WTF with the speedo

My speedometer on my 97 355 acted up one day too. It fluttered and then completely went dead. Strange thing was, my exhaust bypass valve started opening up at lower RPMs than it normally does, but only in 2nd gear. I then got a check engine light.

The next time I drove the car, the speedometer worked fine, but the check engine light did not go out. We pulled the codes and got "slow 02 sensor" for both banks. We cleared the codes and all was fine.

So is part of the metric for opening and closing the exhaust by-pass valve the speed of the car?

 

You know what?

Before you replace anything remove the instrument pod and check the connections on the back of the speedometer. The pod is really easy to remove. All you have to do is take out the 2 screws on the lower corners of the pod, get a firm grip on the sides of the pod and lift it straight up. You may want to lower the steering column all the way down to give you a bit more room for removing the pod. If you have the screws out and the pod doesn't come off, don't worry. The only thing holding it down is those two screws. So you may want to give it the ol' Fonz "tap" on the side to bust loose the rubber seal on the back side.

So pull the pod, and check the connection on the back of the speedo.

As for your light going out. Just because it went out doesn't mean that the problem went away. The ecu still holds the code/s. You have 50 starts of the car (at least on 348 ecu's anyway) then the ecu will erase the codes, or if power gets cut to the ecu's.
PULL THE CODES.

 

No, the Bosch Motronic controls the bypass valve. Not sure of what parameters it uses, but one mentioned in the workshop manual is exhaust temperature. If the car is not fully warm, then the valve will not open, or open at higher rpm than normal.

I would not recommend clearing check engine light codes without correcting the problem. It takes at least two 30 minute drive cycles with the problem to cause the CE light to trip, so it is likely your CE light will return again if you drive your car more extensively. And O2 sensors are inexpensive (for a Ferrari part) and easy to replace. As your car is 11 years old, it would be prudent to just go ahead and replace both precat O2 sensors. I had one fail on the right side a couple years ago, and should have replaced them both, as the left side failed a year later. Your car as the Bosch 5.2 Motronic, so for the pre cat the Bosch part number is 13819; you can search online for them, only $130 from Rockauto. Also check with Ricambi America, one of our sponsors.

You generally don't have to replace the post cat O2 sensors unless you get a specific code that they are bad. But if you do, the Bosch part number is 13820.

As far as the speedo....the sender bolted on top of the transaxle is failing. A common problem. It will either continue to by intermittent for a while, or just outright fail. Once it does, don't be surprised it will cause a suspension light to come on, as the Bilstein suspension ECU gets a signal from the speedo sender as well, and no signal will cause a fault code and the light to illuminate. Been there, done that. New speedo sender and the light will go out, no resetting of anything required. Easy change out, and Ricambi has the sender, around $130 or so.

Not to worry, these cars are getting old, so stuff needs replacing now days...

 

Thanks for the info. I will make getting the new o2 sensors part of my spring cleaning. I already bought the speed sender from Ricambi. I just have to install it.

The local Ferrari dealer (Algar) offers a oil change, brake fluid change/check the codes service. Would any nascent OBDII issues show up on their equipment? (i.e. there is a problem, just no check engine light...yet)

 

Yes, but any OBDII code reader would show them as well, but they may not really be relevant, so don't put a lot of trust in the codes stored that did not trip the CE light. BTW, any OBDII code reader can read your codes through your OBDII port, IF you have had the recall update performed. Check with your dealer (give them you vin) and see. It is a 15 minute fix, to correct the wiring to the plug so you can use a generic OBDII reader (against federal law, Ferrari originally wired the OBDII port so only their SD2 would work). Just remember, the generic reader will only show the basic emission codes, the Ferrari SD2/SD3 reads a whole lot more stuff. But no worry it is sufficient for fixing a majority of things.