If the ignition coil on your 2.8L Chevy S10 (GMC S15) fails, the engine is going to crank but not start due to a lack of spark.
The cool thing is that testing the ignition coil is not that hard. You're going to be surprised just how easy it is to find out.
In this tutorial, I'll show you how to test it in a step-by-step way without having to take it off the engine and without any expensive diagnostic test equipment.
Contents of this tutorial at a glance:
- Symptoms Of A Bad Ignition Coil.
- Ignition Coil Connector Circuit Descriptions.
- How The Ignition Coil Works.
- Where To Buy The Ignition Coil And Save.
- TEST 1: Checking The Ignition Coil High Tension Wire For Spark.
- TEST 2: Testing For Spark Directly On The Coil Tower.
- TEST 3: Making Sure The Ignition Coil Is Getting 12 Volts.
- TEST 4: Making Sure The Ignition Coil Is Getting the Activation Signal.
- More 2.8L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials.
You can find this tutorial in Spanish here: Cómo Probar La Bobina De Encendido (2.8L V6 GM) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.8L Chevrolet S10 Pickup: 1988, 1989, 1990, 1991, 1992, 1993.
- 2.8L GMC S15 Pickup: 1988, 1989, 1990.
- 2.8L GMC Sonoma: 1991, 1992, 1993.
NOTE: This tutorial complements the tutorial on how to test the ignition control module (ICM). You can find the ICM test tutorial here: How To Test The Ignition Control Module (2.8L V6 GM).
Symptoms Of A Bad Ignition Coil
The most obvious symptoms of a bad ignition coil is that your 2.8L V6 Chevy S10 (GMC S15) is not gonna start. To be a bit more specific, the engine will turn over but won't start.
This is due to the fact that the ignition coil is the component tasked with the job of creating and delivering spark to the ignition distributor. If the distributor isn't getting spark, none of the 6 cylinders will either.
Here are some more specific symptoms you'll see:
- Engine cranks but does not start.
- Both fuel injectors will be injecting fuel.
- Fuel pump is working.
Ignition Coil Connector Circuit Descriptions
| GREY CONNECTOR | ||
|---|---|---|
| Terminal | Wire | Description |
| A | White (WHT) | Tach signal output |
| B | Pink (PNK) | 12 Volts (input from ignition switch) |
| BLACK CONNECTOR | ||
|---|---|---|
| Terminal | Wire | Description |
| C | White (WHT) | IC control signal |
| D | Pink (PNK) | 12 Volts (output to ICM) |
How The Ignition Coil Works
The ignition coil on the 2.8L V6 Chevy S10 pickup (GMC S15 pickup, GMC Sonoma) has 4 wires coming out of its connector, but operates on 12 Volts and Ground.
In this section, I'll explain how it creates a spark. This info will help you understand what we'll be testing in the upcoming tutorial pages.
When you turn the key to start the engine, this is the process that occurs:
- The ignition coil receives 12 Volts through the pink (PNK) wire of the gray connector; which I've labeled with the letter B in the image above.
- The 12 Volts then leave the ignition coil through the pink (PNK) wire of the black connector (marked with the letter D).
- These 12 Volts are sent to the ignition control module to power it.
- When the engine starts to crank, the pickup coil (which acts as the crankshaft position sensor) begins sending its position signals to the ignition control module.
- The ignition control module activates the ignition coil through the white wire of the black connector (marked with the letter C).
- The ignition control module causes the ignition coil to spark by turning the Ground circuit ON and OFF.
The cool thing is that we can determine if the ignition coil is functioning properly by checking if it's receiving 12 Volts and an activation signal.
To further help your ignition coil troubleshooting efforts, you can find the ignition system circuit diagram here: 1991-1993 2.8L Chevy S10 Ignition System Circuit Diagram.
Where To Buy The Ignition Coil And Save
If you find that you do have a defective ignition coil, the following links will help you to comparison shop for the ignition coil on your S10:
Not sure if the above ignition coil fits your particular S10 (S15)? Don't worry, once you click on the links and arrive on the site, they'll make sure it fits! If it doesn't, they'll find you the right one.
TEST 1: Checking The Ignition Coil High Tension Wire For Spark
OK, to get this show on the road we'll start by testing the ignition coil's high tension wire for spark.
This spark test will let us know right away whether or not the distributor cap is receiving any spark to distribute to the spark plugs.
A bad ignition coil high tension wire that doesn't transfer spark from the ignition coil to the distributor cap is a common issue in this type of ignition system.
To perform the spark test, I recommend using the HEI spark tester, as it's highly accurate and inexpensive. For more information and to purchase this spark tester, you can follow this link: The HEI Spark Tester (The Best Spark Tester On The Market).
NOTE: Disconnect the two throttle body fuel injectors before starting all the tests in this tutorial.
Alright, these are the test steps:
- 1
Disconnect the high tension wire from the center tower of the distributor cap.
NOTE: Leave the other end of the high tension wire attached to the ignition coil. - 2
Attach the HEI spark tester to the spark plug cable.
- 3
Connect the spark tester to the battery negative (-) terminal using a battery jump start cable (see the photo above).
- 4
Have your helper crank the engine when you have the spark tester set up.
CAUTION: Observe the spark tester from a safe distance as the engine is being cranked. - 5
The spark tester will give you one of two results: Spark or NO spark.
Let's take a look at what your test results mean:
CASE 1: The spark tester sparked. This test result tells you that the ignition coil and its high tension wire are OK.
Based on the results of your test, you can conclude that the ignition coil and its high tension wire are functioning properly and not the cause of the no-start problem in your 2.8L V6 S10/S15.
CASE 2: You got a no spark test result. This test result definitely tells you that a no-spark condition is behind your S10's engine not starting.
The next step is to go to: TEST 2: Testing For Spark Directly On The Coil Tower.
