How to Tell If You Have a Faulty Distributor

July 2, 2012

A faulty engine distributor won't spark, which will either prevent the engine from starting or cause it a running engine to fail.

Engine Distributor

In order for the ignition system to work properly it is important to keep the engine distributor operating at maximum efficiency. The distributor also disburses current to the spark plugs initiating engine performance.

Check the Distributer Cap
Often the distributor cap is suspect. The distributor cap should be inspected carefully to see how the sparks are arcing. The internal and external surface of the cap should be clean. No erosion should be on the surface and the firing points should be free of rust or corrosion. The rotor should be checked as well, this is the point where high-tension spark moves from one distributor cap terminal to another and it must be in pristine condition. This needs to be checked for burns, traces of carbon and should have a secure fit.

Sometimes, the issue is a slight buildup of carbon inside the distributor. This carbon trace can conduct electricity that affects performance. It could short out the coil voltage and cause a faulty connection inside the terminal of the distributor cap. The result is a misfire in the spark plugs. Look for any cracks or carbon trace in the cap.

Check the Contact Points
Inspect the condenser; the engine will not function if it is broken. The current will short out if the electrical connection is grounded. If the condenser is open, it is due to a broken wire lead. This causes point arcing and burn, which will stall out the engine.

Take a look at the contact points. If points are bad, the engine could experience multiple problems. Bad point connections cause engine overrun, timing issues, speed missing and causes the engine to misfire or fail to start. Look closely at the surface of contact points. Check for corrosion or degradation. If the points look burned or the contacts have eroded or a worn out block, these parts need replacing.

Check the Arc
Pull a plug wire off the distributor test each one. A screwdriver can be used to check the arc when the ignition is turned. Put the metal part of a screwdriver against the metal of the plug wire. Place the metal screwdriver near the electrode of the distributor. It should not touch the electrode. Step away from the hood and have someone watch the arc while the ignition is turned on. If there is an arc, it is firing. Replace the wire on the distributor electrode after it is checked. Each wire can be checked in this way to expose a misfire or faulty connection in the distributor.

Distributor Replacement

This repair should be simple enough for most car enthusiasts and individuals with some knowledge of car repair.

Tools and Materials

  • White out
  • A rebuilt or new distributor
  • A flathead screwdriver
  • Points
  • A point gap tool
  • A socket wrench
  • A ¼" hex socket

Crank the Engine
Before removing the distributor, crank the engine to get the timing mark on the crank pulley to its top dead center (TDC) mark. This will be visible when you locate the crank pulley, depending on what type of car you have. Consult the owner's manual or a repair manual for the schematic relative to your car.

If the engine of your car is grimy, use white out or nail polish to mark the TDC position on the crank pulley.

Remove the Old Distributor
Remove the clamps holding the distributor in place with a screwdriver. Look at the old distributor in comparison to the new or rebuilt one, to make sure that they match up. They should be the same length, have the same number of gear teeth and be identical. If they are not, return the replacement distributor to the store or retailer and get the correct replacement.

Set the Point Gap
Replace the point piece on the top of the distributor and set the gap in order to ensure the proper firing gap. A point gap tool, which is used to set the gap on the spark plugs, will do this for you. Set the point in a vice or on a flat surface in order to set the spacing. Place the point into the distributor.

Set the Distributor
Place the replacement distributor in the hole where the old one was removed. Slowly lower it into position until you can feel the gears touch the camshaft gears. Rotate the oil pump drive shaft to ensure that the distributor is in its proper position. This is important (and the reason you marked the TDC) because the engine will not fire if the distributor is out of position. Use a screwdriver or ¼" socket for a hex screw slot and slowly rotate the distributor until it matches position.

Take your time and make sure that the positions match up with those of the old distributor.

Fire the Engine
Once you set the distributor and are confident that the timing marks line up, place the clamps back on, replace the distributor cap and fire the engine. Listen for how the engine fires and make sure that there are no hesitations or misses when it starts. If everything sounds fine, you have successfully completed the replacement of the engine distributor.

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