Clogged Cat Question

rgoldberg

Original poster
Member
Dec 13, 2011
35
04 EXT 4.2 w/ 194K

Pretty sure I have a clogged cat. Monday on the way to work it was bogging down and died. Couldnt make it up a hill, but never illuminated the SES light. I got her home and took my silverado to work. Monday when i got home I cleaned the TB, installed a new Air filter, and fixed an air hose nipple on the resonator. Started her up and hardly any exhaust pressure, and then the SES lit up and Reduced power light. I checked the Fuel pressure, and read 54psi.
Well after a few repeated attempts the engine finally revved about 2k, and kinda drove ok. The reduced power light turned off, but SES still on.

Well today while waiting on my buddy to come read the code I decided to drill a hole in front of the Cat. The SES light immediately went off. Makes me think it was definitely an O2 sensor code do to a clogged Cat.

My question is, Would the SES light really go off that soon if it was an O2 Sensor code? I know some codes take many miles and proper speed to be reset.

I'll be replacing or gutting the Cat this weekend.

Thanks!
 

gladesteen

Member
Aug 19, 2014
83
goldberg,

Take it to an exhaust shop and they can diagnose it for you. The upstream O2 sensor will come out and they can hook a gauge threaded into the hole to determine if your cat is clogged.
I just went through this after my T-stat was stuck open and i drove it for months before fixing. The extra fuel bcuz of the engine running cool caused my cat to clog also. I ordered a new Magnaflow (rockauto) and all is well again.........of course i changed the t-stat prior. The new magnaflow pipe w/cat was around $170 iirc.

Dont gut the cat, it will cause issues with PCM and you will get SES, bad mileage and more. Some do gut the cat and buy extenders for the O2 sensors, but to me seems like more work than necessary.

Hope it helps ya.

Mark
 

Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
Really need to scan it when the light is on to give us an idea about why the cel and reduced power lights come on.

If you literally drilled a hole in the converter then you'll be replacing it either way, might as well go ahead and buy a new one after you see what the cel is coming on for.
 

AWD V8

Member
Jan 12, 2015
463
The usual simple check is to unscrew the O2 sensor ahead of the CAT and drive it. It will be noisy, but with the sensor removed it will pick up power quite noticeably.
 

DocBrown

Member
Dec 8, 2011
501
If you do replace the CAT with an OEM style replacement it's a real pain on an EXT. It's been a while since I had a GMT 370 but IIRC it was about a 4 hour job to replace the cat with 2 people. You will most certainly have to heat up the bolts going to the exhaust manifold.
 

rgoldberg

Original poster
Member
Dec 13, 2011
35
i pulled the CAT today, took about 20 minutes. All the bolts (15mm on manifold end and 12mm on muffler end) and the down stream O2 sensor came out easy with my impact wrench and some extensions. I cut the pipe just south of the cat and pulled everything out with ease.

Then I cut the Cat free to inspect it. Just looking at the Cat I dont think it is clogged but tomorrow I will cut it in half and see what the insides look like.
I do think it is odd that the manifold end is solid black but the muffler end is solid white, wait that's what it is supposed to do... Also the exhaust pipe upstream of the cat was very clean but every thing down stream towards the muffler is coated with carbon
 

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FearlessAZ

Member
Jun 7, 2016
156
Phoenix, AZ
I am curious how this turns out. Mine is acting the same after doing all the same things. I have wanted to look into the cat situation for a couple months but can never find the time. I will have to try and remove that front O2 and see how it feels.
 

rgoldberg

Original poster
Member
Dec 13, 2011
35
so last week the exhaust pressure from the tail pipe felt like a kitten breathing on the back of your hand, barely noticeable. After installing the magnaflow direct fit cat, it feels like a dame tiger breathing down your neck...the difference in exhaust pressure at the tail pipe is amazing.

I drove around the neighborhood, and out on the road for a quick run up to 60mph, she ran fine. Today i'll run some errands and make sure no codes are flagged.

The install wasn't horrible. I used jack stands and had to remove the cross member/transmission support. Being able to move then tranny up and down made a huge difference, and adjusting the tranny position so everything lines up is just as important, I also needed a second set of hands when attaching the cat to the manifold.
 

rgoldberg

Original poster
Member
Dec 13, 2011
35
continuation...
Drove 100+ miles with no issue then ont he way home flagged these codes, P1516, P2101, P0106, & P2119. Drove to work the next day, no issue, had a major rain storm, and the TB would start, she turned over, acted like she was going to start but didnt.
I wish i could remember if i hear the fuel pump spinning up, but i dont. Got to work the next morning and she still wouldnt start but I swear I heard the Fuel Pump running. I wiggled every fuse and relay in both boxes, then check all the connectors on the front and top of engine and she fired up. I let her run for a but 10 mins, not issues but a Check Engine Light. Fired her up about 2 hours later, no issues. Fired her up 2 hours after that and CEL went out and she home just perfect.

Today I got my OBDII Sensor and Torque Pro and Car Guage PRo and pulled 2 codes, but no CEL, and only P2101(current) and P0106(pending).
I ordered a new Manifold Pressure Sensor.
Maybe that will help with P0106, but what do I do about P2101?
I cleaned the TB last week when I replaced the Cat, and I never disconnect the battery, then I got the P2101 code and I disconnected the battery, all seems right until it came back...2 times now.

Any advice on the next step?
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
You should disconnect the battery anytime you clean the throttle body. So disconnect it for 30 minutes to reset things and see what happens. P2101 is more concerning as this relates to the throttle motor performance and may throw you into REP mode and may need to be replaced. We'll see after the reset.
 

rgoldberg

Original poster
Member
Dec 13, 2011
35
I did disconnect the battery, the day before it died at work, that was Tuesday. Code for the TAX and MAPS came back. Found a TB that said for this vehicle you have to keep clearing the fault until it doesn't return.
My buddy came iver with his tech2, cleared the fault a few times as the vehicle ran, we'll see what happens when I drive to work tomorrow
 

rgoldberg

Original poster
Member
Dec 13, 2011
35
Drove in to work today, 48miles, only code was the MAP, P0106 Manifold Absolute Pressure, and it only seems to set at speeds greater than 65 or 70mph. When I arrived at work I installed a new MAP sensor.
The P2101 Throttle Actuator Control Motor Circuit Range, has not returned.
 
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