308 Quattrovalvole Ignition Timing Diagram

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1. 

   In the course of doing a major service on this car and getting it back on the road, I noted that there is no advance mechanism inside the distributors. This is a USA car with twin distributors. My question is this: do these engines just run at full advance set in from idle, or does the electronic ignition also regulate spark advance? I didn't think electronic ignitions had that capability in 1985, but perhaps I am selling them short. Very interested to hear comments on this.

   My apologies if this has already been asked and answered. I couldn't find any information in the few 308 books I have.

2. The ignition timing curves are controlled by electronic modules. There is a separate module for the front and rear banks. Ignition timing is non-adjustable.
   The modules are mounted under the carpet in the trunk (drivers side).

3. 

   My 308, a '77 GTB (#22963) has a mechanical advance mechanism inside of each of the two distributors.

4. 

   Thank you both very much. Evidently when they went to electronic ignition, the advance mechanism changed to electronically regulated. I appreciate your answering my question.

5. From the fuel injected cars of 1980 forward all Ferrari V8 had electronic advance. The 12s started it with the 412 and the TR.

6. 

   Professional Ferrari Technician

   The 1975-1979 carburated 308s used conventional ignition with the mechanical advance mechanism built into the distributor (Euro dry sump)/distributors (wet sump).

   The fuel injected 308s from 1980-1984 used a Marelli Digiplex ignition system with two control units (one for each cylinder bank/ignition coil). These have vacuum input that controls which one of 8 different advance curves are to be used (engine RPM vs degrees of advance). The final stage of the ignition system that switches the ignition coils on and off is incorporated into each ECU. This is the part of the system that is under the most load. So if it fails, you will need to repair your control unit or replace it.

   The 328s from 1985-1988 used a Marelli Microplex ignition system, with one control unit for both banks. This has 9 different advance curves depending on the vacuum input to the ECU. The final stages that switch the coils on and off are separate from the control unit. They are bolted to the top of each ignition coil. Ferrari calls them "power modules", and you can purchase them separately if they go bad.

   The vacuum input to both types of electronic ignition system is taken from the small port on the left rear of the intake plenum near the oil filter. If you disconnect the vacuum hose from the port while the engine is idling, the idle speed should increase due to the change in the advance curve selected, increasing the advance.

   On the inside of the left rear sail panel in the engine compartment, there is a black plastic electrical socket with a plastic cap on it. This is the diagnostic connector for the ignition system. The Ferrari dealership would have had a Jofatron tester that would be plugged into this connector and in a few minutes you could check the advance curves of the ignition system. Ferrari of San Francisco still has their Jofatron tester. I would be willing to bet that there are very few Jofatron testers remaining at any other dealerships.

   There is a very good description of each system with a graph of the advance curves in your owners manual.

   Brian Brown
   San Francisco Motorsports

7. Brian I think the 1980-1985 has the Digiplex and the 1986-1988 has the Microplex

8. Out of curiosity, how does the micro switch mounted on the throttle housing affect timing? (1988, 328).

9. Without referring to the book I do not think it has any timing function. It has an influence on fuel mixture via control pressure modulated by the frequency valve.

   I see you are in England. Your cars have no frequency valve so the real answer is I have no idea without looking it up.

10. Can't recall ever seeing this explained well (or even at all) in the F documentation, but (for both US and euro versions) if you compare the idle timing specs given in the table (i.e., ignition timing at idle with throttle microswitch closed and vacuum connected), it is retarded vs the ignition curves shown in the graph for the same condition. For a simple physical test, at warm idle, just unplug the throttle microswitch (creating the open condition) = the idle speed should increase (if the microswitch is working/set-up properly).

11. 

    Professional Ferrari Technician

    The idle contacts of the micro-switch are only used as an input on the 328 ignition system, not on the 308 system. There is one advance curve with high vacuum input and throttle contacts closed in which the ignition timing is significantly retarded when compared to the 8 other advance curves, even at high RPM. This would indicate that they wanted to retard the timing on deceleration (throttle closed, high vacuum) at all RPMs, for what reason I don't know, maybe emissions?

    Brian Brown
    San Francisco Motorsports

12. Probably retard at idle, not so much decel. Idle is a very dirty mode and retarding timing reduces HC a lot. On cars with frequency valve there is also a mixture component to the idle contact. I'd have to review the books to speak to any of it very well.

13. Perfect, that's exactly what happens!

14. Yes, it's an easy, simple test to do on the Microplex systems after adjusting/readjusting the throttle microswitch to confirm that its properly closed at idle. As the Brians indicated, this ignition timing change doesn't apply to the Digiplex system, but, on any of the "with Lambda" systems (whether K-Jet with Lambda, KE-Jet with Lamda, or KE3-Jet with Lambda), the closed throttle microswitch at idle also "tells" the injection ECU(s) to limit the "swinging" of the signal(s) going to the frequency valve or EHA(s) to limit the mixture change at idle and minimize any noticeable RPM "hunting" at warm idle when running closed-loop.

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