Consistent C. Stradale Misfire: running out of ideas

How does the compression and leak down look?
I had a similar problem with a Euro 360 a while back, with nearly identical codes. A Picoscope observation of the MAFs from cold revealed that one MAF behaved oddly only for the first few minutes of operation. Have you measured exhaust emissions at the sample ports? Injectors: have you had then tested?

Just a few thoughts...

 

Check the back EMF from the affected cyls.
I've struck it on 360's before. You may need a blocking diode across the injector. What are the short and long term fuel trims like?

 

I'm reaching out on a limb here, but a relatives 1996 Mercedes had a problem with engine misfire and stalling. It was diagnosed with a bad engine harness. The repair shop gave her an estimate that was overly expensive for her and the car. I took a look at it and sure enough the harness insulation was falling apart. I jumped online and found many MB's doing the same thing. The people online were referring to the harnesses as "Biodegradable Harnesses". I found there were three harnesses that were desinagrating, engine, transmission, and low voltage ignition. All three were pretty advanced and the worst was the low voltage ignition harness and probably the one that was causing the misfire and stalling the engine. The harness outer sleeve was fine, but each of the four conductors had 25% of the vinyl gone with bare wires also in poor state intermittently touching each other.

I ordered the three and changed them out. It ran fine for a year and now it has an engine power problem. I believe the harness on the induction throttle body has gone the same as the others. All the time this car has never thrown a CEL and only a few P0300 and P0304 which are general misfire and cylinder #4 respectively.

I really hope this is not true with your car but both the MB and Ferrari use some of the same suppliers.

Again out on the limb, but you may trace the low voltage harness with and ohm meter while juggling the harness.

 

Another odd one to throw out there, my M3 yrs ago developed an odd hard to track missfire. Reason, sticking lifter. The 360 has hydrolic lifters and if they are sticking it'll cause odd issues. The loud metal on metal sound could have been a collapsed or sticking lifter causing valve train noise and possible piston to valve contact. A good vacuum gauge to monitor the needle movement would help a lot it diagnosing what is going on. I honestly don't recall if the leonardo has real time graphing at the moment but if it does that would be very very helpful.

 

I had a similar problem over a year ago on my '03 360 Spider. Checked intake gaskets, coils, spark plugs, injectors, MAFs, O2 sensors, fuel pressures, and all are fine. Next on the list was loose vacuum hoses. I smoked the engine and I found a few. Still misfired and banks running lean CEL codes. I scoped the bank 1 CKS and found it to be OK, but the problem still persisted. On a whim, I replaced the bank 1 CKS and the misfirings on bank 1 disappeared but still occasional misfires on bank 2. I then decided to replace the bank 2 CKS and that fixed it for good. What a chase! Apparently, due to old age both CKS were malfunctioning intermittently. The CKS are cheap, I got them for about $75 USD each.

 

Yes, it's the crankshaft position sensor. There is a thin metal shim underneath the sensor. Pull out the sensor slowly and don't lose the shim. The shim is there to properly adjust the air gap between the sensor tip to the teeth of the crankshaft reluctor ring. Don't drop the sensor because there is a magnet inside and it might crack due to a sudden shock. After replacing the sensor, power off/on the master switch to reset the fuel trims. Start car and let the ECUs go through the relearn cycle. It's a 10 minutes R/R for each side.

Because of old age, I highly recommend replacing them because CKS faults doesn't necessarily set the CEL. As proven in my case, it can operate intermittently without a hard fault and you'll be spending many hours chasing the cause of the problems. And finally, if one of them dies while you're on the road, you'll be stuck. The engine won't start unless the CKS sends the right signals to the ECUs.
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While this is probably not the cause of your problem, but whoever did the last cam-belt replacement did not set the cam timing perfectly. The exhaust cam timing should be 657 on both banks and not vary by more than one degree between banks. It is 656.8 on the left bank, but only 653.6 on the right bank. The cam timing may be off on the intake cams as well, but you cannot check them electronically, only with a dial indicator.

 

intake manifold gaskets ... Happens all the time the old paper ones crumble and leak

 

Items I would look at:
Freeze frame data with the errors. This will at least give you an RPM range and load the concern is occurring at.
Cam timing is concerning. 654 is preferred not 657 and should be within 1 degree. if this concern did not occur immediately after a service it likely isn't the cause but it should be corrected.
I would strongly suspect you have leaking lower intake gaskets.
The clanking you described concerns me. I have seen two things cause this. Broken outer valve spring on the intake valve. It may even idle great but under load it will backfire into the intake and cause random pretty consistent miss fire on one cylinder and random miss fires on others usually on the same bank or companion cylinders. Compression and leak down may look normal at cranking speeds.
The other concern would be a failing catalyst being ingested in to the engine. This will cause all kinds of random misfires and can occur on both banks and may cause the noise.

 

That temperature sensitive is not a valve spring. Poor injector spray pattern, dirty injectors will cause that. Euro fuel and the Euro software in that car is a lot different then US and may cause cold start issues. I have seen secondary cats make it to the engine but if it is that temp related its obviously not mechanical.
How old is the fuel and does it have alcohol in it? I would have the injectors flow tested and cleaned.

 

Leave the car sitting for a few days and measure the fuel pressure at the rail you have the consistent misfires on. I'll wager that when the ignition is turned on the fuel pressure will climb and then fall immediately. The full spec for the pressure test is in the workshop manual.

 

@24000rpm : did you find out anything new? Thanks for any update.

 

Few years ago I had a car with similar problem in my workshop. It was 1.2 HTP Skoda Fabia, showing misfires on cylinder 2 and 3 when the engine warmed up. It was caused by the injector on cyl.1 that sprayed bigger amount of fuel than expected, causing ECU to lean the mixture till the other two cylinders started to misfire due to the fuel starvation...