308 GTS QV - Engine misfiring (or similar!)

Crank position sensor?

Can you indicate what the Ferrari specialist has checked and ruled out?

 

This is a strong clue that the coil primary for the "bad" bank is not firing (and it's the bank whose Digiplex ECU is supplying the tach signal). Top suspects = TDC crank sensor for that bank as moysiuan suggested, or Digiplex ECU for that bank, or coil/coil primary connections for that bank. Intermittent Gremlins are the worst. If the problem can get more consistent you can swap components and see if the problem moves to the other bank, or not, to find the bad player.

 

I had exactly a similar problem last year. RPM dropped to zero, lost a bank.....then it would come back. Ultimately, while trying to isolate which bank was the problem, I unplugged the digiplex units and after plugging them back in the problem disappeared. Just a bad contact. So that's where I would start.

 

Looks like they did their best to deal with a problem they could not recreate. The crank sensors are just magnets, and the degrade with time and heat. The heat once warmed up might be the cause. They magnets dont necessarily fail in a binary way, so can present intermittent issues. I would replace, even if not the problem it is reasonable preventive maintenance from age and not big a job to get done.

 

It could be the connector connecting the sensor to ecu wiring too (as was on mine).

 

I had exact same problem a while ago. Turned out to be electrical connectors right beside drivers rear wheel liner. Did you have you wheel liner out recently? Try cleaning them up and reconnecting. Not saying it will be your fix, but at least you can rule it out if it doesn’t work.

 

On the QVs there are 2x2 wires departing from that plug, one to the ecu and one to the diagnostics plug. In my case, the one to the diagnostics plug was fine so when I tested from the "outside" via the diagnostics plug, it all checked out. But its twin wire to the ecu had broken so there was no signal at the ECU.

 

A cold start injector could simply leak - even when not powered. Not saying it is the issue here but the only way to rule it out would be to remove it from the car, place it into a container to catch potential fuel, blank of the plenum hole, start the engine and run it to see it it leaks fuel into the container.

Unplugging it is a test for the thermo-time switch controlling it, not a leakage test of the injector.