Faint Spark 2001 Chevy Blazer S10

1991 Chevy S10 BlazerOn my blazer I have changed the crankshaft sensor the ucm and the ignition coil pack. Even went as far as changing the ignition switch in the steering wheel. I am getting a very faint spark from the coil pack and its not starting the truck. What could the problem be?


Weak or Faint Spark

In battery system, weak spark may be due to low battery voltage. Low voltage won’t allow proper magnetic fields to be created across primary and secondary windings of coil. Bad battery contacts, bad ignition switch contacts, faulty connection of any wire in ignition system can also cause weak spark.

Flaw in ignition module may cause weak spark. Best test method to simply replace module with known good module and try to start engine.


On the HEI you have 4 main parts that gives the spark.
  1. The coil (mounted in top of distributor cap)
  2. Under the coil is a carbon bushing with spring on it.. This touchs bottom of coil and sticks through cap and hits the rotor button… Think of this carbon button as your ‘coil wire’
  3. Inside the distributor you ten have the magnetic pickup coil.. The round star looking thing that the shaft sticks up through.. This is the main working part of distributor.
  4. Then you have the ignition module.
A weak spark is normal for 1 of a few things.
  • Your not getting a good full 12 volts to the distributor
  • The coil is going bad
  • The carbon button is worn down too much
  • Or the module is going out..