Do I have a restricted Catalytic Converter?

[BlazerLT]

Looks like my Cat Convertor is on the edge of being plugged.

This has been ongoing for quite a while with low performance once the engine has been run for 100+kms and the engine is really up to temperature.

Also the idle is really crappy after long trips only or after the engine has been really driven for a while.

It is completely tuned up but it is still pinging under light load and just boggy unless you floor it.

The exhaust coming out of the tailpipe is very hot and you can only hold your hand near the tailpipe for about 1-2 secs.

Had a cat back pressure tested but the dumb morons at the dealership tested the back pressure after the truck has been sitting for 30+ minutes.

No wonder they didn't detect a problem. The cat wasn't warmed up yet.

 

[2003TRD]

I had a 2001 MR2 spyder and those cars have big cat destruction issues, well My car lost almost all its power, I was close to home, so I cautiously drove it home and took the cat off and took it for a spin to see if it improved, well it did, come to find out the fuel pump/pressure regulator were going bad. So one way to check is to just unbolt that sucker and go for a spint to see if it resolves the problem.

Another thing that I read is that with the MRs (and assuming other cars too) cats going bad, they gradually loose power until it will not rev into the higher rpm range. So the car still wouldnt have power when cold. it just slowly collapsed until there was a ton of engine exhaust back pressure and destroyed the shortblocks

 

[BlazerLT]

I had a internally leaking fuel pressure regulator on this GM 1995 CPI Injection 4.3L engine and I had to swap out the injector in June of this year.

Repair done:

New CPI Injector and internal Fuel Line Kit
New AC Delco Rapidfire Plugs (gapped properly)
Cap & Rotor 2 years old (10,000miles)
Cold Air Intake
Ravin Z55 Performance Muffler
Water Decarbonized

The thing is, I think the engine has been slowly cleaning itself out and clogging the cat. As I said before, it will have lots of pep when cold or warming up but once it is warm, the performance is not there anymore which leads me to believe I have a cat that is heating up and restricting.

It is also pinging when warmed up, not major, but it is there. Also noted, the exhaust is a lot louder when I start up the truck and the exhaust flow out the tailpipe is also more apparent. I have an after market exhaust so it is supposed to be louder.

When the engine is warmed up, the tone is not as loud. Also, a light rattle can also be detected when the engine is hot. More like a faint metallic shudder than a rattle. I went out to the truck when it was cold and slapped the cat moderately hard with the palm of my hand to see if it rattled and it didn't.

Get this though, I started up the truck and moved it to the parking space next to mine in 20 seconds and when I went under, the pipe betwwen the y-pipe and the cat was warm but the pipe between the cat and the muffler was cool.

You think I got a restricted CAT guys?

 

[tpi]

quote:

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Originally posted by BlazerLT:
Looks like my Cat Convertor is on the edge of being plugged.


Had a cat back pressure tested but the dumb morons at the dealership tested the back pressure after the truck has been sitting for 30+ minutes.

No wonder they didn't detect a problem. The cat wasn't warmed up yet.

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I would think the cat would be plugged hot or cold. If the converter passed a back pressure test after sitting a half hour, I would think it is OK. Are you hearing rattles from the converter?

 

[BlazerLT]

Ok, just got back from Midas.

They were really good to me and put it on the hoist and brought out the infrared heat sensor gun to test exhaust temperatures.

Ok, when the engine was warmed up and at idle, the inlet pipe 1/2 inch before the cat read 240c and the cat rear flange was 440c.

That is 200c in one foot. The one repair guy brought over the old shop guru and he explained that a good running cat should be hotter on the exhaust of the cat than the inlet for it.

to test this they revved the engine up and down for about 2 minutes and they checked the temperatures again.

Both inlet and outlet were about 350C which means that the cat is working properly.

Makes sense though and I am glad I didn't replace it.

I guess, if there is a blockage, before the cat is where the temperature would be higher as they explained and that does make perfect sense also.

Your thoughts guys?

 

[Gary Allan]

Easy check for this. Compare cold and warm vacuum readings at idle and the rpm range that the "wet cement" occurs. The vacuum should vary little with NO LOAD at various rpms. That is, whatever you get for a 2500 rpm no load reading ...you should get cold and warm (or some basic minor variance) ...if you see a BIG spread when warm ...you have a "thermally reactive" cat blockage. This is not unheard of. Typically they just break something loose (the honeycomb stuff) and physically block..sometimes however ..they do as you describe.

 

[V6 Diesel]

When the cat on my 5.7 chevy plugged I hardly made it home, could barely hit 20mph. Tried it cold the next day and same result.
Kind of funny my fuel mileage never changed any while it plugged up. Was getting just over 20mpg, kind of expected a drop in mileage.

 

[New]

crappy idle when hot might come from the EGR.
check the the coil packs too (even though a coil pack intermitent failure is sooo hard to "catch")

 

[ediamiam]

Defective EGR will cause pinging under load.

 

[ChrisW]

A heat soaked MAF will cause sluggish engine performance after a while.

 

[BlazerLT]

Just as an update, the cat started to rattle when revving just above idle and was getting rather embarrassing.

Went to Midas and had a new Magnaflow high flow cat installed and the rattle went away.

The front bisket was only slightly loose when the cat was hot and causing the rattle.

When they gave me the old cat I looked through it and it wasn't restricted bad at all, just slightly loose. Don't get me wrong, it wasn't nearly as unrestricted as the new one.

But man, does the exhaust have a growl to it now.

I mean seriously, what a sound difference, I LOVE IT!

The old cat was twice as wide as the new one and was acting sort of like a resonator.

 

[Rob Taggs]

I would say I'am with you on assuming the converter is clogged. I had a 1986 Firebird that would blow intake gaskets about every 10,000 miles or so. Well, I kept taking it to the dealership where I bought it to have the gaskets replaced. This happened 5 times with the same shop and at $600.00 everytime. The sixth time rolled around but, to my amazement the dealership had changed hands - New Owners! This time with new mechanics who told me that they felt it had to be the converter, which weighed a ton. To make it short, I never had anymore blown intake gaskets from that point on.

 

[Yuk]

quote:

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I mean seriously, what a sound difference, I LOVE IT!

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Cool! Do you notice a performance improvement?

 

[JTK]

BlazerLT- You have a "cold air intake" kit installed? are you sure you dont have a dirty/fouled MAF sensor? This can cause the issues you have once the vehicle is warmed. Cone filters can let in more dirt, or oiled filters can coat the MAF sensor with oil, causing the concerns you describe.
G/luck
Joel