Slow down Cylinders 1-8

This is a very comon problem on 348's. The reason the light comes on, is to warn you that the cat is overheating on that bank of cylinders. If you continue to drive the car the ecu will shut down that bank, to prevent damage to the catalytic converter. The light will stay on so long as the ecu is getting a reading that the cat is hot. Once the cat cools down then the light will go off, but the ecu will have a code stored in it, indicating that you had the problem. It usually is one of the following:

1) Your cat has truely overheated and the ecu has warned you of this. Meaning you need new cats.

2) Your exhuast ecu has gone out, giving a false reading to the engine management ecu. Meaning you need a new cat ecu.

3) You have a bad thermocoupler, and it is sending a wrong signal to the exhuast ecu. Meaning you need a new thermocoupler.

You can test to see if it's a bad cat ecu by swapping the cat ecu's from one side to the other. If the problem pops up on the other side then you know that the cat ecu is bad.

If you get the problem again on the same side then it would be safe to say the your catalytic converter has had it. That or you could have a bad thermocoupler.

p.s. don't you mean "slow down 1/6"? As far as I know Ferrari hasn't made a 16 cylinder engine yet. LOL.

 

You have the only 16 cylinder Testarossa ever build, COOL!!!

Seriously tho, it is probably the O2 sensors.

 

The O2 sensors would throw a check engine light, not a slow down light.

 

No check engine lights on a TR (thank goodness ).

The only way an O2 sensor can cause the exhaust warning lights to come on is if the (bad) signal from the O2 sensor is causing the injection system to (wrongly) add excess fuel which gets ignited in the cat (i.e., a true overheating situation) -- ernie's #1. If after extended driving the warning light comes on, stop and have a quick visual look -- a truly overheated cat would be "glowing" a bit (and probably "smoking" a bit as nearby components get overheated from the radiant heat transfer.)

If your cat isn't glowing red-hot when the light comes "on" or the warning light is not doing it's self-test reliably and/or it comes on at wacko times (like immediately after cold start-up, or with key "on" but engine not running) then probably per ernie's #2 -- swap the warning light ECU's and see if the "problem" moves to the other bank. Can you explain "Actually defaults when key power to car is switched without starting then continues" more clearly?

The only reason IMO to replace a cat (on a TR) is if the internals have melted/broken and are impeding the exhaust flow (i.e., cats themselves don't directly cause this "overheating" problem).

 

Can someone explain why a bad CAT will overheat? how does it wear out to make it overheat?

 

you did not mention this as a symptom, but i will throw my 2 cts in....i had this light go on once after a rainstorm and the engine coughed and spluttered and was in fact only running on 6 cylinders. i returned to the dealer and we discovered that water had seeped in through a bad seal on distributor and shorted that bank of plugs....

this is probably not the cause for your light going on, but while we were on the subject.....