Catalytic Converter Failure - Breaking up

[Faded95]

I have a 95 tsi-awd with a custom 3" exhaust:
2.5" dp to a 3" flex, 3" cat (AP 608227) and Vibrant Streetpower muffler

I replaced my old magnaflow high flow cat with the one mentioned above in order to pass emissions last summer, since then the first AP 608227 broke up (it sounded like a rock in a tin can) and was warrantied. Now the second AP 60627 cat is vibrating like the first one.

I called AP's tech service line and was told that the usual cause is unburnt fuel igniting in the cat and melting the substrate or very high temps from the exhaust. My EGT's have been relatively normal, 800-1200 so I'm guessing if anything it's leaky injectors. He also told me that the excess heat would cause a purple discoloration; I had the car on a lift today and it looks normal.

If the excess fuel were the case, wouldn't my old magnaflow have had a melted substrate as well (on the car for 2 years)?

My thoughts are this:

1. I also have read that low end ceramic cats don't handle vibrations well - curious if anyone has had issues with this.

2. My car is pushing 17-18psi on a 14b, doesn't seem like much but could this be causing the brick to dis-lodge?

3. Maybe it is the fuel - I'll run some Lucas fuel system cleaner through and replace my fuel filter.

I've got to figure this out quick, my mileage is down, my power is down and the noise is driving me crazy! Any help would be appreciated.

-Ryan

 

[cisco5311]

How does your state do emissions testing?

Here in OH, they just use the OBDII system to check for DTC's and do a visual inspection for a catalytic converter to be "present".

I have a look-a-like converter on my GST, basically a shell of a converter without the honeycomb inside!

 

[Oldsid]

I would say the cause of melting your cat is temperature due most likely to excessive fuel in the exhaust manifold. Are you running rich ? Do you have any misfire? The noise you hear (clinking sound) are pieces of ceramic that have broken off.
As for your EGT as being "normal", I would say it depend on where the probe would be mounted. It may not "see" the high temperature on the cylinder that has excess unburned fuel that can burn after the probe and will not be detected. The only reliable way to see temperature for all cylinders is to have an EGT probe for each cylinder.
Check your spark plugs for any signs of fuel and change them to eliminate that as a cause. I would also not recommend running your car with a damaged cat because the problem will get much worst.
A good cat used for normal driving should not fail as easily and I would question the quality of AP after another failure. I have a Magnaflow 3" cat for four years and I have never had any issues with even when my plugs had few misfires.

 

[Faded95]

Oldsid - Thanks for your reply. I don't know why but I hadn't even thought about the placement of my EGT probe, it's in my #4 exhaust runner (timing side is # 4 right?). I've got an appointment in the morning to put a new Vibrant cat in and I'll be running fuel system cleaner through tonight; the more and more I think about it, the more I think it's excess fuel. Might even replace the injectors...

I only have a narrowband O2 setup and it indicates more of a rich mixture - definitely have soot on the rear bumper too.

@cisco - full smog check here, car goes on rollers for a 2 speed test, I failed a few times last summer and that's why I replaced the cat in the first place.

 

[Warpathdsm98]

aftermarket cats really don't seem to last very long from my experience. I usually get about 2 years out of one on a daily driver. A misfire will kill your cat in a hurry aswell so make sure you figure out that situation before installing another cat.

 

[Oldsid]

Another possibility that sometimes goes undetected is a bad injector electrical connection. It may cause random misfires and in time may cause cat failure. Check if your injector connector is snug and not loose. Clean your injector connectors with an electrical connector cleaner to eliminate bad electrical connections.
If you are going to change your cat, use a reputable brand that will last or use a cat with a metallic core which will support the higher temperatures. I know Vibrant makes a round one, which if it fits, could be another solution.

 

[Faded95]

I'll check my injector connections, also going to check my timing, pull my plugs to inspect (new last summer).

I actually ordered the metallic core cat from Vibrant off Amazon but the one I got was a knock off so I am sending it back today. I thought about it and decided to order the Vibrant oval ceramic core from Extremepsi, so that's on its way; also picked up an OEM fuel filter while I was at it.

A friend of mine brought up that it could be bad 02 sensors - any thoughts? If so, how do I test them?

On another note, I also bought a couple of v-band assemblies to flange the cat in instead of welding it - save me some effort if I have to replace it again.

 

[Oldsid]

The front oxygen sensor is another possibility. Did you get any CEL? If the oxygen sensor is old, it may deteriorate to the point where it can cause either a rich fuel mixture.
I am not sure how to test an oxygen sensor on a 2G. On 1G, you can check the voltage at pin 4 on the ECU. The engine should be warmed up and the engine speed held at 2000 rpm. The voltage should fluctuate between 0 and 0.8 V. I assume that the procedure would be the same except that you need to test on the correct pin for a 2G.
You can also measure the voltage directly on the wire from the sensor by piercing through the wire jacket with probe. Use a digital voltmeter and make sure you measure on the signal wire that goes to the ECU (the white wire on a 1G).

 

[motomattx]

Your car is old enough that I cant see why its not exempt? number two, your car is a 1995 which does NOT have to meet obd2 specs anyway, it only has to meet obd1 specs as 1996 was the first year for obd2 mandate in America. Just because your car plugs into the obd2 scan tool does not mean that it has to meet obd2 emmisions specs, you might want to research that, maybe your state laws are wacky or something.