GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1996 🢒 Chevy Suburban - 4WD 🢒 Engine 🢒 Engine Electrical 🢒 Spark Plug Visual Diagnosis

Step

Action

Value(s)

Yes

No

1
  1. Remove the spark plug from the engine.
  2. Note which cylinder the plug is from.

Do you see a brown to grayish tan deposit with a slight electrode wear?

--

Go to Step 2

Go to Step 3

2
  1. This is normal wear.
  2. Clean, regap and reinstall the plug.
  3. Tighten the plug.

Is the repair complete?

--

System OK

--

3

Do you see dry, fluffy, black carbon deposits?

--

Go to Step 4

Go to Step 5

4
  1. This indicates poor ignition output.
  2. Check distributor to coil connections.
  3. Correct all connections, if necessary.

Is the repair complete?

--

System OK

--

5

Do you see wet, oily deposits with very little electrode wear?

--

Go to Step 6

Go to Step 7

6
  1. This may result from:
    2. • "Break-in" of a new or recently overhauled engine
    • Excessive valve stem guide clearances
    • Worn intake valve seals
  2. Degrease, gap and reinstall the spark plugs.

Is the repair complete?

--

System OK

--

7

Do you see red, brown, yellow and/or white colored coatings on the insulator?

--

Go to Step 8

Go to Step 9

8
  1. These are the by-products of combustion.
  2. Clean, regap, and reinstall the spark plugs.
  3. Replace the spark plugs, if the insulator is heavily coated.

Is the repair complete?

--

System OK

--

9

Are there heavy deposits of dark colored coatings, especially on the side of the plug facing the intake valve?

--

Go to Step 10

Go to Step 11

10
  1. This is the result of leaking valve seals.
  2. Check the valve seals.
  3. Replace valve seals if necessary.
  4. Clean, regap, and reinstall the spark plugs.

Is the repair complete?

--

System OK

--

11

Is there a shiny, yellow glaze coating on the spark plug insulator?

--

Go to Step 12

Go to Step 13

12
  1. These are the melted by-products of combustion.
  2. Avoid wide open throttle after long periods of low speed operation.
  3. Replace the spark plugs.

Is the repair complete?

--

System OK

--

13

Are the insulator tips blistered or burned and the electrodes are badly eroded?

--

Go to Step 14

Go to Step 15

14
  1. This is the result of overheating.
  2. Check the spark plug heat range.
  3. Replace the spark plugs if heat range is incorrect.

Is the repair complete?

--

System OK

--

15

Are the insulator tips broken or cracked?

--

Go to Step 16

System OK

16

Replace the spark plugs.

Is the repair complete?

--

System OK

--