It is believed that the rattling/knocking produced during cranking by the (thin or no grease) flywheel causes the knock sensors to produce erratic signals to the ECU-s and affect ignition timing. It either causes the ignition to be retarded significantly or to be completely interrupted. This effect may be reduced (as a temporary solution) by starting the engine with the clutch depressed and the transmission in gear.
Seems odd that the knock sensors would be so sensitive to that because they generally work on detonation! But you wouldn't know what the bloody hell Ferrari were thinking either. Seems a fair analysis though. Cheers for sharing that. I suppose disconnected knock sensors for a test certainly wouldn't hurt if you had cold start issues.
It is not the knock sensors that cause the problem, but the engine RPM and phase sensors that cause the issue. The rattling flywheel causes erratic signals from theses sensors which will cause faults to be stored and hard starting issues. If the flywheel rattles on shut-down and the car starts better when the clutch pedal is depressed, the the flywheel/grease is typically the cause.
The knock sensors are quite sensitive (they can easily be damaged if dropped). They do not directly recognise detonation in the combustion chambers but sense the mechanical waves (vibration) in the engine block created by the detonation. The knocking/rattling of the flywheel easily transmits through the engine and the knock sensors can pick it up and understand it as detonation.
In that case, what I've read was incorrect. It could then be the cam position sensor (the hall effect transistor) but these are normally not affected by shock or vibration. The only remaining thing is the crank position sensors.
I'm not disagreeing they are valid points! I just cant get my head around the fact that the Crank ref is just a magnetic pick up looking for a missing tooth? at the other end of the engine. It would have to be extremely sensitive to be changing a rising or a falling trigger that would up set the starting of the engine. Just my thoughts
For some reason, the unbalanced system does not spin right up to speed with the starter engaged and ignition is cut off if the RPM does not meet a certain number. My 348 did that for the longest time until I repacked the grease.
This would certainly apply to a low battery not cranking fast enough also. If the sensor needs a certain amount of cranking revolution or as you say cancels or won't give a timing signal to fire up the engine. Possibly just a little bit TO much sensitivity on Ferraris part
yes, the computer is looking for 30 rpm to turn the fuel pumps on. If the car shuts down it shuts off the fuel as a safety feature. It takes the rpm reading off the crank sensor
I'm guessing the engine speed is determined by the difference between the signals at the crank sensors, of which there are two at 90deg from each other. Lack of grease in the clutch will cause irregular signals between the two that the brain is unable to interpret. I wonder.... is this a problem on 355 5.2 as well. If not, maybe that's why..
