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I have seen some posts re the Pre CATS, mine have a nasty (and annoying) rattle and i am thinking about removing them. It has just passed the MOT so all is fine for another year but any suggestions as the garage thinks they have started to break up inside?
 

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I have seen some posts re the Pre CATS, mine have a nasty (and annoying) rattle and i am thinking about removing them. It has just passed the MOT so all is fine for another year but any suggestions as the garage thinks they have started to break up inside?
What about the lambda sensors?
Will they work correctly? Any ecu errors?
 

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What about the lambda sensors?
Will they work correctly? Any ecu errors?
I removed the pre cats. Lambdas work as before, pre-cats dont influence them, they are located before them. Main cat is more than enought to pass emission test as well. (provided the engine is warmed up and the cat is in fine order)
 

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It will take longer for the main cat to reach 'light up temperature', but the engine will make more power and torque.:D
 

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Thanks for the posts - i will have a look over the weekend and see the state of the rest of the exhaust. Might look at replacing the manifold with the non cat version as it seems it will still pass the all important MOT.
 

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Thanks for the posts - i will have a look over the weekend and see the state of the rest of the exhaust. Might look at replacing the manifold with the non cat version as it seems it will still pass the all important MOT.
Removing the cat will not influence the lambdas?
 

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We refer to the front lambdas as pre-cat sensors. They measure the oxygen content of un-catalysed mixture (even if they are after the pre-cats). The pre-cats are there to raise the gas temperature and to start the chemical reaction. The main cat is there to perform the function of a catalytic converter.

Because the gas properties have changed due to main cat, the rear sensor should produce different readings to the front sensors (it does). Removing the front cats for a more efficient manifold will not impair functionality other than delaying the temperature and time the main cat takes to become hot enough to support catalysation.
 

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We refer to the front lambdas as pre-cat sensors. They measure the oxygen content of un-catalysed mixture (even if they are after the pre-cats). The pre-cats are there to raise the gas temperature and to start the chemical reaction. The main cat is there to perform the function of a catalytic converter.

Because the gas properties have changed due to main cat, the rear sensor should produce different readings to the front sensors (it does). Removing the front cats for a more efficient manifold will not impair functionality other than delaying the temperature and time the main cat takes to become hot enough to support catalysation.
There si one thing I do not understand. Lambda sensor is actually an oxygen sensor. Does main cat affect oxygen levels? If it does it will actually change the readings of the rear sensor. What I do not understand is how different rear sensor readings would cause ecu error. I mean the sensor would send different info to the ECU but it would only mean a different mixure. Please correct me if I am wrong?

I know i am a pain in the ass and I appologize but I really need to figure it out for myself coz one garage tells me I need to buy new main cat, the other carage tells me I need to buy new rear lambda sensor and I do not want to throw money away just because I am ignorant as far as my car is concerned.

Thank you in advance for your patience.
 

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You're not a pain.
Yes, catalytic converters change oxygen levels. They help convert oxygen (O2), carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx) to water (H2O) and carbon dioxide (CO2).

The waveform for the front sensor should be constantly changing between about 0.7 and 1.5 volts. (1 volt being the centre hopefully) The waveform should be quite erratic. Because of this, the front sensors constantly adjust the fuel trim many times per second. However, once it all goes through the main cat, it should all even out into a steday flow of H2O and CO2 with only a very little O2. Because of this, the waveform for the rear sensor should really be a flat line of about 1 volt steady.

The management system records a code if the rear sensor produces an appreciable waveform. It could be because a front sensor is switching slowly and causing a fuelling error, or the main cat is damaged and inefficient. It is another way of controlling emissions more tightly and it is legislation for Euro 3.

In your case, the last thing I would expect you to need is a new rear lambda sensor. If it produces a return voltage, irrespective of the voltage waveform, it is probably ok. It is far more likely to be a cat or a front sensor (even if the fault code description says rear sensor fault). The only reason to change a rear sensor is if the heater element is burnt out. It takes a competent diagnostic mechanic to interpret what is happening correctly.:)

The way to tell for sure is to connect the front sensors to an oscilliscope. If the both output a quickly changing waveform, it is the rear cat. If one or both change slowly, change the defective sensor(s).
 

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I have removed my front cats although off a gtv - and this has caused by eml to come on. I know others who this has not happened to tho. I am putting my cats back - the main dealer and other independents like alfaholics have siad to me that every car is different and that they cannot guarentee to be able to keep the light off if the change the front pipe without the cats. I would like to keep the cats off cos of the increase in power, unfortunately ive ordered them now and am havin them fitted tommorrow, so just be careful it seems wot may work on one car may not always on another
 

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You're not a pain.
Yes, catalytic converters change oxygen levels. They help convert oxygen (O2), carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx) to water (H2O) and carbon dioxide (CO2).

The waveform for the front sensor should be constantly changing between about 0.7 and 1.5 volts. (1 volt being the centre hopefully) The waveform should be quite erratic. Because of this, the front sensors constantly adjust the fuel trim many times per second. However, once it all goes through the main cat, it should all even out into a steday flow of H2O and CO2 with only a very little O2. Because of this, the waveform for the rear sensor should really be a flat line of about 1 volt steady.

The management system records a code if the rear sensor produces an appreciable waveform. It could be because a front sensor is switching slowly and causing a fuelling error, or the main cat is damaged and inefficient. It is another way of controlling emissions more tightly and it is legislation for Euro 3.

In your case, the last thing I would expect you to need is a new rear lambda sensor. If it produces a return voltage, irrespective of the voltage waveform, it is probably ok. It is far more likely to be a cat or a front sensor (even if the fault code description says rear sensor fault). The only reason to change a rear sensor is if the heater element is burnt out. It takes a competent diagnostic mechanic to interpret what is happening correctly.:)

The way to tell for sure is to connect the front sensors to an oscilliscope. If the both output a quickly changing waveform, it is the rear cat. If one or both change slowly, change the defective sensor(s).
Thank you very much. I will have a specialist test both my sensors and if they are ok I will get a new cat.
I will probably not be able to find an original alfa cat so are there any requirements for the main cat of Alfa 147 1.6, 105 hp, '01.
As far as I know this model has only one cat which is in the beginning of the exhaust pipe.
 

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I have had a look on the net, and I see your exhaust system is different. The 105BHP version is not common and it appears to only have one cat which is located just under the manifold where the other versions pre-cats are. I don't know if you have two pre-cat sensors or just one. I can't even tell if you have a post cat sensor, but I'm sure you do. I don't think your version is compatable with the others, and I don't think the de-catted manifold is an option for your car. Unfortunately, the CSC website is not working correctly, so I cannot access the information as to whether one is listed for your car. I have not found an aftermarket cat for your car yet, so it maybe it will have to be a genuine one (if it is faulty). I think the best we can hope for is a faulty front sensor.:rolleyes:
 

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I have removed my front cats although off a gtv - and this has caused by eml to come on. I know others who this has not happened to tho. I am putting my cats back - the main dealer and other independents like alfaholics have siad to me that every car is different and that they cannot guarentee to be able to keep the light off if the change the front pipe without the cats. I would like to keep the cats off cos of the increase in power, unfortunately ive ordered them now and am havin them fitted tommorrow, so just be careful it seems wot may work on one car may not always on another
when the pre-cats were removed, what was done with the lambda sensors?
iirc if ya earth the sensors, they read (to the engine management) as if everything is fine, which might solve your EM light problem?
 

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I have had a look on the net, and I see your exhaust system is different. The 105BHP version is not common and it appears to only have one cat which is located just under the manifold where the other versions pre-cats are. I don't know if you have two pre-cat sensors or just one. I can't even tell if you have a post cat sensor, but I'm sure you do. I don't think your version is compatable with the others, and I don't think the de-catted manifold is an option for your car. Unfortunately, the CSC website is not working correctly, so I cannot access the information as to whether one is listed for your car. I have not found an aftermarket cat for your car yet, so it maybe it will have to be a genuine one (if it is faulty). I think the best we can hope for is a faulty front sensor.:rolleyes:
the car has only one cat and 2 sensors (pre and post cat).
The cat is gone coz it was broken and now the cat pipe is empty.
I am thinking about fitting a universal cat or something and I need to know if there are some requirements for the cat of my model - number of cells or length or anything else?
 

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Discussion Starter #16
Just to give you an update on the situation with the rattle from the Pre Cats on the Alfa 147 - it appears that all it was was a broken engine/exhuast bracket. I did spot many "threads" saying that these cause strange noises and sure enough now it is removed all is well.

Thanks for the help and everything posted made for interesting reading - you guys know your stuff.
 

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the car has only one cat and 2 sensors (pre and post cat).
The cat is gone coz it was broken and now the cat pipe is empty.
I am thinking about fitting a universal cat or something and I need to know if there are some requirements for the cat of my model - number of cells or length or anything else?
I'd just get a cat that fits...:rolleyes:
 

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I am also considering to change the exhaust system on my 2002 JTS to a Supersprint system, but it appears that there is much difference in the exhaust systems of phase 1, 2 and 3.
See:


Phase1, 1 cat 1 lambda sensor in front of the cat


Phase2, 3 cats (2 in the manifold 1 after the manifold) and 3 lambda sensors (2 in front of the cats in the manifold and 1 after the 3rd cat)



Fase3, 2 cats (2 in the manifold not shown) en 4 lambda sensors (2 in fornt of the cat and 2 after the cats)

Can anybody tell me why the "main" cat has been removed on my car model? My car has only 2 cats in the manifold and 4 lambda sensors (2 pre cat and 2 post cat)

I have searched the web, but is seems that Supersprint does not have a cat replacement for a JTS.
I noticed that my exhaust sustem does not match EPER
When I look in EPER I see the following 156 2.0 JTS '02:


no 1 and 15 are cats, however I do not see how to assemble pos 15 to pos 10...




However I only have 4 lambda sensors and 2 cats in stead of the shown 5 sensors and 3 cats (4 sensors in the first 2 cats , 2 left and 2 right, 1 after the next cat).

When I look at a GT JTS, it looks more like it:

no 2 is a flexible joint.



As far as I can see it looks like the Supersprint cat replacement is a substitute for the 3rd cat (POS 15).

Are there any more JTS owners who have a exhaust system such as mine?
Does anybody have experience with a high flow sports cat in a JTS?

What to do when I remove the manifold and replace it by a Supersprint system?

F156
 
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