How To Find A Misfiring Cylinder (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

How To Find A Misfiring Cylinder (1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup, And GMC Sonoma)

Even though the 2.8L V6 TBI fuel injected Chevy S10 pickup (GMC S15 pickup, GMC Sonoma) does not come with OBD II misfire diagnostics, you can still find out exactly which cylinder is dead (misfiring)! In this tutorial, I'll show you how to do that in a step-by-step way.

From personal experience, I can tell you that it's not that hard. It involves doing a very simple manual cylinder balance test.

In Spanish You can find this tutorial in Spanish here: Cómo Diagnósticar Una Falla En Cilindro (2.8L V6 GM) (at:

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.

This tutorial also applies to the 2.8L Chevy S10 Blazer, 2.8L GMC S15 Jimmy. See the 'Applies To' box on the left column (desktop) or at the bottom of the page (mobile device) for more info.

The 3 Basic Causes Of A Misfiring (Dead) Cylinder

Every cylinder in your 2.8L v6 GM engine needs fuel, air (compression), and spark to be able to produce power. It's when one of these is missing from the cylinder that that cylinder misfires. I'm going to be referring to the misfiring cylinder as a dead cylinder throughout the tutorial

The components that are usually behind most cylinder misfires are:

  1. Bad spark plug wires.
    • They usually don't fail all at once. For the most part, you'll have one or two spark plug wires that simply stop transmitting the spark from the coil pack to the spark plug.
  2. Bad distributor cap.
    • You have one of the distributor cap towers not transmitting spark. The end result is a cylinder that is not getting spark does a cylinder misfire.
  3. Bad spark plug.
    • Spark plugs don't last forever and are gonna' wear out eventually. What aggravates the problem is if the engine in your car or mini-van is burning oil. If this is the case, one or several spark plugs become carbon fouled and the air gap (between the center electrode and the side electrode) closes. This results in a no-spark condition for that or those specific cylinders.
  4. Low or no compression in one or several cylinders.
    • Engine compression problems due to worn out / burned valves or worn out compression rings are another common cause of a misfire. Will cause the cylinder to misfire!

You'll notice that I did not include fuel injector problems in the list above. This is due to the fact that a fuel injector causing a specific cylinder to misfire is extremely rare in this type of throttle body fuel injection system.

TEST 1: Doing A Manual Cylinder Balance Test

The key to finding the dead (misfiring) cylinder is to do a manual cylinder balance test. It sounds complicated, but it's a pretty easy test to do.

In a nutshell: a small piece of vacuum hose is placed between a distributor cap tower and the spark plug wire that connects to it (the arrow in the photo above points to this small vacuum hose). Then using a 12 volt automotive test light, the spark plug wire is shorted by touching the vacuum hose with the metal pointy end of the 12 Volt automotive test light.

If the cylinder is dead to begin with, then the engine's idle will not be affected. In other words, since the cylinder is already dead, shorting out its spark plug wire will not cause the engine to shake more. But if the cylinder is 'alive', then shorting out its spark plug wire will make the engine idle rough (the engine will shake more).

These are the test steps:

  1. 1

    Cut 2 small pieces of vacuum hose about 1.25 inches long (no longer).

    Make a small 30 degree cut on one end. This end is going to be inserted in the spark plug wire's metal terminal (inside it's rubber boot).

  2. 2

    Disconnect spark plug wire #1 and #2 from the distributor cap. You can identify these 2 wires from the illustration below.

  3. 3

    Insert the vacuum hose into the spark plug wire's metal terminal (inside its rubber boot), then connect this spark plug wire (with the vacuum hose) back onto the distributor cap.

    Repeat the above on the other spark plug wire.

  4. 4

    Crank and start the engine once you have both spark plug wires with the piece of vacuum hose between the towers.

    If the vacuum hoses are inserted correctly, the spark will be channeled across the vacuum hose and into the spark plug wire.

  5. 5

    As the engine idles, 'short out' the spark plug wire by touching the vacuum hose with the 12 Volt test light (see the photo above).

    NOTE: The 12 Volt test light has to be Grounded, preferably directly on the battery negative (-) terminal.

    This will channel the spark thru' the test light (don't worry, it's very safe) and effectively kill the cylinder. If the cylinder is dead to begin with, shorting the spark plug wire WILL HAVE NO EFFECT on engine idle. If the cylinder is NOT dead, then this will have a negative effect on engine idle since it will get worse.

  6. 6

    Repeat this test step on the remaining 4 spark plug wires.

Let's take a look at what your test results mean

CASE 1: One or more cylinders are dead. This tells you that that cylinder is dead. It's dead because it is either missing spark or it is missing compression. Your next step is to go to: TEST 2: Checking The Spark Plug Wire.

CASE 2: All cylinders are alive. This tells you that all of the six cylinders are getting spark, fuel, and have compression.

Now if the engines idle is still rough, meaning that the engine shakes too much in idle, then you've a condition that's affecting all cylinders. Vacuum leaks, low fuel pressure, uneven compression across all 6 cylinders.

TEST 2: Checking The Spark Plug Wire

Checking The Spark Plug Wire. How To Find A Misfiring Cylinder (1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup, And GMC Sonoma)

If you've reached this point, then in TEST 1 you found one or more cylinders that are dead (misfiring). Now we can begin to start finding out what is behind the misfire.

As mentioned earlier, the most common cause of a misfire is a lack of spark. So in this test section, we're gonna' make sure that the spark plug wire is transmitting spark to the dead cylinder.

This is a pretty easy to do. You'll need a spark tester to accomplish it. I recommend using an HEI spark tester. If you don't have one, you can find out more about it here and also where to buy it: The HEI Spark Tester (The Best Spark Tester On The Market).

OK, these are the test steps:

  1. 1

    Disconnect the vacuum hoses from the distributor cap and reattach the spark plug wires to the distributor cap.

  2. 2

    Locate the spark plug wire of the dead cylinder and disconnect it from its spark plug.

    IMPORTANT: Use a spark plug wire wrench to disconnect the spark plug wire from the spark plug. You can find out more about it here: How To Use A Spark Plug Wire Puller And Where To Buy One

  3. 3

    Attach the HEI spark tester to the dead cylinder's spark plug wire.

  4. 4

    Connect the HEI spark tester directly on the battery negative (-) post using a jump start cable.

  5. 5

    Have a helper crank the engine once the spark tester is set up. Your job now is to observe the spark tester from a safe distance.

  6. 6

    You'll get one of two results:

    1.) Spark.

    2.) No spark.

Let's take a look at what your test results mean

CASE 1: The HEI spark tester sparked. This test result tells you that the dead cylinder is getting spark. Your next step now is to go to check the spark plug and compression of that dead cylinder.

For this test go to: TEST 3: Checking The Cylinder's Compression.

CASE 2: The HEI spark tester DID NOT spark. This test result tells you that the cylinder is dead due to a lack of spark. This test result also tells you that either the spark plug wire or the distributor cap tower (that this wire connects to) is bad.

Thankfully, we can find out which of the two it is without having to run out and buy both the distributor cap and the spark plug wires. So, your next step is to go on to: TEST 4: Testing The Distributor Cap.

Chevrolet Vehicles:

  • S10 Blazer 2.8L
    • 1988, 1989
  • S10 Pickup 2.8L
    • 1988, 1989, 1990, 1991 1992, 1993

GMC Vehicle:

  • S15 Jimmy 2.8L
    • 1986, 1987, 1988, 1989
  • S15 Pickup 2.8L
    • 1986, 1987, 1988, 1989, 1990
  • Sonoma 2.8L
    • 1991, 1992, 1993