Any way to test if a Cat is plugged? - PeachParts Mercedes-Benz Forum

ps2cho · #1 10-23-2008, 05:37 PM

I was talking to a friend about my hissing sound at the back of the engine....and he says that I should check out the Cat.

Now -- I have had a long oil leak via bad stem seals before I bought the car and I've personally seen the cat glow purple one night.

With the hissing, poor power, bad mpg and the prior oil leakage....what could be the chances my cat is done for?

Is there any way to test this or is it just a replacement job?

79Mercy · #2 10-23-2008, 05:51 PM

mine has the hissing too, its the fuel pump.

If the cat was glowing then its probably plugged.

TheDon · #3 10-23-2008, 05:52 PM

if your cat was glowing its either toast or pretty close to some level of toast

ps2cho · #4 10-23-2008, 05:56 PM

Quote:

Originally Posted by 79Mercy

mine has the hissing too, its the fuel pump.

If the cat was glowing then its probably plugged.

Quote:

Originally Posted by TheDon

if your cat was glowing its either toast or pretty close to some level of toast

Found the pic

Think its toast?

79Mercy · #5 10-23-2008, 06:00 PM

well its so hot you could make some toast

If its purple then yes its toast. Do you live in a state where they check emissions?

ps2cho · #6 10-23-2008, 06:03 PM

Quote:

Originally Posted by 79Mercy

well its so hot you could make some toast

If its purple then yes its toast. Do you live in a state where they check emissions?

California. My car barely passed emission tests, but it did.

My friend also said the pressure from his daughters 4cyl Renault Clio's exhaust puts out more pressure out of the exhaust than mine. This doesn't sound right does it? My engine is alot larger and more powerful.

CWW · #7 10-23-2008, 06:03 PM

It's easy to check for a plugged cat.

Just remove the pre-cat o2 sensor on the side of the cat you want to test, and then hook up a pressure gauge in the threaded hole. There should be very little backpressure with a properly operating cat, so if you see a decent amount of pressure you know it's time to change the cat.

iwrock · #8 10-23-2008, 08:28 PM

Thats your precat, the cats are further back....

Its glowing from excess heat....

Running lean in the back?

I tracked the blue wagon last summer, and at the end of the day, the brakes were toast, and the exhaust was bright red.

Oracle12345 · #9 10-23-2008, 08:37 PM

you can test if you have a clogged cat by testing your oxygen sensors. the one before the cat should show voltage change in cycles and the one after shouldnt. If it doesnt then you have a bad cat.

ps2cho · #10 10-23-2008, 08:42 PM

I just got back from the shop and he banged the Cat and it sounded like a Christmas tree

Totally broken. Both precats and the main cat.

He quoted me $850 for everything, but I'm sure I can get it cheaper elsewhere.

What do you guys think about putting Magnaflow Cat's on there. They should be a ton better than the OEM based on technological advanced and improved airflow right?

yal · #11 10-24-2008, 01:23 PM

Actually $850 is really not a bad price for everything if you consider dealer prices

gmercoleza · #12 10-24-2008, 04:04 PM

The question is, why did the cats heat up and melt? They could've just broken down due to age, but you should make certain to correct any other issues (eg. rich mixture, improper timing, etc.) before installing the new cats on there, otherwise you'll just burn those up too in short order.

retroguybilly · #13 10-24-2008, 05:46 PM

Yeah, I was gonna say that, in my (admittedly limited) experience, the failure mode for cats seems to be getting blown out, not getting plugged.

I paid only $100 for a new MagnaFlow cat converter, after which my 420SEL passed California smog with flying colors. As a matter of fact, the emission numbers were just about zero!

But I had to cut a hole in the MagnaFlow cat and weld the bunghole for the O2 sensor from my old cat into it. Otherwise the MagnaFlow cat was just about identical to the factory-issue item.

All right, all right, let's not hear any jokes about Bungholio, OK? Every time I say the word "bunghole" around my shop, I never seem to hear the end of it!