Electronic Distributorless Ignition ... - EFI Dyno Tuning LC



Electronic Distributorless Ignition System

by Bruce Bowling



This section deals with the operation of the Ford EDIS Electronic Ignition Module. There is a lot of information on the modules on the web, but much of it is incorrect or incomplete. The information here was derived from direct testing on the bench as well as sources like the DIY-EFI list. Additional detailed information provided by John DeArmond and a few other key sources were very helpful in figuring out proper module operation.

All experimentation was done using an EDIS-8 module, Ford part # F1AF-12K072-AD1D07A, from a 1997 Crown Victoria (police-issue) with a 4.6L Romeo engine. Also, identical operation was verified with another EDIS-8 module, part # F5SZ-12K072-AA. The assumption here is that EDIS-4 and EDIS-6 modules also work in an identical manner - we are testing/verifying these modules right now. If you do go to a salvage yard looking for EDIS modules, you can find them most often mounted on the fender on the left-hand (drivers) side, near the hood hinge. You know that you have the correct item by looking for the EDIS-4 sticker right on the unit (or EDIS-6 or EDIS-8, depending on cylinders) Be sure to grab the connector as well, and you may as well get the ignition coil pack(s) to make your life easy. You can also obtain used units from the salvage web at - for EDIS-4, look for 1990 - 1993 1.9L engines, EDIS-6 on 1990 - 1995 4.0L engines, and EDIS-8 on 1990 - 1997 4.6L engines.

The engineers at Ford deserve a big "pat on the back" when they came up with this system - it is an excellent example of distributed control. In fact, the whole EDIS system handles the complete task of crank/ignition synchronization as well as current sourcing for the wasted-spark coils. The task of generating the desired ignition advance is performed by the ECU, or in our case MegaJoltLight. The interface between the EDIS and the ECU is extremely simple.

In operation the system is very simple. The crankshaft is fitted with a 36-tooth wheel, with one tooth missing in order to provide crankshaft synchronization. The EDIS system is a wasted-spark setup (i.e. two spark plugs fire which are separated by 360 "cycle-degrees" of a 4-cycle engine), so there is no synchronization with the camshaft. Near the crank wheel (radially-situated from crank wheel centerline with a 0.030 to 0.060 inch gap) is a Variable-Reluctance (VR) sensor - this sensor produces a bi-polar signal very similar to a sine-wave which is generated by the rotating crank wheel. This signal polarity is such that when the tooth tip is exactly pointing to the VR sensor, the resultant VR waveform is at zero potential falling from a positive to a negative polarity - i.e. a zero-crossing with a negative slope. This resultant signal is fed directly into the EDIS module, indicating crankshaft position (every 10 degrees crank). The thing to note here is that the EDIS module handles all VR signal processing. In fact, the EDIS module has a built-in VR signal hysteresis - when the VR signal is transitioning from negative-to-positive polarity (next tooth is approaching), the signal must reach 0.5 volts positive before the EDIS module will "arm". It then will "trigger" when the signal passes back thru zero from a positive-to-negative transition, when the VR tip is aligned with the crank wheel tooth. We have measurer and verified the hysteresis effect on the bench (in-circuit). This hysteresis helps prevent false triggering, and it is something to note when experimenting with the EDIS module.

With the VR signal, the EDIS module can synchronize with the engine crankshaft. Note that the missing tooth on the crank wheel indicates the absolute crank position. In practice, the crank wheel and VR sensor is oriented such that the missing tooth occurs 50 degrees before Top Dead Center for the EDIS-8. The EDIS-4 and EDIS-6 modules have different advance settings (need to determine these values from measurement). With this setup, the EDIS module will fire the ignition at 10-degrees advance as a default, unless the module receives a SAW command (discussed below). This 10-degree advance is constant, regardless of RPM. This functions as a limp-mode; in case the module never receives SAW commands from the ECU it will generate a useable (but not optimal) advance to get you home. This is an important feature of this system, and makes it very DIY-friendly and safe on an engine.

Here is a picture of the (simulated) VR signal generated from the crank wheel, and the EDIS-8 firing point for coil #1:

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When the EDIS module receives proper VR signal, it generates a 12-volt square-wave signal with a period linked to the next cylinder to fire. In other words when this signal (Ford-named PIP) transitions from +12V to ground, one of the ignition coils is firing. This signal follows the ignition coils, not the VR sensor (as indicated on some incorrect documentation floating around). So, for an EDIS-8 module, there will be four complete cycles of the PIP waveform for every 360 degrees crankshaft, or thirty-five VR signal cycles (not 36 because of the missing tooth). An EDIS-6 will yield three PIP cycles per every 360-degrees crank, and an EDIS-4 gives two.

This PIP signal is used as a reference to synchronize the generation of the SAW pulse by the ECU (in our case MegaJoltLight). The SAW signal is generated by the ECU and is an input to the EDIS module. This signal is a +5V positive-transitioning pulse, and the width of this pulse determines the advance that the EDIS module will use for subsequent ignition events. Note that the SAW pulse must be synchronized with the PIP negative-transitioning pulse - it cannot be applied asynchronously to the PIP signal, otherwise incorrect advance commands will be interpreted by the EDIS module. Also note that the SAW signal does not have to be sent on every PIP cycle - the EDIS module will remember the last SAW commanded advance and "remember" it for all subsequent ignition advance values until a new pulse is received.

Here is the proper relationship between the two signals:

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Question - how does the EDIS module obtain the advance value from the SAW signal? Simple - the width of the SAW signal determines the amount of advance generated by the EDIS module. A simple equation governs the width as a function of advance:

SAW (microseconds) = 1536 - (25.6 * Commanded_degrees)

So, the width of the SAW word in degrees is related to the desired advance by the above equation. At first glance, it looks kinda odd, but it does make sense (depending on the hardware generating the width). With a microcontroller timer peripheral, most timers use a counter 16-bits in length, and they have a mode known output-compare, which is used to make an output toggle when the counter reaches a comparison value. So, if one uses a 16-bit timer incrementing at a 1 microsecond rate, and uses a 16-bit comparison register to toggle the output, they can easily generate the required period. In fact, the numbers are quite easy to use - see the following table for example SAW advance widths and corresponding 16-bit timer compare values:

Degrees Width(us) High-order 8-bits : Low-order 8-bits

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10 1280 0x05 0x00

20 1024 0x04 0x00

25 896 0x03 0x80

30 768 0x03 0x00

40 512 0x02 0x00

50 256 0x01 0x00

55 128 0x00 0x80

The numbers now make a little more sense. The high-order of the 16-bit timer drives every 10 degrees, and the lower 8-bits drives the advance values in-between. This makes generation of advance widths very easy with a microcontroller. Those Ford engineers knew what they were doing!

The range of advance word is from 59 degrees (60 would be a pulse width of zero) down to 0 degrees - all of these have been measured on the bench. How does one measure this? Using a two-channel scope and monitoring the VR waveform and coil #1 output from the EDIS module, it is easy to see the relationship:

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The other part of the whole EDIS module is the multiple-coil drivers. First thing is that the EDIS module has the actual ignition coil driver built-in - the driver is not part of the Ford wasted-spark coil pack. The coil packs are just standard ignition coils, and could in theory be substituted with other coil-only packs. The EDIS-8 module has four coil drive channels - EDIS 6 has three, and the EDIS-4 has two. The EDIS module handles the dwell-time automatically, depending on commanded advance and RPM - another feature which makes the EDIS one of the easiest to use DIY setups.

The ordering of coil drive fire for the EDIS-8 is coil A, B, C, D, A, B, C, D, A... - it just round-robins thru each of the coil drives. This is important to know when setting up firing order for the destination engine.

O.K. - we now know enough to implement the EDIS module in an rugged ignition system. The EDIS ignition system is rugged - the module mounts under-hood and will survive engine-bay temperatures, water, freezing, etc. And with only two wires going back to the MegaJoltLight box (PIP and SAW), wiring is extremely easy.

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For reference, here are the wiring diagrams for the various EDIS modules, starting with EDIS-4:

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EDIS-6 wiring:

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EDIS-8 wiring:

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updated: 11-28-02 - bbowling@

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TFI SPOUT --> EDIS SAW (pin 3)

TFI PIP --> EDIS PIP (pin 1)

TFI Ground --> Ground (pin 7 or 10 or both)

TFI Ignition On --> EDIS Ignition On (pin 6)

Coils A-B-C-D --> EDIS Pins 8,9,11,12

Crank Sensor --> EDIS Pins 4,5, and shield goes to 7.

TFI yellow/tan tach signal goes to EDIS pin 2.

Which way do you want to go?

Explorer/96-98 GT Coil Packs and still have plug wires or go wild like me And go Coil on Plug

Now you have 2 Ways of running this... You wanna stay OBD 1 or 2?

There’s a lot of factors.. Ill give you the run down of my wife’s car.. Its OBD1 running without an tuning software.

408W.. If you don't know, Ford never made a Cam Sync sensor for a 351W nor did they make a trigger wheel. What I did was took a 3.8L V6 99+ Cam Sync and removed the shaft and installed it into a Explorer Cam Sync 00+ 5.0L. There now you have a 351W Cam Sync.

Now we got that part down. Now you if staying OBD1 and stock Computer you will need a Ignition Module. For this you need an EDIS8 module you can get off of crown vics 93-96ish and t-birds 4.6Ls. For the Trigger wheel I bought a new Explorer Balancer and took my balancer to my machine shop and they pulled the Trigger wheel off and installed it onto the back of the 28oz balancer. They made a steel ring so they could press it onto the new balancer.

Wiring the fun part.. You can use the stock wiring and cut/hack and make it work. Or be an idiot like me with a lot of time on his hands and make your own based off a OBD2 harness converted down to OBD1. Meaning changing the EEC connector. Still a lot of wiring and repining but the 94-95 V6 already has the Ignition module connector built on. Now for an Injector harness I would recommend a 96-98 GT or 99-03 GT pending if using coil on plug or coil packs.

No matter which way you go it'll take time. I'm actually thinking of producing some cam syncs and wiring here soon if I get more time. Since I have it down to a science and no what to do.

My Opinion the Coil on Plug system is great. Loved how it idled and ran.. After driving it I will never go back to distributor ignition.. I'm going to be building another one for my 302 car this winter. For now going to run a distributor.

The Cam Sync Sensor is what drives the oil pump shaft.. Look at the 5.0L Explorers and Mountaineers. They don't use distributors they run by cam sync and trigger wheel. I would run the AEM with it, because with the AEM you can delete the MAF and install a MAP sensor and go speed density. Going to Coil on Plug route is very expensive do to your looking anywhere to 45-90 a piece for a coil. times that by 8. Granted Accel and MSD both now make them so the prices are coming down but you’re still talking in the range of 400-500 bucks just for the coils. I recommend on a budget (who has one of those and drives a mustang) doing the dual coil pack setup like you find on the Explorer/Mountaineer or 96-98 Mustangs. Down fall is you still have plug wires.

The problem is no one makes a Balancer with the trigger wheel mounted like the explorer in 28oz imbalance. Now if your N/A staying that way you can have the rotating assembly done in 50oz and just run the explorer balancer. Also another piece needed from the Explorer will be the timing cover. Need it just so you can mount the VRS sensor.

I've spent a lot of time (years) working on this. I just need to get a hold of a few people to see if they can source me the harnesses to make them.

I do want to mention something on my setup.. If you decide to keep the stock computer OBD1 you ignition either coil-on-plug (COP) or the dual coils will be a waste spark setup. Meaning 2 cylinders fire at the same time. If you go OBD 2 and use a 99+ Computer then I would defiantly say going COP do to it can fire each coil individually. the 99+ system doesn't support the dual coil packs you would need to run a 96-98 GT Computer. And down the run you could always change and keep the OBD 2 96-98 Computer but just wire it up for a Waste Spark setup.

I want to post the link that got me thinking of even doing this.

I would not recommend going to the OBD 2 setup if you have no way of tuning the EEC just because now you'll need to turn the rear O2 sensors off and some other little things here and there. Also pending the obd 2 computer year you have to tune for the return fuel system since 98+ is return less..

It’s a big headache but once you sit down and figure it out it’s not too bad.

Danny (SorsCode on Stangnet)



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Getting the advantage on Distributor-less ignitions Submitted By Dave King

High Performance Ford vehicles that run distributor-less ignitions have EDIS electronics. Many people are unaware of EDIS and don't know much about it. EDIS comes into play when a racer starts getting serious about their vehicle.

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EDIS's 2 main functions are generating PIP and SPOUT signals to the engine management system. In a nutshell the module gets a crank trigger and position signal from the trigger wheel and then the EDIS-8 module organizes the firing order and triggers the coil packs in the proper order. It’s considered a "waste spark system" meaning that it fires at compression and exhaust strokes near TDC. As long as you organize the wires accordingly, it could conceivably run any firing order you want on a typical 4-6 or 8 cylinder. The EDIS-8 unit puts out a PIP signal, which is what most fuel injection systems use to trigger the injectors and simply determines how fast the engine is rotating. It then has a SAW wire (Spark angle width) also know as the spout, this is the signal that tells the EDIS module what to do for timing.

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Profile Ignition Pick-up is the term used for the signal sent from the (EDIS) to the (ECM). This signal is the digitally modified signal that originated from the Crank Angle Sensor (CAS) in an Alternating Current (AC) format. The PIP signal into the ECM is a squarewave switched at 12 volts and is the ECM's reference for the engines speed and position. The PIP signal when received by the ECM can then be modified to take into account the ignitions timing advance. This returning signal to the EDIS unit is called the SAW signal as is in the form of a 5 volt squarewave. Both signals can be seen in the example waveform with the PIP signal in blue and the SAW signal in red. The Ford EDIS system is an enhanced version of the DIS ignition system. The major difference is that the DIS system requires a CID (Cylinder Identification; cam phase) sensor in addition to the crank driven toothed wheel. The EDIS system only requires a 36-1 toothed wheel and VRS (Variable Reluctance Sensor) crank sensor. The EDIS system is comprised of an EDIS module, crank wheel, crank sensor, and coil packs. This system is completely standalone and will properly ignite 4, 6, and 8 cylinder engines using the wasted spark method. The system relies on the ECU (Electronic Control Unit) to control spark timing, but will function if no ECU is connected. Spark Angle Word (SAW) is the response by the control module to the EDIS module after the control module does its usual job of calculating the advance or retard of spark timing. In EDIS, SAW is the same kind of signal as SPOUT is to TFI-IV and DIS. In the EDIS Module, the microprocessor decides which coil to fire at what millisecond -- coil selection and spark timing. In addition to the coil-driver outputs, the EDIS Module confirms its timing by sending the IDM signal to the control module, a signal that also operates the tachometer.

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The downfall of the stock EDIS module is that it was never intended for higher RPM applications, because it was designed for powerplants with a 6500 redline. EDIS started in the early 90's and was used in Lincoln Mark VIII or Lincoln Towncar application where they used EEC IV Generation computers with distributor-less ignition. Fast forward to 1996 and the introduction to EEC V OBD II computers, the EDIS electronics are built into the computers electronics. EEC V computers did not have the need for a separate device. When racing maniac's such as myself with distributor-less ignitions ditch the factory computer, you need to use a separate box that will generate PIP and SPROUT signals to the engine management system that one decides to purchase (Speed Pro, Gen VII or EPEC).

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What racers did (including myself, Lideo, Tim Palmer, Reggie etc) was use an EDIS box out of a Lincoln Mark VIII (the only one sold by Ford). The downside was that once Engine RPM'S reached 8000 rpms, the PIP signal attenuates to the point that Speed Pro would not recognize it and "guess "In real time". On my datalogger once 8000 rpms would be achieved the datalogged RPMS would show something like this (2500, 6200, 4740,3954, 7000, 5400). This erratic change in RPM would cause the car to misfire and basically simulate spark blowout. Forward to Mid 2001. FAST (Fuel Air Spark Technology), the company that now owns Speed Pro came out with their own EDIS module. In order to use the new FAST box, () you have to run sequential injection (an upgrade needed on Speed PRO users that run Batch Fire) because it needs to see an input from the cam position sensor (Batch fire doesn't use cam position sensor). Using the FAST EDIS also requires using a magnetic crank trigger wheel and pickup that must be bolted on the crankshaft pulley. The stock crank trigger wheel and pickup can no longer be used. Once these upgrades are complete, the problems associated with the EDIS box itself are eliminated.

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Also around the same time the new EDIS box came out, MSD came out with a HO version of the DIS 4 box that has been so popular. The HO model produces an incredible 170 milliJoules of spark energy with 470 volts going to the coil packs. This is up from 115 milliJoules in the standard DIS-4 box and more energy than an MSD 7AL-2 or 7AL-3. Therefore any limitations with EDIS ignition should be in the coilpacks themselves (yet to be tested). A few companies make aftermarket coilpacks such as Accel and MSD but they are only "slightly" higher in output. I'm hoping that the stock coil packs will not be a limitation. Ford uses EDIS in Indy car technology so I think they will be fine.

Coil packs versus Coil on plugs It is my feeling that Coil packs will support more horsepower. It is still is unanswered as to how much horsepower either system will support. The reason I say this is because Tim Palmer has made the most horsepower so far with coil packs at around 1100 bhp. But he only did that for a very short time. Nobody has really made over 1000 bhp with coil on plugs (at least from what I am aware of) With Bob Trinanes and myself both going back to coil packs, we will find out that answer.

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