Clogged Catalytic Converter??? How to check

DallasDub94 · Jul 3, 2018

Edit* So not the downpipe, but more likely the exhaust manifold. Will update when solved.

I currently have a cobb catted downpipe on my car and I believe the cat is partially clogged. Had a bad boost leak last year and ran rich for quite a while. January of this year I got several stuck injectors while troubleshooting the boost leak (long story), fuel flooded the engine and I'm guessing ruined the cat. It's been fixed, but car doesn't have the pep it used to.

Current symptoms are:

Torque/power loss (not making peak torque till late in the power band)
Car feels sluggish and surgy down low
0-60 time is trash
Engine temps stay high
Lacks acceleration.
Exhaust sounds muffled
LTFT stay rich
Occasional rattle on start
Going up steep inclines I can feel the car struggling
MAF flow is less than I think it should be, ported stock turbo barely getting 200-215 g/s. @ 22+ lbs of boost

Reason I say partially clogged is because I still make full boost. Seems to open up after about 3k-4k rpm.

What would be the easiest way to confirm this short of pulling the downpipe all the way off the car?

Appreciate any advice.

thatspsychotic · Jul 3, 2018

Stock-GTI said:
Current symptoms are:

Torque/power loss (not making peak torque till late in the power band)
Car feels sluggish and surgy down low
0-60 time is trash
Engine temps stay high
Lacks acceleration.
Exhaust sounds muffled
LTFT stay rich
Occasional rattle on start
Going up steep inclines I can feel the car struggling
MAF flow is less than I think it should be, ported stock turbo barely getting 200-215 g/s. @ 22+ lbs of boost

Reason I say partially clogged is because I still make full boost. Seems to open up after about 3k-4k rpm.

What would be the easiest way to confirm this short of pulling the downpipe all the way off the car?

Appreciate any advice.

Have you replaced your PCV? Honestly some of that sounds like a failed PCV valve. My car felt very similar to how you describe when my rear main seal failed due to failed PCV.

My theory on that is that the failed PCV presents a path from the intake manifold to the turbo compressor inlet by way of the crankcase. This makes it feel like a boost leak that doesn't actually throw MAF or too rich codes. And the extra volume in the crankcase that becomes pressurized by boost is additional volume that needs to be pressurized, as well as a boost leak, could also cause the weirdness in the lower RPMs.

I would think that a blocked cat would be less of an issue at lower RPM and more of an issue at high RPM, and I would have thought that the cat would get so hot that it could burn off pretty much anything. Who knows.

DallasDub94 · Jul 3, 2018

thatspsychotic said:
Have you replaced your PCV? Honestly some of that sounds like a failed PCV valve. My car felt very similar to how you describe when my rear main seal failed due to failed PCV.

My theory on that is that the failed PCV presents a path from the intake manifold to the turbo compressor inlet by way of the crankcase. This makes it feel like a boost leak that doesn't actually throw MAF or too rich codes. And the extra volume in the crankcase that becomes pressurized by boost is additional volume that needs to be pressurized, as well as a boost leak, could also cause the weirdness in the lower RPMs.

I would think that a blocked cat would be less of an issue at lower RPM and more of an issue at high RPM, and I would have thought that the cat would get so hot that it could burn off pretty much anything. Who knows.

Pcv got changed to latest revision last year. Turbo spools but slower than it should. I can hear a rattle from the downpipe area when driving at low speeds right after starting the car when cold. Found a thread on audizine with almost the exact same symptoms. Both his turbo and cat were shot.

nevekd128 · Jul 3, 2018

Stock-GTI said:
Pcv got changed to latest revision last year. Turbo spools but slower than it should. I can hear a rattle from the downpipe area when driving at low speeds right after starting the car when cold. Found a thread on audizine with almost the exact same symptoms. Both his turbo and cat were shot.

probably have a broken exhaust stud/leaking exhaust manifold

DallasDub94 · Jul 3, 2018

nevekd128 said:
probably have a broken exhaust stud/leaking exhaust manifold

I was thinking of that as a possibility or in combination with the cat going bad. There is a piercing whistle noise at moderate throttle. Sounds like a fizzle at full throttle. Doesn't always happen.

Do you think I could tell if it's the cat by dropping the midpipe and looking with a flashlight?

DallasDub94 · Jul 4, 2018

nevekd128 said:
probably have a broken exhaust stud/leaking exhaust manifold

I think you are right exhaust manifold leak or broken stud would make the most sense. Hopefully just a bad gasket, stud replacement ain't cheap.

zef · Jul 4, 2018

Beat the crap out of the car, park it and look underneath. If the cat is glowing red, it's clogged.

DallasDub94 · Jul 4, 2018

zef said:
Beat the crap out of the car, park it and look underneath. If the cat is glowing red, it's clogged.

So I'm guessing it's the exhaust manifold leaking. Because I just beat the mess out the car and the cat isn't glowing. Plus I doubt I could hit 24 psi and 140mph with it clogged. Plus just loaded a tune with more boost and hissing/whistling got louder.

BudgetPhoenix · Jul 5, 2018

I'm curious about those other issues you have though if it was just an exhaust leak. I've dealt with multiple downpipe leaks, turbo gasket leaks and only got the occasional p2096 code along with exhaust smell and some extra noise like chirping and hissing.

DallasDub94 · Jul 5, 2018

BudgetPhoenix said:
I'm curious about those other issues you have though if it was just an exhaust leak. I've dealt with multiple downpipe leaks, turbo gasket leaks and only got the occasional p2096 code along with exhaust smell and some extra noise like chirping and hissing.

Car is going into shop to check gaskets tomorrow morning. I'm guessing it's not just the leak causing the performance issue, car is still in the process of being tuned. Got a update last night w/ more boost improved acceleration, about topped out now @ 25 psi. Hissing and whistling under load got louder, occasionally hear the chirping. I partially attribute the engine temps to Texas heat and the amount of boost I'm pushing. Gonna put turbo blanket back on, now that I'm happy with wastegate setting. I think I lost some low end torque due to IE Intake manifold.

I'll update with findings tomorrow.

thatspsychotic · Jul 5, 2018

Stock-GTI said:
So I'm guessing it's the exhaust manifold leaking. Because I just beat the mess out the car and the cat isn't glowing. Plus I doubt I could hit 24 psi and 140mph with it clogged. Plus just loaded a tune with more boost and hissing/whistling got louder.

Ah trip to Mexico I see

DallasDub94 · Jul 5, 2018

thatspsychotic said:
Ah trip to Mexico I see

Well I do live in Texas so it's not that far away lol. Did another long pull today hit 150 going into 6th gear and still had some pull left. I wonder how long my turbo is last at current boost level, glad I have a spare sitting my garage. Need to port it though.

DallasDub94 · Jul 6, 2018

Well shop said no evidence of leak, I'm guessing I'll end up have to dropping the turbo and change the gasket just to be sure. Has to be the exhaust manifold. Downpipe checked out. The hissing and whistling only manifest under moderate to heavy boost and the car runs rich.

Gonna pull the pcv off first and check and reinstall. But car idles fine. No noises at idle.

On another note got tyrolsport caliper kit and stainless lines installed along with motul 5.1. Car brakes a lot better.

zef · Jul 8, 2018

Stock-GTI said:
Car is going into shop to check gaskets tomorrow morning. I'm guessing it's not just the leak causing the performance issue, car is still in the process of being tuned. Got a update last night w/ more boost improved acceleration, about topped out now @ 25 psi. Hissing and whistling under load got louder, occasionally hear the chirping. I partially attribute the engine temps to Texas heat and the amount of boost I'm pushing. Gonna put turbo blanket back on, now that I'm happy with wastegate setting. I think I lost some low end torque due to IE Intake manifold.

I'll update with findings tomorrow.

25psi? Did you go to a 3bar map sensor? Still on the stock map and considering swapping out for a 3. Boost is always safer than timing for more power.

DallasDub94 · Jul 8, 2018

zef said:
25psi? Did you go to a 3bar map sensor? Still on the stock map and considering swapping out for a 3. Boost is always safer than timing for more power.

I have a 3-bar sitting on my desk. I asked the tuner about it, he never gave a definite answer about wanting me to put it on the car. I'll email him today and ask again, not gonna submit logs for a another revision until I figure out where this leak is. Yeah seems like my tuner wants to chase down as much boost as possible rather than timing.

Yeah 25 psi, at least that's what my logs say. Ported ihi w/ forge wga and every bolt on possible. Probably making a little extra because it's trying to compensate for the exhaust leak, idk.

I don't think it's a broken stud. But it most likely is the exhaust manifold gasket, gonna tighten the bolts first and if that doesn't fix drop the turbo and change the gasket/bolts. If it's still there after than idk.

Clogged Catalytic Converter??? How to check

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