Slown down light but no check engine light coming on

Slow down light means only one thing, that the thermocouple is measuring to high a temperature on one of your cats. The fact that you say its glowing orange confirms this! The slow down light will flash over a preset temperature, when it reaches the next setpoint (not sure of the temps) the light goes solid and it will shutdown that bank of cylinders to prevent fire, as you have found. Id get it in and get it hooked up to SD2 and see what is causing your CEL. The slowdown system sounds like its doing its job just fine.
Dont risk damage/fire, get it checked out, im guessing your cat has collapsed.

 

To my knowledge, which is imperfect but nonetheless substantial when it comes to the 348/355 Motronic systems, there would be no reason for the Check Engine lights to come on simply because of overheating catalytic converters.

The thermocouple is a sensor that sends a signal to the thermocouple control module (a.k.a. thermocuple ECU, a.k.a. cat ECU); and if the thermocouple detects high temperature in the catalyst, then it will communicate to the ECU, which will in turn communicate to you by throwing on the Slow-Down light. It doesn't send a Check Engine light.

Now, if an underlying problem caused the catalysts to melt -- like the engine running rich -- then you might see a Check Engine light. In other words, if a problem area covered by a sensor that has the ability to throw a Check Engine light is indeed the cause of your melted catalyst, the Check Engine light should have come on. If, however, your catalysts are simply old and no good (which is very possible considering that all Ferarri catalysts installed on mid-engine Ferraris between 1989 and 1999 are crapola) and simpyl failed on their own, then only the Slow-Down lights would come into play.

I have just decoded your error codes, and it looks like your lambda (oxygen) regulation was off, so there could be your problem because a rich engine will fry a catalyst or both. As far as I can hypothesize, it seems that the Motronic did not throw on the Check Engine light again for two possible reasons: 1), the lambda regulation during the time interval in question was normal; or 2), the code was stored in memory, so the Motronic decided that it didn't need to tell you again. Since you did not indicate that you cleared the ECU history (I don't think simply shutting the battery off will do that), I would venture to say #2 is the reason.

Now I realize that the sheet I have attached does contain Check Engine light error codes for catalyst temperatures being too high, but I question the validity of that information because i myself have fried a catalyst without ever seeing a Check Engine light (unfortunately, my thermocouple ECUs were disconnected at the time unbeknownst to me -- a big no-no -- so I didn't have the fortune of ever seeing a Slow-Down lamp). I only wish that I had seen a Check Engine light. So I am using my own experience as a challenge to the textbook -- and we know that Ferrari textbooks are often wrong -- but I realize that I certainly may be incorrect.

Let's let the experts chime in.
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On another note --

You need to do two things: first, test out your catalysts to see if either one has been killed; second, test your engine and make sure it is running properly. You need to find out why your catalyst was overheating.

The way to do this is to conduct an exhaust gas analysis using a 4-gas analyzer. Test the gases BEFORE the catalysts -- there is a port on the exhaust manifolds for this purpose. The reason for this is that the engine should run fine on its own WITHOUT the oxygen sensors. Your technician should know what parameters should be normal for a pre-catalyst analysis.

The engine ought to be running fine on its own (without the oxygen sensors) -- so if it doesn't pass that first test, then you know where your problem is.

Then test the gases AFTER the catalysts -- that is, test the gases from the muffler pipes. The numbers also should be within specific paramters -- you will know at this stage if the catalysts are doing their job properly.

But if the first set of numbers BEFORE the catalysts are outside of the normal parameters, don't bother with the post-catalysts test. The oxygen sensors and the catalysts are not supposed to correct an engine that is not running properly. The oxygen sensors are meant only to make minor fluctuations in fuel mixture: they are not supposed to correct an underlying problem -- and they won't.

You have a serious issue on your hands, and you must not drive the car. A glowing catalyst is tantamount to having the kitchen set on fire. A kitchen fire can be extinguished without damaging the rest of the house; but unless you want to see the whole house burn to the ground, I would recommend having an expert help you.

 

I may be real dumbo here... but...

CELs have been known to be disconnected... Say yours burned out/ were disconnected how would you know?

If your CAT is glowing, you're dumping too much fuel in there - eg. consistently too rich a mixture. The ECU will stop using he Oxygen sensor values when they deviate more than 20% from the expected values (.7v) and go to open loop. In open loop, the mixture is set by the CO screw on your Air mass sensors, which should be somewhere around 383 ohms (measuring between pin 6 and either 1 or 2 with an ohm meter).

The Cat ECU's flash the "Slow down X-Y" at 700 degrees C, then light permanently at 750 degrees C. On a Motronic 2.5 system the Exhaust ECU is not wired into the Motronic ECU and so will not shut anything down (does it on the M 2.7 cars?).

So if you have a Motronic 2.5 car with burned out / disconnected CELs and you're burning out a cat either through overly rich mixture or otherwise, you won't see a CEL. if the CELs are working, then if the cat is heating up due to a blockage then you still will not see a CEL...

You wrote that you have replaced the O2 Sensors - check the connections again. Secondly measure the MAF CO value and set it to 383 ohm (lower value = lean, higher = rich) so that if the O2 does malfunction then you will not burn out the cats, and CHECK YOUR CEL bulbs!!!

P.S. if you have a Motronic 2.5 (1 throttle position sensor only on 5-8 bank) can you tell me which ECU pins connect to the CELs in the US cars?

Good luck,

Marco

 

Please let us know what his diagnosis is.

 

Brian Crall will know exactly what to do. He is the teacher.

 

You still should have an analysis done on your exhaust gases before the catalysts -- that is, if you are a believer of the philosophy of erring on the side of caution.