How to change the catalytic converter TU3JP(KFV)

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My Name: Ozvtr

Posts: 942
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
Has thanked: 36 times
Been thanked: 252 times


If you have been following my trials and tribulations you will know I have been "fixing up" a petrol powered 2003 C3 that has has a few
What is a catalytic converter? Basically it converts harmful exhaust emissions into harmless or less harmful byproducts. It's a roughly cylindrical device that sits in the exhaust system just outside the engine. It contains a fine "honeycomb" ceramic material.
One thing that I noticed straight up when I got the car was that the catalytic converter was not stock. Not a big deal in of itself but the LEXIA scan tool showed a P0420 error "catalytic converter aging loss of efficiency"
cat 001.jpg
The computer takes data from the oxygen sensor positioned in the exhaust pipe just after the catalytic converter to determine the performance of the catalytic converter. The output of this sensor is usually a constant voltage of about 0.4 of a volt.
cat 001a.jpg
This is a snapshot of a LEXIA scantool page. The two traces that we are interested in are the ones labeled "upstream" and "downstream". These traces were taken over about 15 minutes and represents a trip down the highway. In the beginning the engine is cold and nothing happens until we get to about 200 seconds. Then the engine management unit starts enriching and leaning the fuel every few seconds. This is normal and you can see the output of the upstream oxy sensor oscillating by about a volt as the mixture is enriched and leaned by the computer. Now, I am not going to go into how a catalytic converter works but the oxygen output of the catalytic converter should be constant. So the voltage from the oxygen sensor should therefore be constant too. However if you look at the downstream oxy sensor you will see the converter is doing nothing. Whatever is going into the converter is coming out the other side.
Another hint was that the exhaust had a "tiny" note to it. What does that mean? Well most exhausts are made of tubes of steel typically of about 40-50mm (inch and a half or so) internal diameter. This causes a restriction and slows down the compression waves of the exhaust from the engine. If you increase this diameter it is less of a restriction and these waves can "bounce around". You get this sound in exhausts that have deliberately been enlarged for better exhaust flow. Hmm was the catalytic converter empty and causing the tiny note?
Now theoretically a converter will not wear out. However the fine honeycomb can become blocked or the active surface can become coated in impurities from the petrol or oil. So they can fail.
Well it looks like mine has failed so let's get it out.
cat 002.jpg
I jacked up and supported the car at the front drivers side.
cat 003.jpg
cat 004.jpg
I removed the heat shield.
cat 012.jpg
cat 013.jpg
cat 014.jpg
I disconnected and removed the downstream oxy sensor electrical connector.
cat 008.jpg
I loosened but did not remove the nuts holding the converter to the exhaust manifold. This required a deep socket and two long extension bars then the jack handle onto the ratchet handle! They were tight!
cat 010.jpg
I loosened but did not remove the bolt holding the exhaust bracket to the engine block.
cat 011.jpg
Next I completely removed the bolts holding the flanged exhaust coupler.
If you look at the photo the springs are on the wrong side of the flange. This is the front side they should be on the back side. The bolt and spacer cup are installed the correct way but they should be up against the flange not up against the spring.
I then removed the bolt holding the bracket to the engine block, then removed the four nuts holding the converter to the exhaust manifold. Now the converter will come out.
cat 016.jpg
cat 018.jpg
Well, Well, Well! A comparison of the two "converters". The one fitted to the car has no substrate (element) in it at all! It's just hollow! The OEM converter is from my donor wrecker car and shows the honey comb construction of the substrate. You can also see that the overall construction of the OEM converter is much better.
I then installed the "new" converter. Installation is just the reverse, no real traps.
cat 015.jpg
The spring clamp bolts holding the flanged coupler together were different to the ones that I took of my donor car. The arrangement of the dome shaped seal on the exhaust pipe was a little different too. I could not put the short spring arrangement onto the flange when it came time to bolt it all back together as there was no spring tension holding the joint together. The spring is too short (or the bolt is too long?). I can only assume that the aftermarket 'cat' came with it's own set of springs and bolts? Another thing to note are the nuts. The nuts on the exhaust of the car had nyloc nuts on them and the OEM nuts were clinched. Now clinched nuts are basically a normal nut that's been deformed slightly to clinch onto the bolt's thread. Nyloc nuts have a nylon insert to grab the thread of the bolt. Both types resist undoing by their respective clinching mechanism. HOWEVER, how long do you think the nylon insert will last with the heat of the exhaust? Yep there wasn't much nylon left.
Ok, let's see what the downstream oxy sensor says now. Start the car up and put the LEXIA on it.
The down stream oxy sensor is sitting at about 0.8 of a volt. A bit rich but the engine hasn't been running for long, still a bit cold. You can see that the worst case is it fluctuated by about 0.06 of a volt just at the end. Yeah! Looking good.
The engine management unit determines if the catalytic converter is not performing and turns on the check engine light. The thing is that I can not tell you what criteria it uses to determine that. I can only say that the output should be a flat line at about half of a volt. If it's a reasonably flat line then the cat is doing something! It's only if the output begins to oscillate that you can see that the cat is not working.
Each time I fiddled with things like oxy sensors and then reset the engine light, it would take a day or so to come back on, not straight away.
So What happened? I have no idea! For some reason 'they' replaced the OEM cat. Did the replacement have an element in it? Did the replacement element break (or something)? All I can tell you is the check engine light would have been on while there is no element in the converter.
Did they do it to get more power? Hmm the TU3 engine is not what I would pick to soup-up! That would be like having the worlds fastest's still a snail! The increase in power would be small if at all. The plugs and exhaust weren't sooty so the air fuel ratio was OK.
Here in Queensland Australia we don't have MOT. We do have safety certificates that are performed and issued on the transfer of title (sale). There can't be any 'lights' on the dash, that's a fail! So how did I get away with it? Pure ass!!! I honestly did not know about the cat at the time and I was having troubles with the oxy sensors failing (open circuit and heater failures). I reset the engine light and it stayed out during the inspection! It came on a day or so later.
The catalytic converter is a very expensive thing to replace considering your car will run just fine without it. If your cat fails you can put a sleeve on the downstream oxy sensor, the sensor is no longer in the exhaust stream and so it gives a steady output. It's possible a tech doing the MOT might spot it and that might attract a fine or in the very least a fail...I don't know.
The catalytic converter is there to reduce the pollution that your car produces. Think of your civic duty if it fails on you.
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