Bad Cat Converter And Engine Knocking

[Guest Luis Eduardo]

My 94 850NA has been experiencing light engine knocking at up to 2000rpm for some time. I know my cat converter is bad as some noise of loose or cracked interior is clearly audible. Is it possible that knocking is caused by the bad cat as perhaps it is partially obstructed, thus affecting not only exhaust itself but the readings of the two oxygen sensors? Yes I get codes 435 and 436 every 150 miles or so. Thanks!

[Guest Guest_whilst_*]

No, the catalytic converter won't cause it.

Knock sensors detect vibration(s). Have you tried higher octane gas?

It's possible you have a loose accessory.

You can re-torque sensor or replace if that doesn't work.

[wattsat]

Not certain if it will cause knocking, but a blocked Cat is a very bad thing.

If you live in a state that checks exhaust, buy a replacement cat. They are not that expensive. Total costs + Labor should be under $300.00.

If they don't check or test exhaust, put in a striaght pipe, or put in a straight through muffler in the same location as the cat.

On my Porsche, the engine was running very rich. Eventually the Cat became fuel soaked, overheated, melted, caused the engine to die and then shot molten fragments out the back of the exhaust. I watched these glowing balls bounce down the highway as I coasted off and into a parking lot to wait for a tow.

Fix the exhaust first and then see if your engine knock goes away.

[DashingDaryl]

If I understand the EGR thing properly, your car shoots Carbon Dioxide ito the Throttle body to cool off the detonation chamber (Or something like that) If your EGR isn't working properly, then you get a knocking noise.

Since the EGR and the Cat are all tied to the emissions system, I'd think the two are related.

Your first step should be to read Rich's write up on the EGR system.

Rich's EGR Cleaning Write Up

the next would be to check for codes and see what they say.

I'd fix the cat first, and see what symptoms that fixes..

[icelandic]

Thanks to all that replied. I have already ordered a new Cat at FCP Groton. As I had an episode of floodind the engine with gas after I inadvertently let water accumulate on the spark plug housings after washing the engine ( It would not start, and I unfortunately only figured it out when idecided to check the plugs for spark), I kind of expected to have a cat problem. Now I have it. The engine knocking has been there for some time, and it disapears when I use high octane.

I will replace the cat and see if knocking goes away. But will consider the EGR clean up. I have never done it, but I do know that the vaccum lines are OK and that the apperture close to the throtle body is clear.

Thanks again.