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sean, Technician
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Experience:  Certified Ford Master Technician. Technician since 1984.
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catalytic converter boost gauge never reads positive..smoke

Customer Question

I have no turbo (no boost)... perhaps my pre-turbo catalytic converter went? I didn't notice it gradually go I simply didn't have power one day and my boost gauge never reads positive.  I don't have any smoke or smell coming from my vehicle.  It feels extremely sluggish... even less power than my girlfriends toyota corrola.  Are there any checks I can do myself to determine what the cause is? air leak in a hose or blown cat converter, etc.

I have a 2004 subaru wrx - 120k miles
Submitted: 5 years ago.
Category: Car
Expert:  Michelle-Mod replied 5 years ago.

Hi, I’m a moderator for this topic and I wonder whether you’re still waiting for an answer. If you are, please let me know and I will do my best to find a Professional to assist you right away. If not, feel free to let me know and I will cancel this question for you. Thank you!

Customer: replied 5 years ago.
Yes, I am still waiting for an answer.

Thank you,
Expert:  Dad Mechanic replied 5 years ago.
sorry for your trouble. The caolitc converts are not on the boost side of the turbo. they are after the turbo on the muffler side not the engine side, this is the side of the turbo that drive it. sounds like you may have a rubber hose connecting to the turbo on what is called the charge side of the turbo that has come off or is cracked and you are loosing boost. You could have someone accelerate the engine while you are under the hood listen for rushing air. I hope this has assisted you. Come back to me and let me know if this has helped you. Jim!!! here is a diagram of a later subaru turbo system you could also have a waste gate problem. they also can manifest them selves quit quickly. n-US:official&biw=1024&bih=616&tbm=isch&prmd=imvns&tbnid=MALqjr2e1qiwuM:&imgrefurl=,r:13,s:0,i:101...
Customer: replied 5 years ago.
Relist: Inaccurate answer.
Contrary to what Dad Mechanic says, the vehicle in question, a 2004 Subaru Impreza WRX, does indeed have a pre-turbo or "on the boost side" catalytic converter. His answer 1) wasn't helpful and 2) was inaccurate
Expert:  Dad Mechanic replied 5 years ago.
sorry you feel that way , you are wrong no cat was ever put on the charge air side of any vehicle. cats are to clean exhaust gases before they are released to the atmosphere. you still have a leak either on the waste gate or charge hoses. no i will opt out as you are looking for someone to agree with what you already believe! Jim!!!
Expert:  sean replied 5 years ago.

Hello, as your previous expert opted out I'll try to assist further.

The 2.0L WRX fro 2002 to 2005 has a catalyst before the turbo in the up pipe if this catalyst breaks up which it is prone to doing so then it can cause serious damage to the turbo causing a lack of power. This catalyst isn't fitted on the 2.5L.

Removing the catalyst is as far as most WRX owners are concerned a "must do" for this reason.

As long as no pipe work has split for the pressure side of the turbo including the inter cooler then you need to remove the up pipe and check the catalyst condition and turbo for damage. An example of the type of damage to the turbo is shown below.


The up pipe is a little awkward to remove.Alternatively if you can plumb in a pressure gauge you can check the boost pressure but be careful as if the catalyst has broken up you may cause more damage, from your description it may well be the pre turbo catalyst that has broken up damaged the turbo so giving no boost.

Let me know if I can assist further.

Best wishes,


Customer: replied 5 years ago.

I have just a couple more questions but thank you already for the help. 1) If it is the up-pipe cat that broke apart is there a chance that my turbo isn't catastrophically damaged yet even though I have no boost? 2) Do I run the chance of damaging my vehicle if the up-pipe cat did indeed break apart and the turbo is damaged/ruined... basically if the turbo is already shot can I run the car normally aspirated (sp?) or will this not work due to the ecu, fuel mgmt, etc. (all that stuff I know nothing about)?

Thanks so much,
Expert:  sean replied 5 years ago.

Hello again,

the car will run normally aspirated but I wouldn't as if you do you run the risk of further damage. Obviously if the turbo vanes have been damaged this will cause the turbo to be out of balance which may result in further damage. The thing is if it is only the turbine (in the exhaust side) that is damaged at the moment then no damage should have occurred to the engine, if the turbo fails completely then the compressor end of the turbo can hit the housing causing debris to go in to the engine with catastrophic results.

You need to investigate the lack of boost pressure first, as I said earlier make sure all the intake pipe work is OK and the inter cooler although normally if there is a split you can hear the pressure escape as the turbo starts to boost.

Let me know if I can assist further.

Best regards,


sean, Technician
Category: Car
Satisfied Customers: 3105
Experience: Certified Ford Master Technician. Technician since 1984.
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