Hello guys. I posted a thread about low boost and after that i did boost leak test. I am hitting only 8-9 psi boost and the car is stock. While doing boost leak, there was not significant boost leak and it pressurized to 16-17 psi and there was not significant boost leak. Now i am wondering could it be related with fuel system? At idle, fuel gauge shows 38-42 psi but while boosting, it does not pass 47-48 psi and i can not pass 80-90 mph. I suspect also fuel pressure regulator and wastegate actuator. By the way, there is not any black smoke . Could the faulty actuator or fuel pump can cause pressure drop like 10 psi (if the stock boost is 17-18 psi)? I do not know where to start and if needed, how to check them. I am waiting for your replies.

 

Catalytic converter broken internally?

Remove it and drive car. It will be loud, but you should know right away if it fixes it. Yes you'll get a check engine light for the rear O2 being disconnected, just clear code when you get the cat back in.

 

Not enough hot exhaust gas to run the turbine could reduce boost output, but I doubt fuel pressure is the problem. If you were really running out of fuel, the pressure would drop substantially and you would experience misfires from the lean condition it would create.
I'd take a good look at the waste gate and the pressure line to it. If you have a boost controller, try taking it out of the system and test drive it once to see if it helped. If none of this helps, then pull that catalyst.
How about the waste gate actuator rod? Does it have much play in it at the turbo? Unrelated car, but similar problem; VW GTI's and Audi A4 2.0t's have the same type issue, from the turbo waste gate actuator rod. It was not sealing up and would allow boost pressure to leak out, right inside the turbo.

 

Does the OP's car have a high mileage Cat on it? I would say let's tinker with the WG. I am assuming original high mileage WG.

Is this like an Evo III, or, IV? Yes....fun

Hint: When new, this car had a 8-10 PSI MHI actuator on it. But that was in 2001. So, let's jump forward 15 years and God knows how many kilometers, how much heat and how many work cycles on that waste gate actuator. Nothing lasts forever. Duh.

 

Thats a good point but i couldn find the symptoms on my car for faulty catalytic converter. I mean can it affect the top speed of car(car is not passing 90 mph).Is it diffucult to remove? And i assume catalytic converter is pretty expensive. Can it be repaired or i will need to replace it?

 

But if there is misfires, there should be also black smoke. Thats why i am not sure about fuel system. Indeed, car is running rich but there is not black smoke or any symptoms to prove it. I will do boost leak test again to check the actuator rod. But could it be actuator itself? I do not know how to check the wastegate actuator.

 

It has 120000 miles on it and i am also suspicious about wga. But i need to check wga before replacing it. And there is something that wastegate actuator must be close at least to 11 psi but my car is just hitting 8-9 psi.

 

A broken cat will cause excessive back pressure in the exhaust which in turn will prevent the turbo from being able to build boost.

I suggested it due to the lack of information giving other than car having low boost and is stock.

It is very easy to remove. However, if you don't know how to remove your catalytic converter, maybe you should take the car to a shop for diag.