Hey Guys, Mostly for my own learning now, but I am trying to understand a lot more about O2 Sensors, Catalytic Converters, their interactions with the operation of the car, and more. I have searched this forum for a couple of hours and read about a dozen relevant threads on here, and I still have some questions I am hoping you guys can help with here. I am not currently trying to make a change here, but I am thinking about making a change in exhaust system and wanted to better understand all I was reading here - particularly the consequences of a cat. delete pipe solution. 1) The Rear O2 Sensors (after the Catalytic Converter) . . . does their output actually affect the operation or A/F of the car, or is it primarily for reporting a fault or unexpected condition? What I am getting at . . . is it if it reports something like "Aged O2 Sensor," "Worn Catalytic Converter," or something that insinuates that the catalytic converter is not working . . . does it affect the operation of the car by feeding back data to the ECU, or is it primarily to let you know there is a fault? 2) What is an O2 Extender? Does it result in reducing the voltage output of the O2 sensor, thus telling the computer all is well? 3) What type of problems can this cause (outside of, of course, violating laws and having a vehicle that isn't suitable for resale until this is all corrected)? 4) With a Cat. Delete Pipe solution on a 550, would you just need to do this on the Rear O2 sensors (post. cat.)? Hypothetically, would a Ferrari 550 with a cat. delete pipe solution run well or have any adverse side effects?
Viv, you may not get a strong response here, due to the sensitive nature of the topic, but I can tell you what I know about rear O2 sensors. In our OBDI cars, the rear O2 sensors were used only as a check to ensure the front ones and the Cats were working, but with the progression to OBDII, some car/ECU manufacturers decided to use the the rear O2 sensors to adjust the fuel trims to account for aging of the front sensors and the cats themselves. This is called Fore/Aft Oxygen Sensor Control, and Ferrari (or Bosch) evidently adopted it according to the WSM for our cars (see point "b" on page C14 of the WSM). I don't know under what conditions the FAOSC fuel trim control is implemented in our Motronic 5.2 ECU's, but based on other cars/ECU's, I would think it's under steady state, cruise type conditions, where the ECU's can get fairly stable readings from the aft sensors. The extenders can be a mixed bag. Some claim good success, some not so good. If I were to attempt to use these things, I would watch my STFT and LTFT's closely for signs of unwarranted richening or leaning of the mixtures. If I were doing it with test pipes, then for sure I would include additional bungs in the test pipes for wide band sensors, and I'd monitor the AFR's.
Good question.. I can not tell you much about the O2 sensors. But I can tell you that the engine is made and calibrated to operate with a catalytic converter. When I bought my car, it had cat delete pipes. It had a "slow down" message in the dashboard. When I put on the cats, the message dissappeared instantly and the engine had much more bottom end torque, and got better milage and ran smoother. The cats also make sound so the sound picture changed. It also "filter" the sound imperfections, so the car sounds much more civilized. You can of course play with sports cats or delete pipes, but I just don't see the point as these cars are pretty powerful anyway. Good luck and post your results.
To be clear, I have no intention of purchasing cat. delete pipes or removing catalytic converters from my car (I just bought Ricambi Hyperflows a year ago). I do very much enjoy being able to get my State Inspection at any local Inspection Station without any trickery. So, I won't have any results to post . . . I genuinely was just trying to understand the system much better. I was reading a lot of threads about exhaust sounds, notes, arguments about straight pipes vs. X-Pipes, cats. and no cats., and more . . . and, it left me with a lot of questions I was hoping to get answered here. I figured someone would know and be able to help first hand.
Another related question . . . are standard off the shelf OBDII scanners able to read Check Engine Light codes on this car that may be caused by the Rear O2 Sensor? Or, does it require an SD2/Leonardo at a Service Facility?
Vivek- Nearly all the emissions related OBD II codes can be read by a generic OBD II scanner, by DOT/EPA edict. Ferrari got in trouble with the EPA because they tried to set up their OBD II connector so only SD tools could read the codes. They had to do a recall to fix the connector or face fines. Here is a list of the generic codes. OBD-II Check Engine Light Trouble Codes
I have deleted the secondary cats on my 575M and re-installed the EGT thermocouples into the same place on the cat delete pipes. I have had no CELs. The 4 primary cats have the Lambda sensors fore and aft of each one with none monitoring the secondary cats. What do the secondary cats do besides restrict the exhaust? Will it pass an emissions sniffer without them?
Willy- Pre-cat primary function is to clean the exhaust gasses before the main converters come up to temperature and thus lower emissions during the start phase. The precats in the headers come up to temperature much more quickly than the main cats further down the exhaust stream. In theory, if the car is fully warmed before an emissions test, which it normally always should be, removing the pre-cats will not affect an emissions test. Removal will, obviously, increase overall emissions. There is no feedback loop for the precats.
Taz if as you say the there "is no feedback loop for the pre-cats" why are the Lambda sensors placed either side of the pre-cats?
Willy- Sure looks like a feedback loop, does it not? Should have looked at the parts catalog drawing first.
Hi Taz, thanks. Will a generic scanner also be able to reset the Check Engine Light set by some codes? Or, will that somehow wreak havoc, also?
Vivek- The OBD II reader should be able to reset some CEL codes. Whether they stay off is another thing.
