is there an easiest test to determine if cat getting plugged?

Reply

  #1  
Old 07-12-09, 10:53 AM
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: May 2007
Location: Wisconsin
Posts: 8,629
is there an easiest test to determine if cat getting plugged?

Got idea for thread from truck hemi thread.

It seems to me that if a cat starts to plug, due to other problems people may have been having with especially high-mileage vehicles, that perhaps the cat may be slowly plugging up and robbing the car of it's maximum efficiency. Obviously, unlike with certain reasonably priced vehicle parts, you just don't want to go and throw a new one on and see. For in many cases the price of the cat may be more than what the old car is even worth.

Any good cheap easy way to really determine that? It may be more obvious if say an old vehicle has no more top end, or something. But what if say the vehicle still runs pretty good, but gas mileage has fallen off say 3 mpg. Yes, I know about o2sensors. But what if you also want to check the cat? Can anything be made to rattle in a bad one?, or does it just get gooked shut after a while, or what?
 
Sponsored Links
  #2  
Old 07-12-09, 11:09 AM
Unclediezel's Avatar
Member
Join Date: Dec 2006
Location: Northeastern PA.
Posts: 2,230
Yes and no.....

A cat that rattles inside is Junk......
If it is plugged up, and causing performance problems, Remove the O2 sensor in front of it, and drive the vehicle....Removing the sensor allows a Hole for the trapped exhaust to escape, thus temporarily eliminating your driveability issue.

As far as Just checking a cat for "The hell of it"....Not really...

There are usually 2 O2 sensors for each cat, 1 before and 1 after...The PCM looks at the first for a reading, and looks at the second for the "Modified" reading that passing thru the cat has produced. Anything less than a 97% efficiency rating indicates a worn out, or Burned out cat.

Yes I know in theory that a "Post Cat " o2 sensor can cause erroneous ratios and trip a MIL..But in the real world, very few O2 sensors are responsible for Catalyst Efficiency DTC's.

There is a huge difference between a Clogged cat, and an Inefficient Cat. They are total opposites... A clogged cat will not allow exhaust to pass thru...An inefficient one will allow the gas thru it, but not produce the required reaction. Efficiency problems are usually caused by age or physical damage, while the clogged one is usually a poor running engine , which emits raw fuel into the exhaust system, and either Carbons up the cat, or Burns inside the cat and melts it.
 
  #3  
Old 07-12-09, 11:19 AM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
depending on what type of medium is used in a cat converter, it can have one of several problems.

In a solid medium, which is what most, if not all current models use, there is a honeycomb of precious metal infused onto a ceramic substructure. There are generally 2 things that happen with this type.

1. the ceramic honecomb breaks up. When the honeycomb turns sideways, it can block the exhaust flow. This type of damage can generally be determined by taking the end of your fist and hitting the converter (not when it is hot). If it rattles, this is most likely what happened.

The other thing that can happen is; it can be superheated by an overly rich fuel mix in the exhaust. It is supposed to heat up and burn off excess fuel but too much can make it get so hot, the shell will actually glow red. This often results in the breaking up of the substrate but it can get hot enough to actually melt the substrate, which will, of course, block the ex flow.

the other type of converter is what GM used. It was a shell filled with beads that contained whatever precious metals needed to cause the catalytic reaction. Is some cases, those beads fused and blocked the ex flow.

most cats do not get gunked up simply because what they do is get very hot so as to convert the exhaust gasses to a less objectionable mix of pollutants. If part of the converter would get gunked up, all of the ex flow would have to go through whatever area is left and it would most likely cause that area to superheat and resultingly, burn off the gunk.

this is one reason you never use leaded fuels in a car with a converter. The lead is not altered by the combustion and ends up plugging the converter.

I suppose that is about the only way I have heard of a converter being gunked up to the point of being plugged.

so, how to check?

tough call. broken substrate as noted above

plugged? the engine will lose top end due to the blockage. Some vehicles you can notice an exhaust leak only at higher RPM. Since most vehicles have a moving exhaust donut seal, it can allow the excess pressure to escape. This, sometimes, can actually be heard. This also burns out the ex donut sometimes, eventually, as well.

a good portion of the time it is simple; an educated guess
 
  #4  
Old 07-12-09, 12:10 PM
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: May 2007
Location: Wisconsin
Posts: 8,629
Will pointing an infrared thermometer at one give a clue? Or are the temps higher than say 650 degrees (beyond the range of an infrared gun).

How hot should a properly working cat get, about? Or do they vary widely with a car that say has a huge V-8, and another is a little 3 or 4 cylinder, let's say.
 
  #5  
Old 07-12-09, 12:49 PM
Unclediezel's Avatar
Member
Join Date: Dec 2006
Location: Northeastern PA.
Posts: 2,230
yes, you can judge by temps, but it isnt foolproof......
 
  #6  
Old 07-13-09, 08:03 AM
Member
Join Date: Jun 2009
Location: California
Posts: 214
Cats

If you attach a manifold vacum gague to a vacum port on the intake manifold/ easily aquired at Sears. Run the engine at idle and monitor the value, should be around 15 inches or so. Then raise the engine speed to lets say 2200 RPM, the reading should be the same or a bit higher. If there is a restricted exhaust the value will drop quite remarkably. I have found many cats with that test.
Bill
 
  #7  
Old 07-13-09, 03:54 PM
Unclediezel's Avatar
Member
Join Date: Dec 2006
Location: Northeastern PA.
Posts: 2,230
Tijoe.....

Only one problem...While yes your test is valid, it will only show a "Restricted Exhaust...." ..period.... With most cars these days having as many as six converters, which one is the Culpriit????

There is really no way to isolate a restriction by taking readings at the intake manifold.. since it shares a common outlet with ALL exhaust components..
 
  #8  
Old 07-13-09, 03:58 PM
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: May 2007
Location: Wisconsin
Posts: 8,629
Originally Posted by Tijoe View Post
. If there is a restricted exhaust the value will drop quite remarkably. I have found many cats with that test.
Bill
That makes sense! You'd have..... open throttle, yet lesser rpm's = less vacuum.
 
  #9  
Old 07-14-09, 05:17 PM
Member
Join Date: Jun 2009
Location: California
Posts: 214
Cats

For what it's worth Uncle adding additional factors after a question is asked doesn't invalidate an answer. If an actual shop was doing the repairs this question wouldn't be asked on this forum. An actual shop would have both a hoist and a digital pyrometer and even an electronic stethyscope to allow more in depth investigation. I was actually a technical instructor for a large local franchise in Los Angeles for the last couple of years of a 40 year technical career. Evaluation of catalytic function is more demanding than relying on one method and the expense of cat replacement would suggest the process would be better accomplished by an working professional in a shop.
Bill
 
  #10  
Old 07-14-09, 08:03 PM
Unclediezel's Avatar
Member
Join Date: Dec 2006
Location: Northeastern PA.
Posts: 2,230
Tijoe,

That wasnt meant to Invalidate anyones answer, I agree with you completely, as far as testing in a shop environment. Just simply put, these guys dont have access to the "Shop Environment"....and since most of these questions involve the "Overcooked Import" variety, I just didnt feel that the "Generic" procedures would suffice. The first thing that comes to mind is the "Mani-Verter" style exhaust manifold. Well within the scope of a DIY'er to replace, but tragic to find out the muffler is Plugged solid after spending 1100 dollars to replace the converter....

Like I said, it wasnt a Bash, or an attempt to Invalidate your opinion, and if you took it as such I apologize.
 
  #11  
Old 07-15-09, 06:45 AM
Member
Join Date: Jun 2009
Location: California
Posts: 214
The forum

I play answer man on a couple of other boards and at times become frustrated at the lengths some will go to trying to avoid diagnostic charges. Accurate diagnosis and of course repair isn't an easy task, being a effective technician can be vary challenging. I attempt at times to share what 40 years taught me but it isn't always an easy thing to do as for many this is a way to repair a needed item inexpensively because the money is otherwise spoken for. And I at times miss the challenges provided by taking the next car up. No problems here.
Bill
 
  #12  
Old 07-15-09, 12:44 PM
Member
Join Date: Jul 2009
Location: California
Posts: 1
On newer cars if the the cat is plugged then it will trip a CEL. Then all you have to do is run the codes with a scanner and it will tell you what the problem is.
 
  #13  
Old 07-15-09, 02:58 PM
Unclediezel's Avatar
Member
Join Date: Dec 2006
Location: Northeastern PA.
Posts: 2,230
Originally Posted by Tijoe View Post
I play answer man on a couple of other boards and at times become frustrated at the lengths some will go to trying to avoid diagnostic charges. Accurate diagnosis and of course repair isn't an easy task, being a effective technician can be vary challenging. I attempt at times to share what 40 years taught me but it isn't always an easy thing to do as for many this is a way to repair a needed item inexpensively because the money is otherwise spoken for. And I at times miss the challenges provided by taking the next car up. No problems here.
Bill
Im glad there is not a problem between us, and More-so pleased that someone else shares my frustration over the cost of Diagnostic charges, and Competent repairs. Although it isnt quite as long as 40, 26 years of watching most of the general public staring at their wallet before they even come in the door, or whipping out the WARRANTY card for a slashed tire or Broken window , has sort of left me NUMB to why I started in the business to begin with.

An older gentleman told me, when I started in the Biz....."You will NEVER meet a vehicle that cares if their owners wallet is empty"...
 
  #14  
Old 07-15-09, 03:08 PM
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: May 2007
Location: Wisconsin
Posts: 8,629
Originally Posted by Tijoe View Post
I play answer man on a couple of other boards and at times become frustrated at the lengths some will go to trying to avoid diagnostic charges.
Thanks Bill for your help so far. I have only 1 cat and 1 muffler so at least with your vacuum test, at least I'd(or anyone else interested) maybe know that something is more plugged than it should be, in the exhaust. That is a pretty good start, I'd say, even if then one has to then determine if it is the cat or the muffler.

Regarding the portion of your quote which I posted above: This is why we have this forum. So we can DIY., if at all possible, if we can learn hints, tricks and methods as to how.
 
  #15  
Old 07-15-09, 03:43 PM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 20,800
Ok I just have to..I've wanted to since I saw the title of the post....

"Is there an easiest test to determine if cat getting plugged?"

answer...If you don't see anything in the litter box or on the carpet...your cat is getting plugged!

I said I was sorry...lol
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'