F355 Cylinders 5-8 cutting out

Okay.........this has happened a couple of times now. Slow down 5-8 warning light coming on and cylinders 5-8 are shutting down, so that I can barely "limp" along.

Here is what I think I know....if I'm wrong, or you can add some helpful hints, please do:

Three things are possibly happening:
#1: The catalytic converter for cylinders 5-8 is overheating and therefore shutting down those cylinders in order to protect the engine. (I have owned enough Ferraris to know that the likelyness of this is about 5%)

#2: The ECU for cylinders 5-8 is faulty and is occassionally "freaking out" with no rhyme or reason, telling itself that the catalytic converter for cylinders 5-8 is overheating, and then shutting those cylinders down. (My guestimation of the odds for this is about 85%)

#3: The thermocouple on the tail end of the catalytic converter for cylinders 5-8 is faulty, and occasionally sending a faulty signal to the ECU that it is overheating, thereby making the ECU shut cylinders 5-8 down. (My guesstimation of the odds for this is about 10%)

Now, in order to confirm my feeling that #2 is what is actually happening, I want to swap the cylinder 1-4 ECU with the cylinder 5-8 ECU and see if cylinders 1-4 now start shutting down. If this is the case, then I have a faulty ECU. If cylinders 5-8 shut down after the swap, then the thermocouple for cylinders 5-8 is faulty.

If my car starts on fire, then the catalytic converter for cylinders 5-8 was actually overheating!

Now, I have removed the side covers from the engine bay in order to locate the ECU's so I can swap them. I am assuming that the "braided wire" coming from the thermocouples on the back ends of the catalytic converters goes up into the ECU's. There are various wires and harnesses and plugs, etc., back there and the braided wires go way back underneath a bunch of other stuff, and I'm not sure what exact part IS the ECU and also, what to take off / disconnect to get at it.

Anyone have any photos, schematics, etc. that shows where the ECU's are exactly and how to get at and remove them, so I can swap them?

Please help!

 

Here's a schematic view. In the diagram the ECU's are the grey shaded squares numered "26".

Access the left hand ECU from within the engine bay, having removed the left hand side cover

The right hand ECU is accessed from underneath the vehicle, not far from the exhaust system

Mine are black and are about the same size as a packet of cigarettes
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Well,

Thanks for all the posts regarding my problem. The exhaust ECU's are below and tucked way back in towards the rear quarter panels from the other wiring connectors, etc. that you see when you remove the side covers in the engine compartment. They have two 7mm nuts holding them on. Remove the nuts and they slide off of the two long threaded studs. Unplug the two
connectors from them and voila, they are free. I cleaned all connections with electrical parts cleaner before swapping them.

Now, if I get the slow down light "cut off" of cylinders 1-4, I know that the ECU is bad. I went for a test drive, and so far, no problems. If the same 5-8 slow down light comes on, it will either be a bad thermocoupler on that cat, or
my cat is actually overheating (which I doubt, but, you never know).

Jeff