GM HEI computer controlled distributor

[Machismo]

Next step is to make the ignition work. I have a large housing GM HEI distributor that is typical to the 80s V8 engines. It has integrated coil, eight teeth pickup module with no missing teeth and an ignition module. So it can give spark even without any ecm in the car. But of course normally ecm controls the timing. It dows it by sending different width pulses to distributor, where the ignition module advances or retards accordingly. The distributor shaft is rotated via gears by camshaft, so spark automatically goes to the right cylinder.



Here is the original distributor schematic



So basically I'll probably install one IGBT ignition driver to my 3.6 board and try to control the integrated coil directly. I already have a 60-2 vr sensor at the crankshaft so distributor pickup module is not needed for position and Vems does the job of the original ignition module also. If I had direct ignition with eight coils, only then I would need some camshaft position sensor.

As usual, feel free to correct me if I'm wrong.

Currently there are five wires connected to distributor: ignition switched +12v, ground, tachometer out(4 pulses per revolution reference signal), electronic spark timing(est) bypass and electronic spark timing.

After conversion there will be +12v, ground, coil control signal and maybe tachometer out. If that does not work, I can also get tach from Vems board.

[gunni]

The main purpose of having cam shaft sensor is for injector closing angle adjustments, this can result in general improvements with better fuel economy, but requires adjusting.

[jrussell]

I don't really see a question here. Are you asking for confirmation you're on the right track?

Here's how I have my boat set up:
COIL to ECU WIRING:

   1. G (Ground): Wire to analog GND (ec36-26)

   2. B (5V): Wire to Hall power (ec36-28)

   3. R (Signal from Reluctor/Module to ECU):  Wire to primary trigger (ec36-27)

   4. E (Signal from ECU to HEI Module to fire the coil): Wire to a logic output on the ECU


You don't need the R going to EC36-27 since you have a crank trigger signal already. So just use G, B, and E. You don't need to use an IGBT to drive the coil, or you can remove the HEI module completely and just drive the coil direct with an IGBT. Whatever your preference is.

[Machismo]

Thanks, actually I didn't have any questions yet, just documenting as I go along. 

I had a small vacation after starting the thread, but now I made some progress with the car.

First I checked how the timing works with the original hei system, and I noticed that normally at idle there is a about 10 degrees of basic advance with est wire disconnected. When increasing rpm (est still disconnected), the ignition module sharply increases the advance 8 degrees more when above 1100 rpm, so there it's 18 degrees total.

After that I connected the original ecm and est wire and the idle advance was 22 degrees total. If I blip the throttle very fast, I can see the timing drop to 12 for short moment. Reason is unknown to me.
And when increasing the rpm to 3000, the advance also increases to 34 degrees total. Above that rpm not much change happens, except maybe it slowly gains few degrees more, probably because timing chain streching a bit or something else mechanical.

[Machismo]

I decided to bypass the original ignition module because the end result is more simple as a whole and maybe the spark control is also better when driving the coil directly. The downside is that there probably will be more electric noise introduced to the board and sensors? Until now, when I was only driving the injectors, there have been zero problems with noise.

There's only one coil to control, so one fet will be installed to the board. I checked what I have in store and initially thought all four types are suitable for ignition but they are not. On closer inspection the two on the right are for injector or wb02 duty.



For some reason I found nothing when I googled the differences of the two on the left, but I'm guessing both are ok and I blindly choose the DD30AE V3040P.

I mated it with single heat sink like this, since I've heard that unlike injector drivers, IGBT:s need some cooling.



Fet was installed to the IGN 0 location.



IGN 0 is connected to the EC36 pin 35 (ignition output 00) and I used a plain single wire to connect it to the distributor. There are three separate connectors (marked purple) at the coil, of which one has three pins. The wire was connected to pin number one, which of course is the coil trigger. On the other hand, that is also connected to number 4 which is the tach output.



The original 12v feed was connected to number 5 and ground wire from engine block to number 2. Three and four were left empty at this point.

I also disconnected the four pin connector at the base of the distributor, since any of the electronics there(ignition module etc) will not be used anymore.

[Machismo]

With the wiring set, I took a look at the Vemstune ignition settings. At first it was logical to think that one output in the config was enough



But that was not the case. Turns out you could select the same driver eight times and therefore get eight sparks per camshaft rotation. Notice that firing order does not matter here, we just want eight dummy sparks, the distributor will deliver them to right cylinders.



For testing, I turned the crankshaft to the top dead center (TDC), because that's when the distributor rotor points to cylinder #1. After that I inserted a testing light between the plug wire and plug, which lights up when there is a spark, so the engine does not have to be even running. I also enabled the Testing mode and pressed the Test buttons. Does not matter which of them is pressed, all will create a spark.



At first there was nothing, but I remembered that there are two different 0 degree positions, but only one will have the camshaft in correct phase so I rotated the crankshaft another 360 degrees, after which I got spark to the #1 cylinder.

[Machismo]

Just getting a spark is not enough, it has to be properly timed also. Since my 60-2 trigger wheel is attached in random position to the crankshaft pulley, I had no idea what is the correct timing setting in degrees. So I disconnected the injectors and asked my friend to crank the engine, meanwhile I was looking at the marks at the damper with timing light connected to the #1 plug wire.
I noticed that the 0 point is about 50 degrees away from where it should be and after changing the "tdc after the trigger" setting accordingly, I could try start the engine with base timing set to 0 degrees.

However the engine didn't start and I noticed the numbers were wrong in the reference tooth table. I edited it and the car started. The correct settings looked like this



I had no need to add any special delays so this was left untouched



Here is the ignition settings menu. When the car was idling, I tested different dwell settings. When 1.0ms or less the engine would run bad or stall, so I just added some extra. Maybe 1.5ms would work also. If some beginner is reading this, dwell is the amount of time required to charge an inductive coil to its maximum energy level...

[Machismo]

All is well you might think? Not quite. The engine runs but there are huge problems with the laptop serial connection. It's now disconnecting all the time.

I thought about it and realized that originally there is a condenser at the base of the distributor. It is connected between the +12v feed and the distributor body(ground). But now also that has been bypassed so that might be the problem. There is nothing to filter the spikes. After all coil does create all kinds of noise.

To verify this attached my oscilloscope between the coil ground and +12v. There was typical fluctuation in voltage but also some very fast and high voltage transients. They were so short in duration that my old scope almost could not show them. I circled them in red.



Also when I used my plain multimeter in AC mode and measured, it sometimes showed over 100 volts! That's how massive the spikes are. At this point I opened my spare distributor and took the condenser(capacitor) and just to make sure I soldered another old capacitor I had laying around to it to create some filter for testing. The original condenser reads 3MF, which I think means 3000uf. To verify it the metal cover would need to be opened, but I didn't do that.



Diy filter worked allright, the situation was better and the spikes were now about one fourth what they were and the serial connection worked better but still not even close to perfect.

The next clue to extra noise came, when I had the distributor coil over off when the car was idling and I noticed some small arcing under the coil metal body and between the middle ground strip. That's a no no, so I took off the coil and used sand paper to clean both surfaces to remove the obvious oxidation and improve the contact. That worked right away, the serial connection worked double the better.

At this point I received the new and more high quality 16V 1000uf ultra low ESR & low impedance capacitors I had ordered earlier for this purpose. I figured I would install one to close as possible to the coil to futher maximise filtering effect between ground and 12v. There's very little space under the cover but the cap fit right in.



Well the cap worked pretty good, now the spikes were gone and the multimeter read maximum 0.3V at AC position. Thats quite an improvement, huh?

The serial connection is now 90% good. But for some reason there still is some disturbance. I had earlier connected the scope to the IGBT wire/C- terminal that is to the left of the ground strip. It was far from perfect



Notice the pulsating waveform? I think that's the feedback wave from the coil that I've read about.

Here comes the first question, how would you proceed to make the serial work perfect, should I also create a filter for the IGBT signal?

[VEMS]

Hello Machismo,

Are you using a real serial port or a usb-to-serial converter ?

Best regards, Dave

[Machismo]

Hi,

Real serial. I've been thinking that since the coil ground goes to engine block grounding point, where there are several other grounds as well, so one thing I could try is to change the coil ground to separate point in chassis?

[VEMS]

Hello Machismo,

Real serial thats perfect, usb2serials are known to be quite sensitive to HV noise. With coil ground do you mean the coil secondary side ground ? Than yes it makes sense to ground this near the point of spark (e.g. on the head) separate from the normal GND point.

Its also imperative to check if all grounds on the v3 are connected, its recommended to connect all 5 (1 sensor GND + 4 power GND) and join them in a common (star point) arrangement in single spot.

Best regards, Dave

[Machismo]

Both the primary and secondary coil grounds are connected to the same point right at the coil, so from there on, there is only one ground to connect.

All grounds are connected on the v3 and properly in star point arrangement, so no room for improvement there.

But I wonder what would happen if I connected the coil ground also straight to v3 power ground star point, in addition of the chassis. Is that recommended or a bad idea?

[VEMS]

Hello Machismo,

Both the primary and secondary coil grounds are connected to the same point right at the coil, so from there on, there is only one ground to connect.

If i look at your coil picture (the one with the capacitor applied), i see the coil secondary GND (black middle wire) being connected to the coil transformer ferrite/iron under bolt. This point needs to be be connected to your engine head. The red wire (coil primary+) to the ignition fuse, the yellow wire (coil primary -) going to one of the v3 ignition outputs. Your filtering capacitor needs to connect between red  (coil primary+) and engine ground preferably near coil.

Is this how its is currently wired up ?

Best regards, Dave

[Machismo]

i see the coil secondary GND (black middle wire) being connected to the coil transformer ferrite/iron under bolt. This point needs to be be connected to your engine head.

Well, it was this way from the factory, so that's why I didn't separate it and connect it elsewhere. But on the other hand, it's not a factory configuration anymore so I'll certainly try that.

The red wire (coil primary+) to the ignition fuse, the yellow wire (coil primary -) going to one of the v3 ignition outputs. Your filtering capacitor needs to connect between red  (coil primary+) and engine ground preferably near coil.
Is this how its is currently wired up ?

Yes.

[VEMS]

Hello Machismo

Well, it was this way from the factory, so that's why I didn't separate it and connect it elsewhere. But on the other hand, it's not a factory configuration anymore so I'll certainly try that.

Grounding the ferrite/iron of the coil is fine as long as it is also connected to engine head to close the loop between point of spark and return current to coil secondary.

Best regards, Dave