could be the blow off valve from the secondary stuck open or faulty

 

It's hard to nail down from what you describe, but would be relatively quick to rule out those obvious culprits to someone who knows their way around them (a boost reading would help a little too) 

Where in the country are you? 

[Sue-Baru]

24 minutes ago, Marky said:

It sounds like an issue with either the second turbo, or the switchover mechanisms from single to twin - if one of the valves is opening when it should or shouldn't then that will do it, ditto if the second turbo is just kaput

 

Could be the exhaust valve stuck closed

Could be the intercooler valve stuck closed

Could be the blow off valve from the secondary stuck open or faulty

 

It's hard to nail down from what you describe, but would be relatively quick to rule out those obvious culprits to someone who knows their way around them (a boost reading would help a little too) 

Where in the country are you? 

Thanks, ill admit i have limited mechanical knowledge but am willing to give some things a go.

Im in Hawkes Bay. Does anyone know of someone who can diagnose this problem in the area?

 

I would of thought if the second turbo is gone it wouldn't be an intermittent issue??

 

[Marky]

I wasnt sure if the no-past-5000 thing was all the time or intermittent

 

If it's intermittent I'm thinking maybe something sticking open or closed when it shouldn't be

[Sue-Baru]

Yup - so whats the best way to go about diagnosing and fixing the problem?

[Sue-Baru]

The line into the exhaust gas supply control valve has split. Would that cause an issue like this?

https://goo.gl/photos/ZbfkJ8y35NKDVDCcA

[les666]

The line into the exhaust gas supply control valve has split. Would that cause an issue like this?
https://goo.gl/photos/ZbfkJ8y35NKDVDCcA

Yeah it can do. A couple of other things to check are that the exhaust control valve isn't stuck either opened or closed. That the bypass control valve isn't leaking and that the intercooler valve is opening and closing. For the first and last point you could chuck it into diagnostic mode where it cycles the fans and actuators briefly and see if they move.


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