Clogged Catalytic Converters? How can you tell?

[stkjock]

Gents,

I've notice in the last month or so that the exhaust on the car sounds different. I'm wondering if my cats are clogged. Car has 15,000 miles on it, 12,000 with the blower, driven not a show car.

So at idle every few seconds it sounds like a deep bass drum "thud" and when I let off the gas the "burbble and gurgle" that one usually hears seems louder.

The motor seems to run fine otherwise, pulls strong and feels ok.


Any insights for a non-experienced wrencher are appreciated.

 

[Embalmer]

I just replaced the converters on my 2003 Windstar. It was noticeably down on power and then it wouldn't rev at all nor drive over 30 MPH. Then it blew off a tube connected to the DPFE sensor, which told me there was excessive backpressure in the exhaust. I bought one of those laser thermometer guns and shot it at both converters. The front one was 100 degrees hotter than the rear when the car was warmed up. Temperature would be a good indicator if one of them was cooked. Here are the converter assemblies, the next pic is what came out of the pipes when I shook them upside down.

 

[bullitt boy]

Just a thought ,when I was hearing the thump sound or heartbeat like sound in mine it was a clipped plug.

 

[stkjock]

Just a thought ,when I was hearing the thump sound or heartbeat like sound in mine it was a clipped plug.

how did the car pull when this happened? the car pulls hard to 6500+

 

[TonyN]

Easy way to tell is with a vacuum guage. Hook a vacuum guage up to engine vacuum (I prefer the vacuum hose going to the fuel rail sensor). Or if you already have a boost/vacuum guage it's even easier. Take note of how much vacuum it has at idle while at operating temp (18-22 usually). Raise RPMs up to 2500-3000 and take note of guage movement. It should go towards 0 upon engine acceleration and fall back down to the same number you had at idle once you hold the RPM's. If it has less vacuum than at idle then that is a strong indication of a clogged cat and/or exhaust.

Basically you should have the same amount of vacuum at idle and when holding the throttle at a steady RPM. If you have less vacuum at say 3000 RPM than at idle, there is more than likely a restiction. If you fail this test then it would be time to visually inspect the cats. Sometimes you will hear the cat's rattling around when the fall apart as well.

 

[fdjizm]

I made a thread similar to this yesterday, if it goes down in vacuum extremely I believe that's when you have a problem and you have some back pressure caused by something.

http://s197forum.com/forum/showthread.php?t=36689

 

[TonyN]

Your vacuum looks perfect in that video (no indication of any restrictions). If you slowly increase RPM vacuum won't even drop, like you did in the video. If you snap it, it should go to zero and fall back down to what it was at idle once you hold the RPM.

 

[bullitt boy]

Car pulled great no other indication except the thump sound and an random old school type backfire ,which is when i decided to check the plugs. Plug #5 had a missing electrode and a gap of about 1/4" .

 

[fdjizm]

Your vacuum looks perfect in that video (no indication of any restrictions). If you slowly increase RPM vacuum won't even drop, like you did in the video. If you snap it, it should go to zero and fall back down to what it was at idle once you hold the RPM.

thanks bro! The first vid I took I noticed it when I cracked the throttle it went down then leveled out, had to throw the SCT tune back in so I can hold it stable at any rpm and that is this second vid. glad it's OK

 

[1FastS197]

Car pulled great no other indication except the thump sound and an random old school type backfire ,which is when i decided to check the plugs. Plug #5 had a missing electrode and a gap of about 1/4" .

thats a nice size gap! lol...

 

[bullitt boy]

The gap was that large due to the missing electrode it was scary to look at knowing I had been running the car like that.