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Symptoms of a clogged catalytic converter.....


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18 replies to this topic

#1 travis

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Posted 11 March 2005 - 12:52 AM

My car is running horrible right now. It seems to have very little power, idles rough down low, and is running hot all of a sudden.

What are the symptoms of a plugged converter?

#2 Snowman

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Posted 11 March 2005 - 01:37 AM

A plugged cat will not allow the engine to rev much, even in neutral. Aside from that, I'm not sure of the symptoms.

#3 mons72

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Posted 11 March 2005 - 02:05 AM

if you shake the cat and hear everyting in it moves, then the cat is gone. even if a cat is broken, the engine can revs up normaly. i had a car were the cat was broken, and i didn't have trouble with the engine to rev up. try to shake the cat and hear if there is some parts in the cat that's moving arround in there.

#4 bigjim5551212

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Posted 11 March 2005 - 02:17 AM

a broken cat will usually flow exhaust. It wont pass emissions mostly. and it rattles. with a plugged cat you will find that you will not feel any exhaust pulses at the tail pipe. there will be just hot air coming out slow

#5 ausubaru92

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Posted 11 March 2005 - 05:29 AM

When mine blocked, it would squeel/whistle if i reved it up high, not to mention the extreme lack of power, and no exhaust pulses from the tailpipe

#6 stephenw22

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Posted 11 March 2005 - 03:34 PM

My turbo wagon had a pretty clogged cat before I had it (COUGH!)removed(COUGH!).

The main symptom was that I had no power above 3500 RPM. I couldn't even get it to rev much past 4000 RPM if I tried.

After I had the cat removed, I was absolutely amazed over the performance improvement. All of a sudden my engine was ALIVE! I still remember how much I smiled the first time I floored it in 1st gear and took it to the redline.

#7 grossgary

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Posted 11 June 2007 - 10:08 AM

yes, i know this is old...but rather than start a new thread:

my legacy barely idles, cuts out unless i give it gas and won't hold RPM if i hold the gas pedal in one position, it will die unless i'm varying the gas pedal position. barely moveable if i try to drive it. i had the exhaust off and was banging it, jarring it, slamming it to get a tool out that fell in it....nipper suggests i might have a fouled up converter. car/engine ran fine before the engine swap and this exhaust "work".

if this is the cause of running this bad will the lack of pulses out the tail pipe be obvious? don't think i can get it idling long enough to check though.

can i unbolt it from the headers and run it without the exhaust to test? i know the older generation soobs run fine like that..very, very, annoyingly loud, but you can at least drive them a mile without any exhaust just to check. same with the EJ stuff?

i know all that abuse i gave it could have knocked the converter loose, but would that really cause it to "clog" like this right away?

#8 Nug

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Posted 11 June 2007 - 11:16 AM

Here's how to test for a clogged converter (will not work on turbo cars unless boost is somehow removed). Connect a vacuum gauge to manifold vacuum port. Start engine. Vacuum should be in normal range, 17-22 (approx) inches. Rev engine to 2000 rpm. If converter is clogged, vacuum will drop several numbers and not recover. If converter is ok, when you hit the throttle vacuum will drop momentarily, but the return to the normal range.

#9 daeron

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Posted 11 June 2007 - 02:52 PM

the last time I discovered a clogged catalytic converter, the thing that made me positive was the fact that the exhaust system BEHIND the cat was cool to the touch VERY shortly after cutting off the engine, while the cat itself and the pipes in front of it were still WAY too hot to touch. something like, 30-45 minutes and the back half was cool.. but not the front. you dont have one of those IR laser thermometers, or a contact thermocouple, do you??

HTH

#10 Skip

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Posted 11 June 2007 - 03:12 PM

a vacuum gauge can be very helpful here.

The back pressure kills the intake manifold vacuum.

The result -> less air intake, less bang, less power.

#11 grossgary

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Posted 11 June 2007 - 03:44 PM

thanks guys, i appreciate it.
i dont have any temperature gauges, but i got two hands and 10 or so fingers. anyway and i don't have a vacuum gauge but probably should. if the temp to the touch and feeling out the exhaust pipe are indeterminate i'll probably get a vaccuum gauge. where do i hook it up???

#12 DaveT

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Posted 11 June 2007 - 10:15 PM

I have tested exhausts with a vacuume cleaner. Unbolt the Y pipe at the heads - enough to get an inch gap. Connect the vac to the tail pipe. There shouldn't be a big difference in air flow (speed of the vac's motor) with or without the exhaust. This is easier to determine if you have a spare / known good system to compare with, but if yours is really plugged as bad as it sounds, it should be quite noticeable.

I had a cat burn out, and piece of the core got stuck (sideways to the tiny holes) in the outlet of the cat housing. The engine ran ok at idle, light load, low RPM, but was flat / no power when I put the pedal down, pinging, and ratty.

#13 daeron

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Posted 11 June 2007 - 11:31 PM

I have tested exhausts with a vacuume cleaner. Unbolt the Y pipe at the heads - enough to get an inch gap. Connect the vac to the tail pipe. There shouldn't be a big difference in air flow (speed of the vac's motor) with or without the exhaust. This is easier to determine if you have a spare / known good system to compare with, but if yours is really plugged as bad as it sounds, it should be quite noticeable.

I had a cat burn out, and piece of the core got stuck (sideways to the tiny holes) in the outlet of the cat housing. The engine ran ok at idle, light load, low RPM, but was flat / no power when I put the pedal down, pinging, and ratty.


GREAT Idea!!!!!!

#14 Silentpal

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Posted 11 July 2007 - 04:21 AM

if the engine is out of tune up; excess fuel entering exhaust; oil or anti-freeze entering exhaust; bad spark plugs or spark plug wires; bad 02 sensor.. are some of the possible causes why subaru catalytic converter fails.. so better check on those things.. :)

#15 privateer56

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Posted 11 July 2007 - 06:56 AM

I was just looking at the link for the Subaru cats and had a thought. Has anyone tried to run a dual exhaust system with a second cat and all? I don't even know if there is enough room but if you offset the cats so they are not so wide (are there any aftermarket cats that are narrower?) while still keeping them the right distance from the engine to keep the right heat range and band clamp the two pipes together that may work. I have to believe that by halving the back pressure you would get some kind of an increase in power especially if you use a free flow cone filter system. Any thoughts?

#16 landovonderberg

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Posted 03 October 2008 - 12:53 PM

Hey yall. I've been searching usmb all day as my dad and I try to figure this out. I'm having severe backfiring issues. (87 GL sedan) My muffler's got a hole blown out and from the looks of things my y-pipe cat is rusted to ************. If I bypass the cat and make sure all the leaks in my exhaust system are plugged, will it still backfire? I'm pretty sure my carb is tuned decent. I'm idling at about 900-1100 rpm. I don't have to pass emissions since I live in the BC interior. I'm about to move to Ucluelet, near Tofino on Vancouver Island and I need to get this backfiring issue fixed before leaving(2 days). I just need to know if, by gutting my cat and piecing in a pipe, there will be a lack of backpressure which would result in more gunshot backfiring.
Just a little more info on the BF, it tends to bf hard when I let up on the gas when shifting gears, 3000 and higher rpms really scare the ************ outta people.

edit: btw I have a welder and a dogged determination to not spend money since I won't be able to afford food....if I can't fix my muffler by the time I head out then I'll just wait until i can afford a new one.
Help me turn my rusted out hunk into a surfmobile!

Edited by landovonderberg, 03 October 2008 - 12:56 PM.


#17 TeamCF

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Posted 03 October 2008 - 01:37 PM

I was just looking at the link for the Subaru cats and had a thought. Has anyone tried to run a dual exhaust system with a second cat and all? I don't even know if there is enough room but if you offset the cats so they are not so wide (are there any aftermarket cats that are narrower?) while still keeping them the right distance from the engine to keep the right heat range and band clamp the two pipes together that may work. I have to believe that by halving the back pressure you would get some kind of an increase in power especially if you use a free flow cone filter system. Any thoughts?


I had a better link but lost it in another computer I think.
But metal core Cats are smaller.
http://www.verocious...lytic-Converter

I was going to go for one last year.
Only prob is they tend to take more heat to activate.

I just removed my new cat, won't need it again for another year or so (When I'll throw another one on, neglect to remove it after passing DEQ, and smash it on a rock as well...rinse and repeat every set of tags). Some big rocks busted it all up. The broken chunks made my engine not idle. I could rev it up but it felt sluggish. Kind of a bummer. Got less that a year out of that one.

Man next year I'm gonna need most the exhaust replaced. cutting out and welding in too much I'm running out of room to work under there. :-\

#18 DaveT

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Posted 03 October 2008 - 09:58 PM

The vacuum cleaner test tests the flow capacity of the exhaust system isolated from the engine.

The vacuum pressure drop is very low. It would be measured in inches of water, or possibly fractions of an inch of water. A manifold vacuum gauge measures in inches of mercury.

You also need to move a huge volume of air through the exhaust system to simulate what the engine pushes through it.

If the engine only pumped air through (like when cranking)---

1800CC = .06 cubic feet.

4 cylinders takes 2 revolutions for each to fire once.

1000 RPM / 2 = 500 engine displacement volumes per minute.

500 x .06 = 30 CFM

So 2000 RPM would be 60 CFM
4000 RPM would be 120 CFM

The CFM exiting a running engine would be higher, I think, because the expanding gasses from combustion are not released from the cylinders at atmospheric pressure. From looking around a bit, something like 3-4 times higher. It varies with all kinds of things, especially how open the throttle is.

#19 XT6 Magic

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Posted 03 October 2008 - 10:47 PM

You can also poke a test hole in the pipe before the cat and measure the exhaust back pressure. I believe it should be no more than 2-3 psi normally and just weld the hole back up if you can't use an O2 sensor hole




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