As stated before, the XJS started it all with (amonst others) its ignition problems. At the time, it still had its original OPUS ignition system and when this reached a certain temperature, it would stop working, leaving you stranded for about 30 minutes where you were. An attempt at having the dissy modified with a modern VR based ingition module resulted in the vacuum advance mechanism being disabled - which is OK for a race engine but not ok for a road car where you also want the best economy. This motivated me to find an electonic ignition solution and this is where Megasquirt and EDIS appeared on the scene.
EDIS can be controlled either by Megasquirt (which controls spark and fuel) or Megajolt (spark only)
EDIS operates on the principle of “Wasted spark”. Typically a double ended coil pack is used but I’m rather sure that with proper selection of hardware a coi-per-plug or coil-over-plug solution could also be implemented (albeit still on wasted spark principle).
What I like about the EDIS approach is
1) the simplicity of installation and wiring
2) uses only one Megasquirt output - leaving others for NOS, fans etc
3) reliability - the EDIS modules are most reliable
4) keeps high voltage ignition signals away from MS
5) reduces MS processing
6) You can position the VR sensor anywhere around the trigger wheel i.e. where it will mount easiest and then you can position the trigger wheel the correct amount of teeth away. The missing tooth does not have to be at TDC. The crank must be at TDC when the VR sensor is pointed to the correct tooth. Clear as mud?
7) most of all - EDIS produces a SERIOUSLY POTENT SPARK - see video - strong enough for any amount of boost you may wish to throw at it
EDIS disadvantages (those I know of)
1) Can only use spark retard for ignition based rev limiting (you can still use various fuel cut methods) which is not very effective as with B&G fw you can only retard 25 degrees and with Extra fw you can only retard 12.5 degrees, neither of which is enough or very effective.
The DUAL edis concept
EDIS-8 is the “biggest” EDIS system and can handle a V8. For a V12, such as the Jaguar V12 it possible to use two (2) EDIS-6 systems where each EDIS-6 system handles ignition of one bank of the engine. On the Jaguar V12, the B-bank runs 60 degrees after the A-bank and that is why the VR sensor for the B-bank EDIS needs to be mounted 60 degrees after the A-bank VR sensor. This is also why an additional electronic module is needed to make the B-bank EDIS advance correctly. See below.
The Dual EDIS concept can be used as follows:
2 x EDIS-4 systems to control a V8 (this could make sense if you intend implementing coil-per-plug or coil-over-plug)
2 x EDIS-6 systems to control a V12
2 x EDIS-8 systems to control a V16 engine
“DESC” (Dual EDIS Signal Conditioning) module
Megasquirt sends a signal called “SAW” to the EDIS module for the A- bank but this signal is not correct for the B-bank and needs to be modified. I have developed a module to do this correction called “DESC” (Dual EDIS Signal Conditioning) module.
DESC takes the SAW signal coming from Megasquirt (or Megajolt) modifies it and then sends it to the B-bank EDIS module to ensure that the B-bank module also advances timing correctly. DESC also provides a 12-cyl tacho output (if needed) and can also control a relay providing 12V feed to the injectors - if so desired. The latter to ensure that the engine will NOT run on only one bank (yes, it actually can) as running on one bank may severely damage catalytic convertors. This same approach can also be used to implement dual EDIS-8 for an ignition solution for a V16 or 16 cyl engine.
Wiring diagram for the Jaguar dual EDIS-6 system here
Instructions (for US Letter) for implementing dual EDIS here
Instructions (for A4 paper) for implementing dual EDIS here