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Discussion Starter #1
I keep reading that these TC sensors fail all the time and are expensive but needed if you keep the cats. Now if there are one in each cat and one in the exhaust you have 3 sensors that can cause these to light up and even cause a shut down…

Some have said that removing the cats is a solution and a good one to me because your removing restrictions and increasing power so there are two positives to it.

But you still have one on the exhaust. So if you install a Tubi exhaust do you still have a sensor ?

Now could one bypass the sensors with a switch to turn them off when they act up ? Also install 3 racing temp sensors with gauges inside to monitor operating exhaust temperatures ?

Now one step further when modifying the exhaust would be to when installing replacement pipes for the cats, one could get them tapped for these sensors and have the Tubi tapped as well (if not tapped in the first place) this would seem like a good solution to remove this problem and have a solid reading of operating temperatures.

Let me know what you guys think???

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good idea

great idea and more power...anyone kmow whether this would work or not / and does it pose a problem to the engine and ecu? i have a 355..

matt:drive:
 

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TCs

Quick reply because I have to run...... Tubi mufflers do have the tap for the third TC. And you cannot disconnect the TCs because it instantly sets the slow down light. More later. -Steve
 

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Discussion Starter #4
whiteNSX said:
Quick reply because I have to run...... Tubi mufflers do have the tap for the third TC. And you cannot disconnect the TCs because it instantly sets the slow down light. More later. -Steve

Steve, if the Tubi has a tap for the 3rd TC, couldn’t you tap the other two temp wires to it? (I don’t know what the wires look like, so I’m assuming you could).

Or another alternative would be to reroute all 3 original temp wires to something else like water temp to kind of fool it with another reading and then use racing temp sensors to the cats/replacement pipes and another to the Tubi/original exhaust?

In my experience, I know computers can be fooled and any type of sensor can be installed on an engine to monitor critical components. My question is this, what else would be attached (electronically) to this sensor to prevent or make it extremely difficult to bypass?

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Slow Down Light

I've got a little more time now, so let's examine a couple of possibilities.

One is that the light is correct, and the converters are getting real hot. This almost always occurs when the engine has a misfire, and dumps raw fuel into the converter. They can turn bright red, and internally melt into a big ball. Melted converters rattle and fail to work properly. New converters cost - are you ready - $4,000 each from the factory, and there are two on an F355. Unbelievable. (However, there is a source in California that makes good copies using a Magnaflow brick, selling for $328. They work just fine.) So, it would be nice to have a light that functions correctly.

As for moving the TC locations, the easiest way to fake out the ECU would be to move them to the inlet side of the converter. A properly working TC would never send a nasty signal to the ECU, because it is the outlet that gets super hot.

Your original thread brings up the possibility of gutting the converters. Unless you have an early 1995 F355, you can't do it. Late 1995 355s and on (USA cars) have OBDII, which is On Board Diagnostics Two. The converters have an oxygen sensor on the inlet and outlet. The ECU looks at the output from both and determines whether the converter is doing its job. If you gut the converter, both sensors would produce the same signal, and the ECU would set a "Check Engine Light". There is an aftermarket piece available for Camaros, Corvettes and Mustangs to fake out the ECU, but I don't know how to do it on a Ferrari. And there's always the ethical question of removing converters, but that's a discussion for another time. Good catalytic converters cause very little backpressure increase (you can see straight through them), so the hp increase would be negligable.

OK, what if the TC is sending a bogus signal to the ECU? I know that you can't just unplug them - you get a solid Slow Down Light all the time. Physically, TCs are held into the converter with a fitting that resembles a Swagelock fitting that is welded in , and have a stainless braid extending to the wire connector. I believe there are two different length TCs, one is much longer than the other two. On the bench, I could not determine any difference in the three, even though I knew one would intermittently give a false signal. One possible solution would be to plug the hole in the converter and just let the TC dangle in the air. Another was one I was about to try, but the owner sold the car in order to pay for his new F430, so I never got to try it. I was going to buy one TC, the one with the long wire, and try it in each position until the slow down light went away. For $150 and a little time, the fix would be (semi)-permanent, and wouldn't require any modifications to the car.

And BTW, the converters are not so easy to get off on an F355. You can unbolt them, but there is no hole big enough to get them out. You have to remove a bunch of stuff to create one.

I've left a lot of details out of this reply, so if you have more questions, feel free to ask.

Steve Julius
Automotive Instructor
Automotive Technology Department
Mesa Community College
Mesa, Arizona
 

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Discussion Starter #6
Well for me it would be for a 348 (91-92) with cats removed because they can produce more hp, now you wont get 50 bhp but you could get up to 5-10 more maybe a total of 25-30 with a Tubi. Being a pre 95 this would also remove issues with the OBDII. As far as the ECU goes, would this still be an issue with the “Check Engine” light on a 348 ? Could disconnecting the battery for a while then restart it and let it reset itself ?

There has to be a solution to this with an additional stand alone temp sensor for true readings

Now I have not measured it on a dyno as far as hp gain but in I did see these on American muscle cars (Stang’s and Vette’s). So I’m assuming it would be close. Now another issue would be the size of the honeycomb in a Ferrari cat but in my experience they are quite small and do create some backpressure and when removed, helped with low end torque.

And yes, as far as the ethical question about the converters, that's a discussion for another time

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Pre-OBDII cars are a different animal. You can gut the converters without any adverse effects on the ECU. The ECU has no way of knowing, so no check engine light. Also, on OBDI cars, you can always clear any codes by disconecting the battery for 30 seconds. This is not true on OBDII cars - most of the time (but not always), you need a scan tool of some kind to clear the code. An outfit named Autotap makes a great program for a laptop that lets you look at the datastream of the ECU on OBDII cars. Pretty handy for all kinds of diagnostic work, and for clearing codes.

As for the TC, I'm sure there is some way to defeat the ECU, but I don't plan on taking the time to figure it out. My car is a 1986 with one cat and one TC. If it screws up, I'll just replace it. Sounds like a good project for you to work on :)

I won't argue with you about 5hp or so gain by gutting converters, I'm just not sure you could ever really tell by seat-of-the pants on the street. BTW, early muscle cars came with pellet converters, which were terrible. The new substrates are pretty good.
 

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Discussion Starter #8
I guess my thoughts were right then, because when I was looking at engine mods for the 348 (exhaust/induction) it said engine chip for 355 and up so I kind of figured it had some kind of computer on board.

It’s good to know that on pre OBDII cars the cats can be removed without affecting the ECU. So this means the TC’s can be removed/disconnected, and two racing temp sensor installed on both end of the replacement cat pipes to monitor exhaust temp without any problems…does this sound right, I know it’s talk and on paper now but what do you think?

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I said that you could gut the converters without messing up the ECU, but I didn't say you could remove the TCs. My 1986 car still has a Slow Down Light, so the TC has to be there. Now, if the converter is gutted, the TC is not likely to get real hot, so it will probably never set the light. But if the TC itself goes bad, you can still get a light.

BTW, a TC is a little different than a variable resistor sensor. A TC is made of two dissimilar metals, probably in this case, one wire is chromel, the other is alumel. Where the two wires touch, which is in the tip of the TC, a small voltage is generated depending on how hot the junction is. The ECU looks at the voltage and converts it to a temperature. A good explanation can be found at http://www.picotech.com/applications/thermocouple.html That is why I think it would be more difficult to bypass a TC. Am I making any sense here?

Steve
 

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Discussion Starter #10
After reading the link on thermocouple’s I understand better what you mean about having to keep the TC’s connected to provide info to the ECU. So my original question on my first post was TC’s fail quite often and are expensive to replace and was there a way to bypass them. So I guess the question is no unless getting a modified ECU.

Does this sound right?

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Nothing is impossible, but it sure would take some effort. I suppose one could build a small millivolt generator that would send a signal to the ECU. Or, I'm pretty sure it is a standard K-type TC, so you could try buying one from a US supplier and hope it is more reliable. For me, it's just not worth the time involved. -Steve
 
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