355 Exhaust valve stuck, now Slow Down light - on a road trip, can I keep driving?

There should be no bad effects (other than noise.. and the Swiss Police ) if the valve is permanently open. I assume there is only one valve in the kit (?)

Does the light flash as soon as you start the car or only when the car is warmed up? I just want to make sure that nothing else is causing the issue.

Is there anything obvious? Loose vacuum pipe? Flat battery in the remote? Loose ground wire on the receiver?

 

I'm guessing you don't have a code reader.

These SD issues are always baffling. Some folks swear that the car works in a particular way, but other folks experience different things.

Can you simply bypass the remote to see if the symptoms change? Apart from the earth wire, the system seems to be "plug and play".

https://cdn.capristoexhaust.com/wp-content/uploads/sites/3/FB-Kit-Bedienungsanleitung-2016-A5-NeueFB-web-1.pdf

 

The slow down light is activated by a temperature probe in the exhaust system just after each catalytic converter.

If the probe detects an over temperature it will trigger the dash light. There are a multitude of reasons that can result in a SDL. I have read on here a few people that have experienced it after wiring their bypass valve open (while others have not had any such problems). If the bypass valve was stuck for some reason, that *could* have been the reason.

I would say drive on and see how it goes, but bear in mind that the weather is warmer than normal around here, and high ambient temp. is one of the things that bothers my 355, especially in traffic.

Not sure where you are in Switzerland, but where I am (Vevey/Lausanne area) it was quite warm last weekend (low 30C’s), and if you’re going south be ready for extreme heat. Last week I was down in Modena/Bologna for business and it was over 40C, this week the forecast is not quite as high, but still well into the 30s, so bear that in mind as a factor.

I hope you have no further issues, and a wonderful, memorable honeymoon.

 

If the bypass valve is stuck open, you will get an SDL because the engine ECU is expecting the thermocouple (temperature probe) to report certain temps at certain RPM's. With the bypass valve always open, the temp/RPM relationship is different -- in theory, the thermocouple is reporting high heat at RPM's when the bypass valve should be closed and therefore exposed to little heat -- and so the ECU thinks something is wrong and trips the SDL. (At least this is how I understand the relationship between bypass valve and SDL.)

The important thing is that the main cats aren't actually overheating. That is what the system is designed to prevent -- say, a stuck open injector or dead plugs that result in excess fuel dumped into the exhaust and burned in one of the cats, causing engine/exhaust damage or even a fire. Usually if something like this is happening, you will know because the car is running poorly.

 

At least it should be easy to diagnose when you get home.

Remove the remote system (to prove it isn't the remote intermittently failing).
Look for codes (don't reset the battery to get rid of codes)
Figure out if your car has 3 Thermocouple ECUs (I believe some cars feed thermocouple data directly to the ECU).
If the wires are long enough, you may be able to swap all the connectors on the Thermocouple ECUs to see if the codes change.
Check vacuum supply. Sometimes the check (one way) valves in the system fail and you don't get enough vacuum (on Capristo systems) to close the valve. There was a recent message thread on this.
https://www.ferrarichat.com/forum/posts/149140374/

As you say, it does seem to be the bypass system failing and not the main cats.

 

While you may think the car is safe to drive with the bypass valve open and a flashing SDL, the ECU will not think so. Your continued driving with the SDL flashing will eventually force the car to go solid SDL and then to shut off the ignition.

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Not necessarily, I think. If the SDL is triggered by the "wrong" position of the valve, and not by high temperature of any of the CATs, the ECU may not go into solid SDL and shut down any bank (there is no reason for that). I do not know this for sure, just trying to apply some logic.

 

I once had a flashing SDL triggered by the bypass valve, and I drove it for weeks like that, and the ECU never shut anything down.

It's an interesting question -- can a bypass SDL cause an engine shutdown? I don't know the answer. I would think not. In stock configuration, if the bypass fails, it's closed, so the exhaust runs through the main cats. Those already have temp probes that can shut down a bank or the entire engine. So why would the bypass SDL need to do that?

 

So, in your case, was the SDL triggered because the valve was stuck closed, not because of high temperatures after the bypass valve?

Mark, does your car have cats in the bypass system? USA/Canada/Czech Republic?/Switzerland & Japan have cats in the OEM system.

https://www.eurospares.co.uk/Ferrari/355/355_(5.2_Motronic)/PartDiagrams/016/Exhaust_System

Further to what has been said, is there a point having shutdown for high temperatures in the bypass system if it's not protecting these supplementary cats?

We have to ask if the light logic has multiple triggers and/or if these triggers vary from country to country. The ECU has 12 variations.