355 5.2 OBD codes: 0422,0432,0153,1121

Agreed but if you have exhaust leaks and the sensors pre and post cat are functioning you are going to get codes due to them sensing a lean mixture.

 

Pretty sure I mentioned something about sealer?

 

Sealer on every joint. It just offers a a sealed joint. Rear to front/front back it won't

 

I don't know what sealant you have but nothing on a Ferrari exhaust should require sealant.

 

Sorry John but I disagree with you on this one. I don't know of to many cars that don't develop exhaust leaks without some sort of sealer. Maybe they didn't need it new but after its been assembled and disassembled there are going to be leaks. Age has a bit to do with it also. Anyways that's just one opinion I'm sure there are pro's and con's to this argument.

 

That's fine. The system was design for dry fitting. Anyone can do as they please. The OPs problem is due to having test pipes and trying to fool the ECU that cats are in place. In his case it is possible that a small leak up stream could negate the effect of the mini cat extensions for the rear O2 sensors. If it were my car I'd put high flow cat on a ditch the test pipes which would most likely solve the problem.

 

Previous posts of the OP state that after a smoke test multiple leaks were detected. These leaks are not going to help the ecu read what's happening in the catalyst system. If he can eliminate the leaks this will assist in the finding why the car is producing CEL. All I'm suggesting is help in fixing the leaks then he can move his post cat sensors in or out to find a happy/medium voltage.

 

Agreed Paul, fix the leaks, but nothing up stream of the cats (or test pipes) should require sealant. They are all compression donuts. If they leak it's the way they were assembled or perhaps the flares on the test pipes aren't correct.

 

Mine sucked smoke in/out at the thermocouple compression fitting. Fixed the leak no more CEL. These cars are made to test us.

 

The exhaust gas does not have positive pressure all the time but it has brief periods during the engine cycle when it is under certain vacuum. In properly designed exhaust system, this vacuum is used to help scavenging of the exhaust gasses from the cylinders. This phenomenon is also used on the 348 for air "injection" which is actually suction of external air by the exhaust, controlled by the check valves which are closed during the exhaust pressure phase and they open during the suction (vacuum) phase to let fresh air into the exhaust. This is a typical graph of the pressure and vacuum phases of an engine:
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Interesting, thanks, Miro. Does the graph show the sum of the pressures (i.e. at the confluence of the 4 exhaust streams or just the pressure at the cylinder exhaust port?). I'm wondering how much the cat would damp the pronounced pressure fluctuations (assuming Carmellini didn't have test pipes).

Ah, I forgot the 348 doesn't have a secondary air pump like the 355. I can't recall if the secondary air system was checked for leaks. Even if the pump were to be turned off by the ECU, if there was a secondary air leak (on the upstream side of the check valves) the cylinder vacuum might be drawing unwanted air into the system.

 

I believe that the graph shows pressure/vacuum ("+/-") at one individual cylinder and its exhaust port / manifold branch. When tuned exhausts are designed, care is taken that when these pulses are summed (from different cylinders) downstream, they don't clash "+" from one with "+" from another cylinder but the pulses are summed like train carriages pulling each other down the exhaust pipe. After summing, there are obviously still some suction phases as Paul reported that he had smoke in/out at the Thermocouple compression fitting.

 

Hense my statement regarding total exhaust be leak free. From what has been explained to me through this thread the ecu has a small window of voltage operation window without eliminating the CEL. One thing to help code issues is to eliminate exhaust leaks. While at low engine speeds the exhaust pulses maybe evident but as eng speed increases the pulses of blowing/sucking maybe harder to evaluate.

 

You can report which one worked by doing one thing at a time.
You will know for sure it's fixed after a few good drives. Pays to check for pending codes with the scanner along with watching the sensors live as previously mentioned.