Exhaust blockage / Cat failure

[sprucewood]

The 02 Exp. runs fine at idle since we replaced the intake, the PCV valve, idle air control sensor, throttle position sensor, new plugs. As we increase the RPM's via the throttle body it begins to bog down as if there is a lack of air entering the air intake system. We removed the air filter with no change in symptoms stated above. We pulled the EGR and pipe from below the exhaust header and checked for any blockage and replaced still no change. Could the cats have come apart causing a flow restriction out the rear exhaust pipe. ???? Please remember it idles just fine under a no load. Load it up above 2000rpm and it bogs down. Drove it around the block once and no power. Put in park and it idles near perfect. HELP HERE PLEASE

 

[JW]

I had similar symptoms and traced it to a failed driver's side upstream cat; it had completely disintegrated and blown down into the third cat.

 

[ROBinGa]

Sounds just like my symptoms of failed cats

 

[sprucewood]

I had similar symptoms and traced it to a failed driver's side upstream cat; it had completely disintegrated and blown down into the third cat.

By any chance did you have issues with your intake manifold ...melted holes or anything else ? My intake has melted holes down from where the EGR tube goes into the intake manifold.

 

[JW]

My problem stemmed from not having my EGR connected. I had put a Trick Flow manifold on (I have the 4.6L), which required mods to the EGR tube I had not completed. 3000 miles later, dead cat.

The EGR system reduces combustion (and, therefore, exhaust) temperature, which reduces/eliminates oxides of nitrogen (NOx). I don't recall the specific temperature, but over that temperature in the combustion chamber, NOx is created. I was running around without one entirely, but a malfunctioning EGR system could cause the same issue.

 

[sprucewood]

Before you replaced the cats, what were the symptoms of your engine ?
Was it "No power on excelleration" ? Did it idle just fine while sitting in park ? Im pulling my hair out here trying very hard to figure this out. I have replaced all sensors except Mass air flow and Coil pac. Thanks

 

[JW]

No power at all. Idled fine but would fall on its face at anything more than 20% or so throttle. And the deeper I got into it, the worse it was.

 

[sprucewood]

Your answer sounds just like what i am experiencing. Is there any way of diagnosing which cat has failed. I certainly dont want to start cutting out cats that may very well be good ones.

 

[JW]

Unbolt the works from the truck and inspect down each pipe. You can try the "hit it and see if it rattles" thing, but they're not hard to remove. You should see honeycomb in each upstream cat. My passenger's side was in tact, while my driver's side was an empty shell.

 

[sprucewood]

Ok thank you for your responses this late at night. First thing in the AM i'll be doibg just that. What bothers me though is this 02 XLS has only 74K original miles on it and this is happening.

 

[Gilligan]

I've run into that issue before and it wasn't the cat or an exhaust issue. Failure of the Mass Airflow Sensor or a leak after it will give those same symptoms. I learned this when I left mine not completely connected.

 

[sprucewood]

Unbolt the works from the truck and inspect down each pipe. You can try the "hit it and see if it rattles" thing, but they're not hard to remove. You should see honeycomb in each upstream cat. My passenger's side was in tact, while my driver's side was an empty shell.

HeyJw, i pulled the exhaust system from the headers to the flange that connects the muff. Looked into the front left 02 sensor hole and yes there is some cat dust and a few large quarter size pieces of the honeycomb cat that has come loose so i am going to buy two new "Walker" brand #81722 cats UNLESS you know of a better brand or something better, Ebay and Summit have them for $157.00 per unit. Whats your thought on this and also do you think these small pieces of cat material are responsible for the issue im having?

 

[JW]

Possibly. You wouldn't know for sure unless you cut the third cat away (and, like me, found all sorts of debris). You should be able to see the condition of each cat straight down the downpipes. If you don't want to cut it up, shake it and see how noisy it is.

 

[sprucewood]

Possibly. You wouldn't know for sure unless you cut the third cat away (and, like me, found all sorts of debris). You should be able to see the condition of each cat straight down the downpipes. If you don't want to cut it up, shake it and see how noisy it is.

Not much noise when i shook it. Passenger side is clean, no residue at all. Third cat seems ok also. What brand did you replace yours with and how much were they, where from ? Thanks

 

[JW]

I used the kit from Magnaflow. I got it at jet.com for close to what the non-California kit costs (California-legal kit is normally $1200, but I got mine for under $900). Because I don't live in a free state, I was limited on what I could get. Catalytic converters (aftermarket or otherwise) have to meet certain standards and carry a warranty, so any of them should be fine.

If the honeycomb still appears to be in place, this probably isn't your issue. I had golf ball-sized (and larger) chunks falling out, not just powder. My driver's side was a literal black hole - NO honeycomb at all visible in the downpipe. You could be on your way to a total failure, though.

 

[sprucewood]

I used the kit from Magnaflow. I got it at jet.com for close to what the non-California kit costs (California-legal kit is normally $1200, but I got mine for under $900). Because I don't live in a free state, I was limited on what I could get. Catalytic converters (aftermarket or otherwise) have to meet certain standards and carry a warranty, so any of them should be fine.

If the honeycomb still appears to be in place, this probably isn't your issue. I had golf ball-sized (and larger) chunks falling out, not just powder. My driver's side was a literal black hole - NO honeycomb at all visible in the downpipe. You could be on your way to a total failure, though.

Truck idles perfectly in park and when i put it in drive, its when i give some gas it bogs down. Engine is quiet, no odd sounds at all, not missing even under load.

 

[sprucewood]

Found it. Halaluya prayer does work.
.......I pulled the intire front half of the exhaust system out yesterday, emptied out about a quarter cup of catalytic granuals from the tube ends then today i brought out the leaf blower, placed my hand over one upper inlet tube and the blower on the other and turned it on. The rear cat was plugged completely as no air came thru. Air circled back around to where my hand covered the other tube inlet. Problem found and issue solved....finally. Searched the internet and found Calcat Rear converter from Magnaflow for $142.35 & free shipping. Thanks for all your input you guys.