Twice now when I have been working on the car the engine has suddenly died and refused to restart, on both occasions it was down to the points closing up - I finally figured out why. On cars of this age it is normal to have ignition points - basically a switch operated by a cam that switches the ignition coil when it's time to spark. The coil converts the pulsing 12 volt signal in to a 32,000 volt spark, best keep your fingers clear. Anyway the coil takes a lot of current, which is ok when it's pulsing but if the ignition is left on and the points are closed you have big current going through them and they don't like it. The trick is that when the car is cranking and you need the strongest spark the battery voltage is at it's lowest and therefore the spark is at it's weakest. What used to be general practice was to run the coil through a resistor that got shorted out when cranking so the coil gets maximum available voltage at start up and then the voltage falls to about half when running. My coil had a resistor with it but I had bypassed it because when I originally tried setting it up I can't getting a decent spark at cranking.
Fixing it was easy, a relay fired from the signal that goes to the starter solenoid, two wires that go each side of the resistor, they close when the starter is energised and open once the car is running. The resistor is in series with the live side of the ignition coil so the coil always gets about 9 volts whether cranking or running. It works perfectly, thought it was worth mentioning although I am rather tempted to go with electronic ignition if one comes up, points will wear and will need adjusting, an electronic system won't. It's a budget build and it will never do many miles so we will have to see what turns up at the auto jumbles.
Add comment
Comments