I replaced the two upstream O2 sensors last weekend and the downstream are being installed this weekend. When I went to the muffler shop to get one of the sensors loosened up, the muffler shop mechanic told me that my cats were clogged up (less than 50 degrees between front and back).


So my question is, should I get just the new cats or the entire Y pipe for my 2004 Disco II? What is the advantage of replacing the Y pipe (if there is one)?


Either way, what is a good place to get them? I would like to get the low restriction high-performance version if at all possible.


Also, I apologize for posting another cat question but after looking through these forums I found a lot of posts that are almost a decade old.

 

How did the guy at the muffler shop determine the cats were clogged? If it's not throwing an engine code then I wouldn't touch them until it causes an issue or an engine light.

With replacing with a new y-pipe you get a cleaner fit and will end up flowing better, but weld in universals will be cheaper.

 

They used an infrared thermometer and said that the temp on the upstream side is supposed to be 100 degrees cooler than the downstream side of the cat. If there's little difference in temperature then the cat is clogged and not doing its job.

Side note: Not sure if this is from the cat, but I did get the P1170 code tonight as I was driving home. My ultra-gauge had said I had a P0139 pending, but it went away. Should I just replace the downstream O2 sensors and see if that helps? I've only owned the car for 3 weeks and I have a pretty good hunch that the previous owner wasn't as proactive as I plan to be.

 

I live in a state that is governed by federal emissions and doesn't require smog testing (Alabama), and I ordered a set of the magnaflow non oem ones off of eBay for around $560 them had em ceramic coated to try and help with the temps. I would say just order a new y pipe personally BC you know you don't have to worry about rust that is already there. Keep in mind before I bought a new set, I had to spend around $70 to have a muffler shop weld up the top part of the drivers right before it connected to the manifold due to rust. The magnaflows are great and it even sounds a bit better but my worry was that it wasn't a fully welded piece, you had a band where the y came in from the passenger side. If you do get a new y pipe, keep the bolts out of your old one!!!! I learned the hard way but I did get $120 for the old cats at a scrap yard.
My set of federal emission non oem magnaflow y pipe after the ceramic coating while they were baking.

 

Unfortunately, Tennessee (Nashville and surrounding area) requires emissions testing so I will need one that passes those standards. That said, where can I find one like that? I'm not brand loyal, I just want one that works, fits and doesn't make my disco sound like a frickin dragster or diesel F250 dually.

On a side note, I've been getting codes P1170 and P0307. I know that 307 is a misfiring cylinder 7, but could a clogged cat be causing both of these issues?

 

If you have a misfire you need to fix that before installing new cats. Misfires cause quite a bit of damage including the roasting of catalytic converters.

 

Where should I start looking for reasons the misfire is happening? I've run Seafoam through the gas tank and induction cleaning. Still learning all this stuff so that may not have anything to do with a misfire.

Should I get new plugs and wires?

 

the misfire could be a loose connection or bad wire or plug. The federal emissions magnaflow non oem cats will pass smog test in all states except California and New York.

 

Ok. Will check the wires and plugs tonight to make sure they're clean and fitting snuggly. Should I replace the plugs as a safe measure? The previous owner kept most of his paperwork and I can't see anything about new plugs. He got new gaskets at 86k and cylinder head kit 3 years ago. Other than that it's been oil change and coolant flush.


That's good to know. I will start looking at a new one for after I get the misfire issue is solved.

 

couldnt hurt anything. I go with the factory recommended champion ones but everybody has their own preference. You can always crank it and pull the wire off to see if it's sparking or use a spark plug tester on the wire