Homemade COP Coil Bench Tester

Dec. 1, 2016
A love for tinkering and creating tools helped pave the way for a homemade coil bench tester

What It Is: Coil bench tester designed to bench test almost any two-wire ignition coil or coil-on-plug unit. 

The Inspiration: About 15 years ago, Chris Hopkins noticed a lot of Ford vehicles were coming into the shop with faulty ignition systems. Back then, using fancy sensors or scanners wasn’t an option, so determining the faulty coil was a challenge. Hopkins needed to find a solution. He shopped around and found a couple of products that would allow him to test coils without running the vehicle, but they were in the $300–$400 range. Hopkins has always enjoyed tinkering, so he decided to make his own.  

What It Does: The coil tester combines an ignition module and a square wave generator. The ignition module has the ability to turn the coil on and off, which allows the user to drive coils without being connected to the car.  In order to use it, the coil is taken off the car and connected to Hopkins’ homemade device and to an adjustable gap spark tester (Hopkins suggests a Thexton 458).  When the switch is pressed, the square wave generator creates a 0-12 V signal that triggers the module on and off continuously, which causes the coil to produce a spark. Based on the size of the gap that the spark can travel, the user can determine whether or not the coil is weak. The coil bench tester is a time saver when a vehicle needs to be taken apart, making it difficult or impossible to run the engine. The device can also be used to test a new coil before it is installed. 

How It’s Made: The coil tester combines an ignition module and a square wave generator. The two separate devices allow the user to power two drive coils without being connected to the car. The ignition module and square wave generator are connected, and the coil be tested is added to complete the electrical circuit. 

The power from the battery on the bench runs through a switch to supply the signal generator, module and the ignition coil. The power leads have alligator clamps to grap the battery posts and the coil leads have banana jacks on them, which allows the user to use different connectors for various types of coils. 

Cost: $60–$80.

ROI: Hopkins says the amount he uses the device varies on the types of vehicles and jobs that come in. It could be twice per week or it could be a few weeks before he uses it. Hopkins says that the coil tester paid for itself within a couple of uses and creating it himself instead of purchasing one saved him a few hundred dollars. 

“If I’m working on a Ford V8, it’ll save me 30 minutes,” Hopkins says. “I can test each coil within a minute or two, and it also allows me to test coils that would not have been possible if I couldn’t run the car.”

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