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Discussion Starter #1
I am scheduled to have both my cats replaced because the left side cat has gone bad. I am replacing both sides with hyperflow cats.

My mechanic now refuses to replace the damaged side cat without replacing the exhaust manifold, due to the last customer he had where he had replaced the cat only to have it fail again due to a leaky exhaust manifold. It is possible that a cracked manifold can send more air into the 02 sensor thus causing the fuel mixture to be richer, thus more unignited fuel into the cats which damage the cats.

I asked him if a leakdown test would give any indication of a leaky manifold, since I had one performed prior to purchase last year. He responded that the leakdown test just encompass the internal parts of the combustion area, anything past the exhaust valves are anyones guess or careful inspection.

Now I am faced with an additional expense of replacing the one side manifold on top of the cats.

Any insight on this, or suggestions. I need some more info before giving the OK. This expense had put a huge dent on my budget this year :(
 

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why wouldnt he be able to take the exhaust mani off and inspect it. that way if it is NOT cracked. you can just pay for a remove and install. just pay for new ex mani gaskets. i can imagine an ex mani for a ferrari being kinda pricey. if a factory mitsubishi eclipse turbo ex mani is damn near 300 dollars from the dealership.


Eddie Rosado
 

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I am scheduled to have both my cats replaced because the left side cat has gone bad. I am replacing both sides with hyperflow cats.

My mechanic now refuses to replace the damaged side cat without replacing the exhaust manifold, due to the last customer he had where he had replaced the cat only to have it fail again due to a leaky exhaust manifold. It is possible that a cracked manifold can send more air into the 02 sensor thus causing the fuel mixture to be richer, thus more unignited fuel into the cats which damage the cats.

I asked him if a leakdown test would give any indication of a leaky manifold, since I had one performed prior to purchase last year. He responded that the leakdown test just encompass the internal parts of the combustion area, anything past the exhaust valves are anyones guess or careful inspection.

Now I am faced with an additional expense of replacing the one side manifold on top of the cats.

Any insight on this, or suggestions. I need some more info before giving the OK. This expense had put a huge dent on my budget this year :(
I don't know if this is still an issue for you since your post is quite old by now. Anyway, how do you know the cat's gone bad? Was it an emission test? The fact that the mixture could be biased due to leakage shouldn't damage the cat permanently. What it could do is damage it's catalytic performance momentarily since the mixture has to be lambda 1 for it to work as a 3-way catalyst.

I agree to the advice to have the exhaust checked and if they got to then remove it first. If you're on a tight budget then why pay for something that may turn out to be unnecessary?

Please come back with the end to this story.
 

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I've found this product to work wonders for cleaning out the cats.
 

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Your mechanic is right in that the leakdown test would have in no way indicated a leaky exhaust manifold. The only way to tell that is to visually observe the crack or hear and feel exhaust gases escaping. The exhaust system is under pressure so I wouldn't imagine extra oxygen entering to fool the O2 sensor but I guess anything is possible.

At any rate, you will need to get the manifold fixed at some point so it might as well be now. What I would look into is pulling the manifold and seeing if there is anyone around that can weld up the crack for you.
 

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Discussion Starter #8
I don't know if this is still an issue for you since your post is quite old by now. Anyway, how do you know the cat's gone bad? Was it an emission test? The fact that the mixture could be biased due to leakage shouldn't damage the cat permanently. What it could do is damage it's catalytic performance momentarily since the mixture has to be lambda 1 for it to work as a 3-way catalyst.

I agree to the advice to have the exhaust checked and if they got to then remove it first. If you're on a tight budget then why pay for something that may turn out to be unnecessary?

Please come back with the end to this story.
I had the check engine warning light constantly on so I brought it to the local ferrari dealer for a diagnostic. Results indicated a faulty left cat.
 

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I had the check engine warning light constantly on so I brought it to the local ferrari dealer for a diagnostic. Results indicated a faulty left cat.
I see. Well, lets hope then that they did their catalyst diagnosis calibration the right way. :) Do you have a -> '97 with Motronic 2.7 or a '97 -> with 5.2? What milage do you have and do you know the history of the car well?

Have you dicided how to go about it yet? Have you got a price for changing the manifold as well or for just inspecting it?

Finally, if you don't mind, how much will the double cat job be?
 

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Discussion Starter #10
I see. Well, lets hope then that they did their catalyst diagnosis calibration the right way. :) Do you have a -> '97 with Motronic 2.7 or a '97 -> with 5.2? What milage do you have and do you know the history of the car well?

Have you dicided how to go about it yet? Have you got a price for changing the manifold as well or for just inspecting it?

Finally, if you don't mind, how much will the double cat job be?
I am not so sure what version mototronic I have, but can check records later. I have about 22K miles on it.

I am not taking it to the local ferrari dealer but to a garage that works on italian supercars. I am not replacing the cats with the originals which will cost around 2.2K each, but instead I am getting hyper-flows at about 1.2K each.

I believe they quote me at $6.5-7.0K for replacing both cats and the manifold.

I have all the copies of the previous 2 owners work that has been performed on them. Seems the left manifild has already been replaced. Don't quote me yet on the side, but I can check records when the nitty gritty comes along.

I am still waiting on the check the previous owner is sending me to help compensate for the repairs.
 

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Pete, if you are going to replace the exhaust manifold and just junk the old one, send the old cracked one to me. I'll pay the postage. I'd like to see if I can repair it. Just a little welding project for me, I figure if it is already broken I can't make it worse.

Best case I successfully repair it so it passes a magnaflux and pressure test and we have it for the next 355 member with a cracked manifold. Worst case I completely ruin a manifold that was already junk.
 

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I would have them unmount the manifold and have that checked first. If its broken, change it and see if you still get the cat diagnosis code. After 22k the cat shouldn't have gone bad (at least not only the cat) so I think it might be that you could do without replacing the cats if the code is set due to a problem with the manifold. But then you don't get the hyperflows of course... It's still worrying if the manifold already have been replaced once. :(
 

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Discussion Starter #13
I would have them unmount the manifold and have that checked first. If its broken, change it and see if you still get the cat diagnosis code. After 22k the cat shouldn't have gone bad (at least not only the cat) so I think it might be that you could do without replacing the cats if the code is set due to a problem with the manifold. But then you don't get the hyperflows of course... It's still worrying if the manifold already have been replaced once. :(
Now you have me wondering if that faulty code from the cat is just from the leaky manifold. Although if logic follows, once the sensors first sensor in the cats detect more air in the system, it would send a signal to the injectors to provide a richer fuel mix, thus causing unburned fuel into the cats which may damage the cats.

Does anyone have any other scenarios you may think of.
 

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Now you have me wondering if that faulty code from the cat is just from the leaky manifold. Although if logic follows, once the sensors first sensor in the cats detect more air in the system, it would send a signal to the injectors to provide a richer fuel mix, thus causing unburned fuel into the cats which may damage the cats.

Does anyone have any other scenarios you may think of.
Yes, it can be the case. The thing is that the catalyst diagnosis is not "an exact science" but is a functionality in the engine management system.

If I'm not totaly wrong on the configuration of the 355 it uses the signals from the oxygen sensors (one in front and one after the catalyst) to judge the performance of the catalyst. In order to be legal you have to turn on MIL (malfunction indication light a.k.a. check engine) if the emissions are higher than the corresponding emission standard levels.

From that point of view, as an engineer at Bosch (which I believe did the job on the 355) you want to be sure that you turn on MIL for all catalysts that generates higher emissions than are legal in order to avoid for example recall on sold cars which is about the most expensive thing in the world. On the other hand you don't want to turn on MIL if you are not sure that the catalyst actually is malfunctioning. If you do, then you have a customer that has to have his/her cars at the shop and also pay for a new cat and that's no good will at all. Of course it would be even worse if they were to find out that it actually was unnecessary...

Anyway this is a bit tricky because when you do the calibration you do not have a lot of real world aged catalysts to do the calibration on. This leads to the calibration not being exact but as said a judgement of where to draw the line between a good and a bad cat so to speak. If you throw in the uncertainty of a leakage in the manifold you really can't tell if the diagnosis are working properly and is able to make the right decision if a cat is good or bad. That's why I suggested that you get the leakage sorted out first, the have your car reseted and then see if the cat code comes back.

Just some more reasoning: As you write if the sensor gets an extra dose of air then the EMS should react with injecting more fuel so that the sensor will detect the target lambda. That would then mean that the engine would run richer than wanted but the sensor (and thus the cat due to the extra air) would see the target mixture and it would probably not directly damaged the cat. The problem is if you have unburned fuel AND extra air coming into the cat and the combustion takes place inside the cat. Then the high temperatures would most likely damaged the cat and that may well be the case here.

even more blablabla: As someone else wrote in the thread you could expect to have a higher pressure inside the exhaust than outside and then no air would enter it. Unfortunately it in most cases is not as simple as that. If you run on idle or low speed and loads (which is where the most diagnoses runs) you do not have that high pressure and for sure you can have swirls in your gas flow that creates local areas with very low pressure giving air the possibility to enter.

Finally I'm not sure if I have made any sense or help to you. I apologize for being so fuzzy in my attempt to explain my view. :-( I guess the bottom line is this that I wrote earlier:

If you throw in the uncertainty of a leakage in the manifold you really can't tell if the diagnosis are working properly and is able to make the right decision if a cat is good or bad. That's why I suggested that you get the leakage sorted out first, the have your car reseted and then see if the cat code comes back.
 

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Discussion Starter #15
FF

I totally understand your reasoning on performing a check on the headers/manifold before replacing the cats, and or replacing the manifolds before replacing the cats. Unfortunately I am not experienced nor have the correct tools in performing such checks and would have to rely on a garage.
This said garage also charges a fairly reasonable labor charge as opposed to the local ferrari dealership in town. But this labor charge does not come cheap, and to have them take apart the exhaust system to check and or replace the manifold, put it back together and run another diagnostic can be a time and part (catalyst) saver at the least. Nevertheless, if I still get the faulty code then they would have to take down the exhaust system again to instal a new cat. Do you see my dilemna here.

As far as the swirling goes, and pressure in the exhaust system, I have no idea. That is delving into fluid/gas dynamics which is out of my realm of knowledge.

I will inform my mechanic about your suggestion and see what the options are. I will post further notes and progress. For now I will refrain from using the car until I have this issue resolved.
 

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Discussion Starter #16
Pete, if you are going to replace the exhaust manifold and just junk the old one, send the old cracked one to me. I'll pay the postage. I'd like to see if I can repair it. Just a little welding project for me, I figure if it is already broken I can't make it worse.

Best case I successfully repair it so it passes a magnaflux and pressure test and we have it for the next 355 member with a cracked manifold. Worst case I completely ruin a manifold that was already junk.
Sure, I can do that Pete. I'll send you a PM once I have the old one ready.
 

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FF

I totally understand your reasoning on performing a check on the headers/manifold before replacing the cats, and or replacing the manifolds before replacing the cats. Unfortunately I am not experienced nor have the correct tools in performing such checks and would have to rely on a garage.
This said garage also charges a fairly reasonable labor charge as opposed to the local ferrari dealership in town. But this labor charge does not come cheap, and to have them take apart the exhaust system to check and or replace the manifold, put it back together and run another diagnostic can be a time and part (catalyst) saver at the least. Nevertheless, if I still get the faulty code then they would have to take down the exhaust system again to instal a new cat. Do you see my dilemna here.

As far as the swirling goes, and pressure in the exhaust system, I have no idea. That is delving into fluid/gas dynamics which is out of my realm of knowledge.

I will inform my mechanic about your suggestion and see what the options are. I will post further notes and progress. For now I will refrain from using the car until I have this issue resolved.
You are absolutely right about the dilemma cause by the price factor. Sorry, I realise that I lost track into a more technical discussion than your question... :) Since you first stated that you wanted hyperflow cats it of course can be the wisest thing to replace them anyway and if needed also the manifold at the same time. Good luck and I'm sure it will work out well either way.
 

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New Inside...

Hi Pete.

Sorry to hear about your cat (s). I was recently faced with the same dilemma when I had my engine out a couple of months ago for beltchange. My local Ferrari mechanic noticed, what I feared when I bought the car, that both of my cats where really shot. The insides where no longer attatched to the actual cat and needed to be replaced. Luckily I had no problems with my manifolds and my mechanic suggested a slightly different approach than simply replacing them. He sent them off to a very nice workshop which opened them up and replaced the internal `stuff`with new made of stainless steel. He said it would last the lifetime of the car and I ended up paying roughly $350 per side. When I got them back I could hardly even see they had been opened and for me this worked out nicely. Also, as a bonus, the car still appears stock, for what its worth.

A friend here in Sweden with a 355 GTS had his manifolds go bad on him and, since this is a known problem with these cars, decided to have new made out of stainless steel. It did not come cheap but made for good value in both performance and sound. Plus, he will never encounter similar problems again. (I believe he payed something like $12.000 for both sides, but dont quote me on that)

Let me know how everything pans out and good luck:)

Uffe
 
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