355 Cam phase sensor malfunction

He already swapped out for a know good TCU and that is not the problem so … moving on

 

There is no signal coming out of the ECU for the ignition coil. The coil has +12V on its middle pin and the side pins are switched to ground by the ECU, alternating one and the other according to the firing order. You can possibly check whether the ECU is switching to ground if you unplug the connector from the coil and connect an LED diode as shown on the picture. The LED should blink when the engine is cranked (fuel pump relay taken out). You may be able to use a car bulb instead of the LED/Resistor but the bulbs are slow to light up and may not catch the brief pulses.

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How are you tapping into the signal? Needle into wire or checking at ECU connector backplug?

 

So one lead was on the ECU backplug pin 49 and you used a long extension wire to hook up the crocodile clip scope lead to get to the grounding stud in the engine bay? It would have been easier to hook up the crocodile clip to pin 6 on the ECU plug.

Well, there could always be wiring shorts to ground, taking the trigger volts away from the coil pack. When you do continuity checks on specific pairs of pins, it doesn't mean that the wires are not rubbing against the chassis at some point. The best way to check for shorts is by disconnecting the plugs at both ends (ECU and coilpack) and make sure that the outside wires on the 3 pin plug are not shorted to ground. Put one of your ohmmeter leads on pin 1 (or 3) and the other to an earth on the chassis or engine. Hopefully you get open circuit.

Does the Ferrari cam sensor respond to a special tooth on the cam or lack of teeth at a particular point on the cam? On other type of cars, I've heard these teeth can be damaged and the sensor can no longer pick up the signal (but then it's usually an improperly shimmed sensor which damages the teeth and/or the sensor and this would be easily noticed).

I'd say the most likely problem now would be a damaged ignition driver chip in the ECU. These are easily repaired (by ECU repair companies) on regular cars, but the Ferrari ECU has that immobiliser circuit. I tried to identify the chips in online pics, but not all the Bosch chips showed up in Google.

http://ferrariworkshop.com/content/4-motronic-5-2-ecu-modding-performance-1996-99-a.html

Off-topic, but the chip circled in yellow is the immobiliser chip.

 

Based on all the checks you have done, it appears to be the problem is in the ECU. Hopefully, the engine will be back to normal with the second ECU.

If the second ECU proves that the first one developed a fault, you can try to repair it (or have it repaired). The failure of one bank ignition could be simply due to a PC board solder that went "dry" or a failure of the ignition power transistors. You can try to trace the links of the ECU pins that are connected to the ignition coil side pins to determine which transistors control them. However, since the whole bank is not firing, it would mean that both transistors (for one and for the other side pins of the coil) have failed simultaneously which is unlikely. The pictures below shows an example of a 5.2 ECU (a 4 cylinder car) and the ignition transistors and links inside it.

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Did the oscilloscope work on the left bank?

 

Just reading the Workshop Manual. I see the Ferrari uses a special rotor attached to the end of the cam. I'm not sure how it is attached to cam. Anyway, if the rotor had come off the end of the cam, you would expect both banks to be affected.

Here's a shot of a bent cam rotor on a Ferrari:

(Third photo)
https://www.ferrarichat.com/forum/posts/140047831/

 

This is what you should see at the trigger pins (pins 1 and 3 at the coil or what ever they are at the ECU). Pin 1 or 3 will be at 12 V. Then when the ECU switches the voltage will drop to zero, then rise slightly due to resistance in the primary side of the coil. When the ECU opens the circuit again there will be a large spike and a quick recovery to 12V.

The picture is from checking my 308 but there is no reason the 355 should be any different.

Still concerned about why there was a cam sensor code. OBD II isn't usually wrong. The cam sensor signal can be checked with the scope.

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That is exactly what I would do before replacing a very expensive ECU. I have a node light for checking injector/coil pulses that takes out the guesswork. But in this case, I think Grant has determined the wiring from the ECU to the coil is good, the coil is good and has a good 12V feed so I would lean toward either a bad ignition module (internal to the ECU) or some other logic influence that would intentionally take out the spark signal. Grant, did you confirm that you have injector signal for the dead bank? If there was no injector signal for that bank, then I would lean toward the logic.

 

If the injectors were firing without any ignition, you would get a lot of petrol smell. I guess there is a safety feature in the ECU which, if the ignition circuitry fails, will shut down the injectors.

 

I can't imagine Bosch building in a safety feature to stop injectors. But yes, you would have a strong fuel odor. I suppose the ECU may use the same drivers for the injectors as the primary coils so the failure would cause the loss of both. Does anyone know if the Motronic is EFI or is it sequential injection?

 

Has anyone checked the simple wiring connections even going back to ecu?

If you look closely often the female pins are spread open on the motronic connector block.

 

I would believe that if there was something logic related (like an SDU) that the protocol would be to shut down fuel for sure (the last thing you want to do is to push raw fuel down to a red hot cat) and probably leave spark alone. That would leave you with a more probable ECU issue.