308 GTSi Ignition problem

Please clarify this result -- do you mean:

1. You swapped DigiPlex ECUs, and you still had no spark on the front bank, or

2. You swapped Digiplex ECUs, and now the rear bank had no spark?

If #1 = most likely either a bad front bank TDC sensor or bad front bank coil (and since you already replaced the front bank coil, must be the front bank TDC sensor) -- but both your DigiPlex ECUs are OK.

If #2 = bad DigiPlex ECU.

(assuming that you don't have some rare wiring problem)

PS it's better to call them the "1-4 bank" and the "5-8 bank" to minimize miscommunication -- sometimes people have different definitions for "front" and "rear" depending on where they are standing and which way they are facing.

 

As Steve said, clarification is needed!

"If #2 = bad DigiPlex ECU".

Or bad/corroded connections at the ECU. Common problem considering their location.

 

If the coil's secondary output is directly shorted to ground (which is sort of equivalent to running solid non-resistor ignition wires + non-resistor extenders + non-resistor plugs), this can put stress on the ECU transistors switching the (large) primary current in the coil (and is why your stock ignition system is designed with spark plug wires and extenders that have some non-zero impedance). When your rotor "exploded" did the center carbon button come into direct contact with the distributor shaft?

However, even if the worst possible thing happened to one bank's rotor/secondary, that wouldn't explain why you now have two dead ECUs (if one ECU never saw the "bad" rotor condition). Another component that can take out both banks together is the Engine Speed/RPM Sensor (that measures the ring gear teeth passing by). What I would do is:

With key "on", everything plugged in as normal, and engine not running:

1. Measure the DC voltage between the G (yellow) wire(s) connected to terminal 15 of each coil and ground = should be +12V DC (confirms that you've got electrical power to the coils)

2. Measure the DC voltage between the G (yellow) wire(s) connected to pin 8 of each DigiPlex ECU and the N (black) wire(s) connected to pin 9 of the same ECU = should be +12V DC (confirms that you've got electrical power to the DigiPlex ECUs)

If you pass both those tests -- with everything plugged in as normal and cranking the starter motor:

3. Measure the AC voltage between the R (red) wire(s) connected to pin 3 of each DigiPlex ECU and the RN (red/black) wire(s) connected to pin 2 of the same ECU = should be something like 2V AC (or greater) at both ECUs. (This checks the Engine Speed/RPM Sensor output)

4. Measure the AC voltage between the L (blue) wire connected to pin 1 of one DigiPlex ECU and the V (green) wire connected to pin 5 of the same ECU = should be something like 0.2V AC (or greater). (This checks one TDC Sensor output)

5. Measure the AC voltage between the N (black) wire connected to pin 1 of one DigiPlex ECU and the G (yellow) wire connected to pin 5 of the same ECU = should be something like 0.2V AC (or greater). (This checks the other TDC Sensor output)

If all that seems OK, and you can find no other wiring problem, contact the ECU Doctor :

http://www.the-ecu-doctor.co.uk/

or

http://www.ecudoctors.com/ferrari-308-1980-1984.html

If you've damaged some non-proprietary electrical component inside, they should be able to test/fix. (But please post feedback about your results from tests 1-5, and Good Hunting!)

PS Assuming that you have a euro 308QV (based on the 803A), your schematics show that you have an ignition diagnostic socket where the DigiPlex ECU connections may be more easily found/touched -- see the ignition system schematic in Section 3 or the wiring diagram in Section 5 of your OM.

 

excellent post by Steve...as always ;-)

just to "visualize" Steve`s description of point 2-5, I will add two pictures of the marelli ecu connectors and the corresponding wire colours - exactly as decribed above !

(never mind the taped connectors and the spliced wires - for the tach signal - since I switched from marelli to electromotive xdi)

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If the rotor arm breaks, the secondary HV voltage has no ground potential to discharge, the stored energy can then damage both the coils secondary windings insulation and the coil itself due to the thermal stress after some time. The heat also changes the primary field saturation, which can overload the output stage in the ECU as the charge/dwell times are longer, due to the missing discharge. Not an issue if this only happens for a minute or two, but if the setup is run in that way for more than 10-15 minutes, a defective coil and output stage is quite likely.

But as Steve already said, it's unlikely that this damaged both ECUs.