Help with 355 "bogging down"

Was it the "slow down" light or the "engine check" light?

 

Sounds like a check engine like to me. I would pull the codes and see what they say.

 

Sounds like the cat converter electronic sensors are bad - have them checked and replaced if necessary about $300/each.
This usually results in overheating and lack of power at high end a relatively common problem.
Also, possible that the throttle cable is worn or stuck - about $175 to replace.

 

Sounds like the cat converter electronic sensors are bad - have them checked and replaced if necessary about $300/each.
This usually results in overheating and lack of power at high end a relatively common problem.
Also, possible that the throttle cable is worn or stuck - about $175 to replace.

 

Chris,

Slow down light issues (and all that goes with them) are one of the all time favourites on the forum (!). Best to get hold of a crate of beer and read all the threads you can stomach. Basically, the aim of the slow down system is to an alert to the possibility of an overheated catalytic converter. The thermocouples send a signal to separate ecu's (these are distinct from the main ECU in the cabin which ultimately processes info from all over the car). The cat ecu's linearise the voltages from the thermocouples and sends them to the main ECU. If the main ECU sees signals outside normal range, it energizes the slow down light. If the values suggest an elevated cat temperature, but not dangerously so, it sets a flashing light. If dangerously hot is indicated, the light is on permanently and the main ECU shuts down the bank of 4 cylinders on the hot side to prevent the cat converter going on fire.
That's simple enough. The problem is to find out whether the converter is actually too hot or whether some part of the system is faulty. A factor which makes things more difficult to analyse is that the slow down light (and the system) does not reset itself when everything has "cooled down". The error code is stored in the main ECU. You have to disconnect the battery and reboot the ECU each time you want to see if your last intervention has done the trick. Of course, the Ferrari dealer should have a diagnostic tool to read error codes and tell which component is bad, but we like to try to fix things ourselves!
So, your problem is one or a combination of the following:
1. An real engine fault which is causing the converter to overheat
2. Bad signal from thermocouple
3. Bad signal processing by one or both of the cat ecu's
4. Problem with the main ECU (your search will show that this was the case very recently).

I'm bound to have missed out something but with this rough outline you should be able to understand the wealth of information (a lot from people far more knowledgeable than me) that exists on the forum. Use the search function putting the key words into the advanced search and clicking on the 348/355 option.
You will see that statistically speaking, there is more likely to be a fault in the some of the components rather than an overheating problem - BUT THAT'S ONLY STASTICS. The system is there for a reason and you have to assume in the first instance that it's doing it's job and avoiding a catastrophic event. I would suggest (and this is where I can get shot down) that you should start by looking at the CAT ecu's; your car is 14 years old and these electronic components are known to fail.
Good luck Chris!

 

The cat ecu, or a thermocouple going bad.

You said you have a '95, so you should have the Motronic 2.7 main ecu units. Meaning that you should have two slow down lights. One for the 1/4 bank, and one for the 5/8 bank of cylinders. If so, you can swap the cat ecu's from side to side to see if the problem jumps sides, illuminating the slow down light for the other bank. If it doesn't then swap the cat ecu's back to their original positions, then swap the thermocouples from side to side to see if one of them is the problem.

As has been said, run a search of the archives as this topic has been covered many times.

 

Not hard at all.

When I had them in my 348 I could have them out in minutes. Unplug it, unscrew two 10mm nuts, and it's out.