How do I know if I need a new catalytic converter?

[coreydmc]

I have failed inspection due to emissions. I also noticed the wire pulled out of the oxygen sensor. Would that have anything to do with it? Also if I need a new cat is it as simple as replacing it myself or does my fuel injection need to be tuned to the new cat?

[David T]

If your O2 sensor is not connected the fuel system is not functioning as it should so it is no surprise you did not pass emissions testing. I would not immediately suspect the catalytic converter. First step would be to hook up the O2 sensor and see if you can get the Lambda system running as it should. You may have to replace the O2 sensor, fix vacuum leaks and adjust the mixture screw. Once you get the Lambda system going you don't even need a cat to work in most States. A Delorean runs so clean it will pass without a working cat (if everything is working as it should). A plugged cat will be noticeable by restricting the exhaust. At high RPM's the motor will start to "pull back" and lose power.
David Teitelbaum

[DMCVegas]

What do your emissions readings look like?

[stevedmc]

Based on another person's logic on this forum, your 30 year old catalytic converter should be replaced and then checked for leaks. Its old so you should replace it whether or not its working fine.


Edit: On a serious note, does your cat glow red and do you see any burnt paint on the frame below the cat? Is your heat shield still below the cat?

[coreydmc]

i will get the reading to you guys later. they are outside in the car. also if i do go the route to get a new cat and 02 sensor i was thinking about special t's. What do you think? His price seems very reasonable

[sean]

Based on another person's logic on this forum, your 30 year old catalytic converter should be replaced and then checked for leaks. Its old so you should replace it whether or not its working fine.


Based on another person's logic he should install an alternative fuel deliver system.

[stevedmc]

Based on another person's logic he should install an alternative fuel deliver system.

You forgot to mention Spec .01 exhaust.

On a serious note, Hervey's looks nice. If I remember correctly it even has a built in heat shield.

One other thing to ask is hows your gas mileage? Did it suddenly drop? A sudden drop in gas mileage could mean your car is running rich. Too rich of a mixture could very well mess up your cat.

[rundmc]

Hervey's looks nice on the wesbite, but the welds upon arrival are sloppy - see photo of mine recently installed.

http://4.bp.blogspot.com/-9DKebUxKga8/T2fr9plSfWI/AAAAAAAAAlM/-78V1f7gIlc/s1600/IMG_1812.JPG

[stevedmc]

Hervey's looks nice on the wesbite, but the welds upon arrival are sloppy - see photo of mine recently installed.

http://4.bp.blogspot.com/-9DKebUxKga8/T2fr9plSfWI/AAAAAAAAAlM/-78V1f7gIlc/s1600/IMG_1812.JPG

Do the welds leak? It looks better than a 30 year old rusted cat to me.

[rundmc]

Do the welds leak? It looks better than a 30 year old rusted cat to me.

When I get my car started I will let you know. :(

[DMCMW Dave]

Do the welds leak? It looks better than a 30 year old rusted cat to me.

Here's what a 30-year-old NOS/OEM cat looks like. $225 Plenty available.

9495

[jawn101]

Here's what a 30-year-old NOS/OEM cat looks like. $225 Plenty available.

9495

Ah, so that's what they used to look like :) Too bad there's no heat shields anymore. No one seems too rushed to make replacements - is the shield even necessary?

[DMCMW Dave]

Ah, so that's what they used to look like :) Too bad there's no heat shields anymore. No one seems too rushed to make replacements - is the shield even necessary?

I see lots of cars without it. As long as you don't screw up the fuel system and get the cat red-hot it doesn't seem to hurt much. It's a legal requirement for the car maker. On most cars the cat is much closer to the ground and it's actually there to keep from setting dry grass on fire.

[jawn101]

I see lots of cars without it. As long as you don't screw up the fuel system and get the cat red-hot it doesn't seem to hurt much. It's a legal requirement for the car maker. On most cars the cat is much closer to the ground and it's actually there to keep from setting dry grass on fire.

Ahh, that makes sense. I have a tiny patch of the original one still left. The grass is safe.

[stevedmc]

When I get my car started I will let you know. :(

Dang dude. Are you replacing everything at the same time?

[jawn101]

Dang dude. Are you replacing everything at the same time?

Was just thinking the same thing. Lesson one with the D - tackle one system at a time. Do too much and you'll have so much more difficulty troubleshooting.

[rundmc]

Dang dude. Are you replacing everything at the same time?

The original winter plan had been to do a coolant flush and swap the converter to a new one and put in new motor mounts -- that was to be it.

The coolant flush revealed leaks, which revealed a coolant leak in the VOD, which led to the intake removal and water pump replacement (leaking thru gasket). "While in there" I decided to do cap, rotor, wires and plugs. Not planned for, but I thought I was being a responsible owner - more responsible than the PO anyway. I don't regret my decision despite my difficulties. This car clearly had a lot of neglected systems that need tending to.

[coreydmc]

once i install the new cat and o2 sensor how do I adjust fuel mixture? how can i tell if it is rich or lean?

[jawn101]

That's a long question. The short answer is to verify your idle is set properly at 775 +/- 50, jumper the RPM relay so the frequency valve activates, then use a dwell meter to probe the FV (orange wire on the diag plug and ground to engine). You want to see it at 45 degrees on the 4 cylinder scale (yes, even though this is a 6 cyl engine). Press the WOT microswitch and it should jump to 55. If it does, congrats - your lambda system is working. If it doesn't, you have to figure out why and fix it.

Reinstall the RPM relay. Start the engine and verify the dwell still reads 45 degrees and that the FV is buzzing.

Get the engine warmed up to operating temp (fans cycling is a good sign). The dwell meter should be swinging left and right. You want to see the low point of the swing at 30 and high point at 50, centered around 40 (again on the 4 cylinder scale).

If it's not centered properly, turn the mixture screw in hair's widths - this is a very very sensitive adjustment. Turning counterclockwise will lean the mixture, moving the dwell higher if it's too low. Clockwise will richen the mixture, moving the dwell lower if it's too high.

Once you're reading 30-50 centered on 40, you're done. Be sure to put the plug back in the adjustment hole after each adjustment to make sure your reading isn't skewed based on a vacuum leak.

If you're seeing any behavior other than this, then you've either hooked the dwell meter up wrong or something else is wrong in your engine or electronics and you need to address that before proceeding further.

Don't do any of this until you're sure that the fuel and vacuum systems are entirely leak free and that the idle is smooth and set correctly. Also don't attempt it unless you're absolutely sure you have the right tools and knowledge for the job. This is a sensitive adjustment and can take a lot of fiddling to get right. If your tamperproof plug hasn't been taken out of the mixture control unit, *seek a vendor's guidance*. I can't stress that enough. It's entirely too simple to make one slip of the hand and f*#k up your mixture unit.

Also this doesn't guarantee emissions, just that the fuel mixture coming into the engine is right. You may still fail smog checks if there are other problems, such as a bad cat. Exhaust gas analysis is the only way to know what's coming *out*, this just helps make sure the right things are going *in*

Also, credit where it's due! Dave S above is the one who helped me learn all this. Without him I never would have gotten it right.

[mluder]

I wasn't passing emmisions either.

I removed the 30 year old cat and found a pile of rubble inside.

Installed John Hervey's and a new O2 and passed with flying colors.

Not saying that's all you need but a place to start.

[coreydmc]

WOW! thats a ton of info there. I will tackle this on a weekend. Im sure I will have questions so please stand by!!!! lol! If I take these readings now with old cat they shouldnt change when new cat is installed right?

[deloumis]

WOW! thats a ton of info there. I will tackle this on a weekend. Im sure I will have questions so please stand by!!!! lol! If I take these readings now with old cat they shouldnt change when new cat is installed right?

The O2 sensor comes before the cat so I wouldn't think so.

[coreydmc]

hopefully this will clear up the harsh exhaust smell. it is not a rotten egg smell but it is a strong smell. you cant even stand behind the car. if you do your clothes will stink all day long like fumes.