Wiring up Ignition Systems

My first task was to wire a simple ignition circuit consisting of a coil, spark plug, power supply, and a function generator to trigger the spark.

A simple enough circuit, the hardest part was adjusting the function generator to operate the coil correctly, as it was the first time I had used one. I also had a slight fault in my dwell time pattern, which I could not fully remove, even after replacing a few of the components

The next circuit I built used an ignition module to amplify a trigger signal to the coil. This circuit is alot like the last one I built, except the trigger is amplified by an ignition module, which means a much smaller signal is needed to ignite the spark. To wire this, I first had to find out the pin outs for the ignition module I was using, this particular one being from a Toyota 4a-fe engine. After some research on the always faithful Google, I found a pin out diagram, and also found the reason for the mysterious fifth pin (I already knew the use for the four others, just not which went where). The last pin was for a misfire detection function.

The four pins used on the ignition module consisted of Power Supply +12v, Earth, Trigger signal, and Output to Coil.

Other than figuring out the wiring of the ignition module, this circuit was quite simple to wire up, as it was very similar to the last, and the function generator was already calibrated.

The next circuit to build used a distributor to send a signal to the ignition module. The circuit was wired up alot like the last, but with a distributor in place of the function generator. Spinning the distributor rotor creates a signal much like that of the function generator, causing the spark to fire as each tooth of the rotor passes the pick up.

 The third circuit I built was for a wasted spark ignition system. For this circuit, I used the function generator, and the same ignition module, but instead of the single plug coil, I used a wasted spark coil pack, with two leads and spark plugs. The wiring was much the same as the other circuits, except for the fact that there were two seperate spark plugs firing off the one coil. This is achieved by grounding one of the spark plugs through the other plug, and then back into the coil, to create a full circuit. The property of electricity that it naturally wants to return to its source, makes this possible. 

 Below is a simple diagram showing the internal functions of a wasted spark coil for a 6 cylinder vehicle.

On this coil, there is one 12v supply pin, but in others there may be one for each coil. It shows how two cylinders are triggered at the same time, and subsequently fire at the same time also. This is the reason for the name 'Wasted Spark', as one spark is always fired on the exhaust stroke.

The next circuit I built contained a Coil Over Plug setup, which contains a coil and built-in ignitor in one unit (see below), removing the need for a seperate ignitor. These units will run one coil for each cylinder, making them very efficient, and less likely to fail. A bad point is that the are difficult to test, as there is no access to the coil primary.

This circuit did not require an ignitor as the coil incorporated an ignitor inside of it. This meant that i wired it straight to the function generator to complete the circuit. Once wired up, i tested it's operation and it seemed to work well.

Testing Ignition Coils

First task we had was to obtain two different ignition coils, and test them against specification. We hadto determine the part numbers, and search the spec sheets on google. Once that was completed, we set to testing.

My two coils were:

C6R-500
&
CTI-118

My test results were as follows:

C6R-500
Operating Voltage: 12v
Primary Resistance Specification: 1.20 - 1.50 ohms
Actual Primary Resistance: 1.3ohms
Secondary Resistance Specification: 6.5K - 8.5K ohms
Actual Secondary Resistance: 8K ohms
Earth leakage: OL

CTI-118
Operating Voltage: 12v
Primary Resistance Specification: 1.0 - 1.3 ohms
Actual Primary Resistance: 1.2ohms
Secondary Resistance Specification: 8.5K - 9.5K ohms
Actual Secondary Resistance: 9.33K ohms
Earth Leakage: OL

Both coils were in good condition and 100% serviceable.
If resistances were above specification, this may be caused by a break in the windings, and could result in incorrect charging and misfire.
If they were below specification, it may cause over heating and damge to other components.

My next task was to test a wasted spark coil.

I used a 6 output Coil from a Series 1 Holden Commodore 3.8l V6 89-90.
Part No: TIC032

I tested each of the three coils separately.

My results were as follows:

Coil 1 Primary: 1.2ohms
Coil 2 Primary: 1.2ohms
Coil 3 Primary: 1.1ohms

Coil 1 Secondary: 12.67K ohms
Coil 2 Secondary: 12.73K ohms
Coil 3 Secondary: 12.75K ohms

This coil pack was completely serviceable, as all of my reading came within, or near specification.

If either resistance was low, especially the secondary, it could mean there is a short circuit in the windings, and the coil will not operate correctly, if at all. If resistance was high, for example, OL, this could mean there is an open circuit in the windings, and the coil will not operate at all.

The next test was on Ballast resistors. I used two different Ballast resistors for my test.

Part No. BR1 and Part No. BR3. 

I had to obtain the resistance specification for each. These I found on a specification sheet stored with the resistors.

Specs were:

BR1 = .9 - 1.1ohm

BR3 = 1.5 - 1.7ohm

My readings were: 

BR1 = .7ohm

BR3 = 2ohm

Neither of these Ballast resistors were serviceable, as each was outside of their proper specification. Lower resistance may cause overheating of the coil and damage to the ignition components, while higher resistance may cause improper charging of coil and may lead to misfire, especially at higher RPM's

Injector testing

This section includes injector testing, and also injector cleaning.
First up, we did electrical testing. We found four injectors, and tested their resistance according to the specification of each. We also tested earth leakage to the shell of the injector. Before this was done though, we hadto check the internal resistance of the multimeter used, and then subtract that from our total reading. On each of my four injectors, my resistance readings were within spec, and none of them had any earth leakage.

My readings were as follows:

       Injector 1: 13.9
              Spec: 13.9
Earth Leakage: OL

       Injector 2: 13.9
              Spec: 13.8
Earth Leakage: OL

       Injector 3: 13.8
              Spec: 13.8
Earth Leakage: OL

       Injector 4: 13.9
              Spec: 13.8
Earth Leakage: OL

If these readings were not within specification, they may cause incorrect opening/closing, or may cause them not to operate at all.

After these were completed i began bench testing the injectors on specialist equipment used for testing/cleaning injectors.
I tested leakage and flow on each of my four injectors. For flow, i hadto test over 15 seconds, and then multiply that figure by four to get my reading. I hadto do this as if i had simply run the test over a minute, the test tube would have overflowed.

My readings are as follows:

Injector 1: Flow = 190cc
                Leakage = 0DPM (Drips Per Minute)

Injector 2: Flow = 190cc
                Leakage = 0DPM

Injector 3: Flow = 190cc
                Leakage = 0DPM

Injector 4: Flow = 190cc
                Leakage = 0DPM

On the earth leakage test, pressure is held behind injectors with them closed, and leakage is observed and determined over a minute.

If flow is below specification, the injector may cause its cylinder to run lean, and cause a lack of performance/fuel economy. If leakage is present, it will cause unwanted drips while engine is inactive, and cause fuel build-ups in the runners of the engine.