348 Slow down lights, final truth

Thanks for the response Rob, I thought that there were probably more monitoring system failures than Cat overheat problems. If there were a higher no. of overheat problems(like your Honda experiance)more manufacturers would be using it. Regards, Vern

 

No.

If you have cats, then you may want to disable (or spoof the signal of) the one exhaust ECU wire that signals the A/F ECU to shut down a bank of cylinders. That at least leaves in tact the sensing and Slow Down light functions for safety.

If you don't have cats, then you may want to either connect the two xECU wires that go to the thermocouple to a "correct" resistance value, or, if the design is based on voltage, then you may want a small circuit that applies the correct voltage to those two wire.

 

No, it won't.

Engine management systems and other electronic systems such as stability control (a misnomer, should be stability assist) all have the same foundation of architecture: sensor(s), computer, actuator(s). If some component in not monitored by a sensor, then there is no way to take action during a malfunction.

For more information I highly recommend the Bosch Handbook available through Society of Automotive Engineers.

Best,
Rob

 

My 89 348tb had a melted Cat and evidence of a melted driver side tail light. It seems that the pressure regulator wasn't modulated by the vacuum input from the plenium. You could reset the motronic and as you drove the thing, the driver side change over a months time to the point where the motor would not idle. Reseting it once a month worked until I found the problem. On the 2.5 system, there is no interaction to the motronic from the thermocouples but the 2.7 does have a connection. The car also had a loose ground connection on the driver valve cover that would cause one bank to cut out. Wish my great diagnostic skills found the problem but actually, I was playing with something back there and a bolt rattled out from under the car. I made test pipes to reduce weight and thermal loading (left the thermocouples off and hooked up a Tubi......it sound like a F1 car! Yahoooo! YMMV

Jeff Pintler
89 348tb, 86 TR

 

Hi Jeff, You didn't say if your slow down light came on or not. I am assumming that it didn't or you would have found the problem sooner. Another example of the problems with this monitoring system. Hummm...They work when there is no problem and don't when there is. LOL Regards, Vern

PS Don't you love the sound of an unrestricted exhaust on a Ferrari?!!

 

Just a quick update on the slowdown warning for the 550. Spoke to my dealer today, apparently the resistance of the thermocouple probe is 800ohms cold, 350 hot.
Ferrarifixer has soldered in some 680ohm resistors and has advised the slow down light has now gone out, which did not happen with the thermocouple ECU inputs simply bridged. Only time will tell, but so far it looks good.

 

Thanks for the update. Now we know that Ferrari did indeed use the resistence method rather than the voltage method.

Thus, your resistance fix will work fine (for a car with no cats, at least).