456M won't start / firing out of time

Pages C6-C9 of the WSM clearly identify how the engine determines its position within the firing cycle. In essence, the are two crank sensors, one for each bank. There are "missing teeth" on the trigger wheel that tell the ECUs that the engine is at TDC. However, without the trigger from the cam sensor on the 1-6 bank, the engine has no idea if it's on the TDC compression or exhaust stroke. Hence, the first order of business would be to be a scope on the cam phase sensor (waveform shown in the WSM).

Secondly: The SD-2 will indeed reads faults without the engine running. Turn the key on, disable the alarm...and faults are easily read.

 

220 lbs of compression?

Awfully high for a 456.

All internal combustion engines require the same 3 things to run

Compression
Ignition
Fuel


Based on your symptoms, your obviously flawed compression number, it's fundamental importance to the combustion process and the fact that problems/failures often occur during the starting process I'd be getting some covers off and confirming cam timing. I have seen more belt drive (and even chain drive) failures at startup than any other running mode. An electronic component failure at startup on the other hand is considerably more rare.

If that is a real compression number I'd also want to have all the plugs out to see why before something really expensive gets broken or damaged.

 

Seems flawed or no diagnostic pathway.

 

The only thing that can alter a compression reading is cam timing, unless there is somthing else seriously wrong. As brian said, 220 is way high. Did you test both banks?

 

Upload the video on youtube and just post the link.

Get those cam belt covers off and take a look!

 

Great work, you did remove the covers - it seems that the belts were changed, but by the sound of it I would say very high probability that the car is out of timing.

You need to change the timing marks.

 

Not true

 

One time on a friend of mine 456m,the aluminium crown around the engine clutch plate was disasembled a little because of a overheating when bad shifting(ex two stroke moto racer!)
So the teeth of this crown were not at the right place for firing ....
Flat bed aso...
The diagnosis happened when changing the clutch....

 

So an overheated clutch caused the timing gear to shift? Intriguing. Did he have the same symptoms? The car in question here did not have a clutch overheat as far as we can tell by the information we have. That does not mean a shifted timing gear is not a possibility.
In fact the recent diagnostics have made that more likely. It would account for the issue occurring on both banks, as it is one of the few shared items left and right. I would suspect firing timing to be determined by the crank gear and not the cam sensor, as it is more precise and more relevant.

 

Check the cam timing - so you can rule it out.

Also take a look into the cylinders.

 

The sensors of the crankshaft top dead center are from the teethed crown on the engine flywheel.
this crown is in aluminium ..and nobody knows if maybe on just one off slippering clutching shift this crown had overheated and change a little of its position on the steel flywheel...
Bad top dead point ...
I kept my friend one on a shelf..
Heavy...

 

First time I have heard of this happening, interesting,? I interperate this as alluminium center with steel ring?

 

No excuse me it is a steel flywheel and a crown around with a different steel .this crown is not welded !. If a overheating happens this can move a little..

 

Good to know.
Note to self pin ring gear

 

I Spoke to my Ferrari tech today and he has seen two instance of the ring on the flywheel moving and the engines not running correctly, one on a 550 and another on a 456

 

Graeme, was that shift in timing on those cars in retardation or advance? My theory that retardation is most likely does not mean a shift to advance is not possible, that's what theories are for .
Assuming the fault really occurs on both banks at the same time: there are only a few things shared, it seems this is becoming the best lead for the owner now to pursue.
Next to this, I would still check for "clean" power lines to the computers as well, it has not been indicated that has been checked. It is one of the few other items shared left and right.

I would start by getting a book or similar documentation on the Bosch motronic, so it is known what the exact position of the 'missing tooth' on the crank gear has to be relative to TDC. This can easily be checked from the holes for the crank sensors and inspection hole, all at the bottom of the bellhousing.

 

Still does not explain why your compression readings are so high - should not be affected by ignition timing.