Evening!
Without throwing at you single things to do , i'll write what i do to troubleshoot a problem with the car's ignition. Others to do with internals of the engine may have to be diagnosed further by yourself. I hope this helps, as it has always worked for me many times in the past 
Step 1 - Battery
(N.B. When checking Amps, make sure you measure on the highest setting first, and descend, just incase too many Amps are draw through the circuit, e.g. setting max=20A, and 35A is drawn through).
(N.B. Set the multimeter to DC amps when mearsure current, as this is what a car's wiring sytem uses!!)
Voltage
- With a multimeter, check to see what the potential difference (Voltage) is from both the positive and negative terminals on the battery. Make sure that it is switched to VOLTAGE, not any application of AMPS, as i guarantee that your multimeter with spark, and will not work anymore (i.e. fried the thing to death!).
- The multimeter probes can be either negative-to-negative and positive-to-positive, or the opposite from each, the only difference is that the opposite combination will produce a negative reading on your multimeter, which is not a problem.
- A fully operational and charged battery will have a p.d. of roughly 12.6v. 12.3v is half battery power, and will result in less cranking power.
Cranking Amps
- From DIY you wont necessarily know the definite Amp draw, as you'll probably have to go and get it tested with a sufficiently rated Ammeter. What I mean is, is that cells within the battery could be faulty, meaning that the same Voltage is seen due to the circuit being in series, but the amount of current passing through can be restricted.
- Now to check for a sufficient Amp draw, you will want to check to see how much the Voltage drops when cranking the engine.
- If you have any internal light door switches (i.e. automatically turn on when door opens), remove the multimeter first, and then cover them up, so that no current is drawn through the multimeter.
- Set the multimeter back up as it was before, and stick it face down on the rear window (or in hands if long enough), and turn the engine over.
- If the voltage drops down to about 4/5V, not enough Amps are being drawn through the battery, therefore the starter isn't getting enough power to turn the engine over fast enough. What you want to see is around 10V+, indicating the battery is in a good working order.
'Parasitic' Drain - (Not necessarily anything to do with your problem)
- This wont really affect a fully charged (and properly working) battery, but can be an indication as to whether the battery runs down without anything switched on. Reasons for having anything on constantly is going to be for a radio code, or ECU memory, but the ECU problem wont affect you!
- Connect the multimeter negative probe to the battery earth terminal, and the positive probe to the connector of the earth lead, and check the Amp draw.
- If you do have a radio, then you will see a range of about 1-3 milliamps (0.001-0.003A). This is incredibly small, and will have no effect on the problems your are describing, but it is good to know.
- If it is something like 0.5A, 3A or even higher, then you definitely have a current draw, and you will need to find 'common areas' within your whole wiring system (switches) that should be off, but power is still being put through.
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- If all these check out ok, and your starter motor is not turning over fast enough, there may be a problem with the starter moter solenoid, the starter motor itself, or the wiring within/leading up to them both.
Step 2 - Engine Ancillaries
Ignition Coil
An ignition coil------> First, to create an output charge means the secondary coil in your coil pack (negative terminal) is putting out a current. A coil works by having 2 separate coils wound around an iron core. The secondary coil will most likely have about 500 times more windings than the primary coil (positive terminal) so more current can be conducted than what is given. When power is put through the primary windings, an electromagnetic field is created. The secondary windings will then conduct a Voltage because of electromagnetism. As this power is going through the primary, much more power wanting to go throught the secondary coil, but it cant because of the very very high resistance (0.0024 Amps flowing does jack sh*t!). It's just connected in parallel with the primary coil so that the wire doesn't get damaged. When the circuit breakers open, this current from the electromagnetism is let through the coil tower at around 15,000 Volts, and through the spark plugs as another way of earthing. The spark arcs across the arm and terminal of the spark plugs, and ignites the fuel due to the intense amount of heat energy that is emitted.
You can also have a standard 12v coil, and a 9v ballasted coil. The ballasted coil is where you have a ballast resistor in between the primary input voltage terminal on the coil, and the power source. The resistor is bypassed during starting, so the intial, full voltage supply is there to help get the engine running, but is live when running . This means the system only uses 9v (all that is needed) when normally running.
- With a spark plug out of cylinder head, and connected to an HT lead, make sure that the correct spark plug arm and terminal gap is present. You want to be looking for about 25 thou (0.025 inches) or about 0.6mm.
- Postition the spark plug so that any metal part (i.e. thread) is touching anything that is metal and grounded. You may want to hold it in position with an insulated screwdriver to both get a good earth, and to not shock yourself.
- Crank the engine, and you should see pulsing sparks. This spark should be a bright blue, indication sufficient power is being provided to ignite the fuel. If it is of an orange based colour, then not enough energy is being produced by the secondary coil within the coil pack. This can mean 1 of 2 things. First, the coil is faulty, described otherwise to what is said below. Second, your distributor system is faulty.
- Repeat for each spark plug.
- Also, you want to test the resistance of the coil windings. This is becasue you have the same alternator Voltage when the car is running, so if the resistance is incorrect, then the Amps that can go through the coil will be affected; use the equation V=I*R or Voltage (Volts) = Current (Amps) * Resistance (Ohms) if you need to, but not necessary.
- Switch your multimeter to Ohms, put the positive probe on the positive terminal of the coil, and the negative probe on the negative terminal. This is testing the primary winding resistance, and you should see a reading of 0.4 - 2 ohms. Now, keep the positive probe on the positive terminal, but move the negative probe to the coil tower. This is testing the secondary winding resistance, and you should see a reading (or no reading at all!) 6,000 - 15,000 ohms.
Distributor System
- Remove the distributor cap, and check the gap distance is between the contact breakers. You may have to crank the engine a few times (without removing distributor) to get the breaker open.
- The correct gap should be around 15 thou (0.015 inches). If not, correct it to this setting.
- Give a visual inspection as to whether anything is broken, or shouldnt be there (or what should be there!).
- Its a very unlikely cirumstance to replace the actual distributor, do to the parts that matter are connected to its shaft, and operate separately/individually.
- You can also check for continuity between the distributor cap contacts and the coil tower to HT lead connection.
Alternator - Will need to be jump started for this if can start independantly.
- Connect the multimeter to the battery like described when checking the voltage with the engine running.
- You should have a reading of about 13.5v, rather than 12.6v. This is becasue rather than the battery powering the car and still sending power the battery via the 'exciter' wire (for starting the alternator to produce a current when starting), the alternator is instead there to power everything, and to charge the battery. Other wise you could have a flat battery and working alternator to power the car, but cant start the car again when the engine isnt running (the battery is only there to power the car to start and for unswitched circuits - like lights).
- The alternator should give out around 13.5v to power the battery (indirectly); the current is drawn from the battery like a capacitor so electrical applications dont pulse from the AC/DC conversion (if they were to be directly powered from the alternator).
- If the reading is EQUAL to or LESS than the voltage from the battery, the alternator may be faulty, or the alternator belt may be incorrectly adjusted. If it is adjusted correctly (rough guide is just not being able to fit socket onto the tightening bracket bolt at a tangent), then the alternator may be bad, like its diode pack not working (a diode pack is there to convert the AC currenct produced within the alternator, to DC, as diodes only let current flow through one way.), and the car's wiring system uses DC.
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I do not think there is a problem with the carb/fuelling due to the fact it still runs when jumped, but i can be wrong!
I know there aren't any relay problems due to the fact everything is getting a current and operating.
This is all i can think of atm, this is just covering the ignition, which like you described, is the probable cause of this mess!
I hope it helps, oh and sorry for over explanation, i don't know how much you know as far as circuitry, so i gave you the whole lot
Kind regards
Ashley
Edited by SpeedDemon, 24 January 2015 - 11:53 PM.
went and corrected the stupid mistakes xD (i.e. alternator voltage, coil not coil pack, 0.25 plug gap, ballast resistor ect ...)
