My dizzy was leaking oil and knowing how tedious replacing the seals on these, i decided to convert the ignition to distributorless system using Ford EDIS-4 control module. Ford EDIS is basically a wasted spark ignition system using 36-1 trigger wheel and VR pickup sensor, available for 4, 6 and 8 cylinders. You can get the full kit from Ebay for less than 60 bucks, containing the control module, VR sensor, trigger wheel and coilpack and spark wires. Don't worry about the supplied trigger wheel diameter as with some machining, it should fit perfectly to 4A-GE crank pulley.
Why Ford EDIS when my Megasquirt is fully capable of handling wasted spark system on its own? First, since my MS is based on v2.2 board, it doesn't have a built-in coil driver (VB921). This means i have to make the circuit and integrate it to my MS or get another igniter module which supports wasted spark system (i was told an igniter module from Mitsu's 4G63 can do this). With Ford EDIS, i don't have to do any of these since everything is done by the EDIS control module. Second, EDIS has this wonderful feature called limp-home mode which is a fail-safe system that ensures your ignition is still working although your ECU fails to feed signal to the EDIS module. This means EDIS can function separately on its own. The drawback is that on limp-mode, the ignition is locked at 10deg BTDC. The engine won't run efficiently that way but at least you get to drive home to fix the problem. I won't discuss how EDIS works as the Megasquirt website covers that in detail.
Below is the step-by-step on how i did my conversion.
Trigger Wheel Installation and VR Sensor Bracket Fabrication
Below is the basic idea taken somewhere from the web.
Trigger wheel is placed at the pulley's front and the VR sensor bracket is bolted to the AC and PS bracket bolt holes on the engine block. Yes, no PS and AC for me.
This part is the most error-prone work as you need to ensure that you place the trigger wheel's missing tooth on the correct position on the crank pulley before you weld them together. Also be careful that the trigger wheel's centered to the pulley to avoid premature main bearing failure from excessive vibration.
With EDIS-4, the missing tooth has to be placed 90 deg (or 9 teeth) ahead of the tooth facing the VR sensor when the engine is set at TDC. If you follow the sample picture above which places the VR sensor on the right-most exhaust side of the 4A-GE engine, the missing tooth will be facing downward at TDC as this engine rotates clock-wise. Here's an illustration.
To achieve this, here's what i did.
1. Set the engine at TDC
2. Mark the right-most part of the pulley with a marker. This mark will be aligned with the 9th tooth of the trigger wheel.
3. Mark the 9th tooth from missing tooth (little "x" with a marker should do). Ensure that the missing tooth faces downward.
4. Take the pulley off the crank shaft. You have to find a way to stop the engine from rotating to be able to turn the bolt holding the pulley OR you can do it with the totally unsafe way of sliding a pipe on the socket wrench handle so that it's long enough to reach the floor as to allowing the floor to stop it from turning, pull off the ignition coil spark wire and yank that bolt off by turning the starter.
5. With a lathe, increase the inner diameter of the trigger wheel so that it's the same as the crank pulley's. This will help you center the trigger wheel to the pulley. (see note below)
6. Align the 9th tooth of the trigger wheel to the pulley mark you made earlier while making sure the wheel is centered.
7. Tack weld, check for center and final weld.
8. Check the "x" mark on the 9th tooth on step 3. This will be also your reference when fabricating the bracket to position the VR sensor.
9. Reinstall pulley and ignition coil spark wire.
10. Get the engine running and check whether the trigger wheel is off-centered.
11. Turn engine off and set at TDC.
12. Fabricate the VR sensor bracket, ensuring VR sensor faces the tooth with the "x" mark you made earlier on step 3. This bracket must be very sturdy and rigid. Make strengthening ribs if you must. Sensor should be spaced within 0.75-1.00mm from the tooth edge so any vibration from the bracket when the engine running might get the sensor to foul the trigger wheel and destroy it. The difficult thing about making the bracket is there are two axis that you need to calculate. First axis is parallel to the engine block length and determines the VR sensor is centered to the trigger wheel and the second axis determines the VR sensor is spaced within tolerances from the tooth edge. A cardboard model does wonders to save you precious metal sheets. Don't forget the notch for the oil pump.
Control Module and Coil Pack Placement
Pictures do enough talk here.
Coilpack sits on the original engine mounting which now is not used as the engine is mounted longitudinally. Original coil pack bracket is modified to suit.
As previously mentioned, Ford EDIS has limp-home mode which allows the system to work independently from whatever ECU is driving it. This allows you to make a trial wiring to make sure the system works and you place the VR sensor correctly. Just make sure the engine was running before you start the conversion. Basically trial wiring is just connect the VR sensor, coilpack and control module together, supply power to the module and start the engine. The timing must be fixed at 10deg BTDC this way. If it's not, you must readjust the VR sensor position. This is important as any offset will also yield the same offset value to your MS Spark Map. For example, on limp-home mode you find that the timing is fixed at 15 deg BTDC. This means all the values on your MS Spark Map will also actually run 5 degrees more advance. Here's the wiring diagram taken from MS website.
Pay attention to the VR sensor polarity. If you follow the basic idea picture above, "+" side of the VR sensor will be the lower pin (closer to the oil pan). Connect this to pin 6 of the module. It won't run if you wire it incorrectly. Also pin 10 of the module is wired to the cylinder 1-4 side of the coil pack.
I don't know how crucial it is to run shielded wire for the VR sensor but i did anyway. Do it once, do it properly. I know for certain the PIP and SAW line going to the ECU needn't shielded wire as mine is running well this way but your mileage may vary. Engine bay is really a battleground for EMI. Make sure the shield is only grounded on control module side (pin 7). Don't ground the shield on the VR sensor side or you'll defeat the purpose of having a shield.
Once you finish wiring, start the engine and check the base timing. 10 deg BTDC? Good. Head on to the next step.
Megasquirt Internal Circuit Mod
This is when you start messing with the engine's original configuration and to me it's the point of no return. Once you get to this step, falling back is a PITA so make sure you know what you're doing.
For me, there are two parts of the Megasquirt internal circuit that need to be modified: ignition input and ignition output. This is because my engine was previously running with a ground-off 4-tooth distributor pickup wheel, an LM1815 VR conditioner and the original 4A-GE VAST igniter. Remember that my MS is based on v2.2 schematic and running MS1-Extra firmware. Here's the mod you need to do based on MSExtra website guide.
Ignition Input (PIP Signal)
I use 680 ohm for D8 and it's working fine.
The main difference for me is EDIS PIP signal works with "falling edge" while my LM1815 VR conditioner works with "rising edge" signal. So, previously the flow is LM1815 output --> 680 ohm resistor --> anode 4N25 (pin1) --> cathode 4N25 (pin2) --> ground. For EDIS, the flow must be +12v --> 680 ohm resistor --> anode 4N25 (pin1) --> cathode 4N25 (pin2) --> EDIS PIP line (pin 1 EDIS control module).
Ignition Output (SAW Signal)
My MS originally drives the 4A-GE VAST igniter and based on MS website, there should be a 5v pullup resistor to do so. Same applies if the MS is to produce SAW signal for EDIS control module so i thought i didn't have do any mod. However, to my surprise, there was no pullup resistor so i had to do the mod shown here.
I use 820 ohm for the pullup resistor as 750 ohm is an awkward value that i couldn't find anywhere. Works fine. Basically i solder one end of the resistor to the serial connector pin and jumper-wired the other to a 5v source, minimizing soldering to the PCB.
Once done with these hardware mods, you need to change the software configuration using Megatune so that MS works in EDIS-mode. Head on to MS website for this. This is the link for MS1-Extra.
Final wiring is just connecting the PIP (pin1 control module) and SAW (pin 3 control module) to Megasquirt. As said previously, i didn't use shielded wire for this and it's running fine, able to reach high RPMs without stuttering. Laziness prevails here. It's a good idea to install a socket and plug to the SAW line so you can disconnect the line anytime and simulate limp-home mode to check the base timing. 10 deg BTDC, remember?
Done? Recheck the wiring and cross your fingers. Start the engine and if it runs, enjoy not having to replace your dizzy oil seals regularly since it's awkwardly placed near the exhaust manifold which is more than happy to fry the seals anytime. You can now pull out your dizzy and cover the hole with some plate. Plus, the EDIS coil produces fatter spark than the stock one, or so i was told.
What about your now dead tachometer? Again, if you read the link for MS1-Extra i gave above, it will tell you how to tackle this. If you're lucky, you'll just have to connect pin 2 (IDM) of the EDIS control module to your tach wire and it will work.. but most probably it won't so you'll have to do the diode method. I have to be honest, right now my tach is working with the diode method but erratically. I didn't use the 15v zener though. Doubt it will make any difference. I have yet to find a way to make it more stable.
Here's more ideas on how to make your VR sensor bracket for your 4A-GE, taken from all over the web.
Also, if you're CERTAIN that you won't be using PS or AC, you can ensure the trigger wheel is centered to the pulley by machining off the ridges for PS and AC belt and fit the trigger wheel here. You can also make an interference fit this way, i.e the trigger wheel inner diameter is actually machined a hair smaller than the pulley outer diameter. Boil the trigger wheel in molten lava and put the pulley on north pole to fit them together. Or hot water and freezer should do just fine. Once they both reach room temperature, you'll have a strong fitment. Here's the idea.
*** edit Oct 5th 2011 ***
Just thought i should add more pics of my setup. Below is the VR sensor bracket. You can see the notch to clear oil pump housing and the added extra metal plate rib on the center to increase rigidity. My bracket was made of an old desktop computer tray, if i'm not mistaken. I just found it lying around the house and thought it'd be great as a bracket.
Below is the big picture. You can see all the parts in one shot.