BOOSTD

My car has been limited to 5-7psi. It struggles to even get there so I don't go WOT to see if it will build more boost. I've replaced the N75 solenoid, MAP sensor, checked turbo and all vac lines, new MAF is ~4 months old. VAGcom shows requested boost as normal, actual reflects what my boost gauge says (5-7psi). Over a year ago I had a ceramic core cat die on me, and when it was pulled out there were chunks of the core lodged in the cat housing. I'm sure some of it went downstream but it has never caused a problem.

This weekend I put the car on a lift and disconnected the downpipe from the rest of the exhaust, and used bailing wire to support the downpipe. When I test drove it with just the downpipe for an exhaust the car reached peak boost again although boost built slower than normal. It has been suggested that this is to be expected on a 1.8T running without an exhaust, because they do require some backpressure to spool up. Loss of low-end torque in exchange for freer breathing up top. Does this sound correct? Has anyone run a 1.8T with downpipe only/no exhaust for testing purposes like this? What was the result?

Right now the theory is after months of no problems the ceramic cat core is somehow now lodged in the exhaust, or part of the baffle system has come apart causing a blockage.

WYSIWYG

umm where's your snake during the symptoms?

RAD69

Fast back to the original psi or drops lower than it did before the test pipe came loose?

WYSIWYG

drops lower than normal boost level

RAD69

Hmmm... I wonder why?

skabaru

and while it was MUCH louder, there were normal boost levels, but as you found, a bit longer to get up there... so exactly as you stated, loss of low end, but better high end...

I had just thrown in a new cat at the time, so I can't comment that well on high end, but my finds roughly match yours.

you have the stock APR exhaust right? is that welded, clamped, or flanged? can you pull it and shake it? have you tried using a wire snake or a plumbers snake to poke around in there? I would imagine any cat contents would have gone into the center resonator...

How loud do you want to be? I am running no center resonator... just pull it out!

BOOSTD

Dealer service dept. let me use one of their lifts late Saturday afternoon (hehehe) so I didn't physically remove the center section, just disconnected the joint and wired it up to keep them from dragging for a quick test run. When I remove it I'll be inspecting it for chunks of ceramic and/or broken baffles.

SameerP

Perhaps it might be a crimp in the IC setup?

The symptoms you describe sound just like heat soak tendencies...5-7 psi, sluggish. If you've opened the exhaust up to just the DP and you are not running like before, perhaps its an intake, not an exhaust issue?

Maybe with only the DP you are managing to see normal-ish boost because it flowing so well compared to the exhaust, that it's masking the issues a touch?

Just guessing here...

Cheers,
Sameer

LaserK04

If the exhaust was blocked, I'd assume it would get considerably quieter, or at least you'd notice a drastic change in the tone.

You mentioned a slower spool-up with no exhaust, which seems odd. The more I free up my exhaust, the faster it spools. Quite contrary to your experience, but you are Stage 3, no?

When the old cat went bad did you replace it with another or use a test pipe?

Does APR use striaght-thru mufflers like Borla? If so, use an electrician's fish tape and force it thru the piping to check for blockage.

If the performace came back when you removed the exhaust, clearly, that's your problem. I'm amazed that if it was that blocked, that the tone of the system didn't change enough for you to notice.