How To Test The EGR Valve (1994-1995 2.2L Chevrolet S10, GMC Sonoma)

TEST 2: Applying Vacuum To The EGR Valve

The focus of this test section is to test the EGR valve while we apply/release vacuum to it (with a vacuum pump).

If the EGR valve is OK, you'll notice two things when you apply vacuum to it:

• The EGR valve's pintle should rise (causing the EGR valve to open and let exhaust gas recirculate into the intake manifold).
• The engine's idle should worsen.

If the EGR valve is bad, applying vacuum to it will not affect the EGR valve's pintle and/or the engine's idle.

NOTE: You'll need a vacuum pump to perform this test. If you don't have one, you can run to your local auto parts store (AutoZone, O'Reilly Auto Parts) and borrow one from them. If you'd like to buy a vacuum pump, I recommend the Actron CP7835 Vacuum Pump.

Let's get started:

1. 1

   Disconnect the vacuum line from the EGR valve.

2. 2

   Connect your vacuum pump to the EGR valve.

3. 3

   Start the engine and let it idle.

4. 4

   Apply vacuum to the EGR valve as you observe the engine's idle and the EGR valve's pintle (see image 2 of 2).

5. 5

   The engine's idle should get very rough and the EGR valve's pintle should rise.

6. 6

   Release the vacuum you applied to the EGR valve.

7. 7

   The engine's idle should return to normal and the EGR valve's pintle should lower (to the position it was in step 3).

Let's interpret your test result:

CASE 1: The engine's smooth idle became rough, and the pintle rose when you applied vacuum to the EGR valve. This is the correct test result.

This test result confirms several important things:

• The EGR valve is functioning correctly.
• The EGR passages in the valve's adapter block are open (not blocked with carbon).
• The EGR passages in the cylinder head and intake manifold are open (not blocked with carbon).

If an EGR valve diagnostic trouble code is illuminating the check engine light, the most likely cause is:

• The EGR valve system vacuum hoses are misrouted or broken.
• The EGR valve vacuum solenoid is bad.

CASE 2: The engine's idle was rough to begin with and became rougher, and the pintle rose when you applied vacuum to the EGR valve. This test result usually indicates the EGR valve is stuck open.

Your next test step is to go to: TEST 4: Making Sure The EGR Valve Pintle Is Not Stuck Open.

CASE 3: The engine's smooth idle DID NOT become rough, and the pintle DID NOT rise when you applied vacuum to the EGR valve. This test result tells you the EGR valve is bad and indicates one of two issues (with the EGR valve):

• The EGR valve's rubber diaphragm is bad.
• The EGR valve's pintle is stuck due to carbon buildup.

Remove and replace the EGR valve. Since you're removing the EGR valve, you can bench-test it: TEST 3: Bench Testing The EGR Valve.

CASE 4: The engine's smooth idle DID NOT become rough, but the pintle rose when you applied vacuum to the EGR valve. This test result generally tells you the EGR valve is OK but that the EGR passages are blocked somewhere between the EGR valve and the intake manifold.

To be more specific, this test result usually indicates one of two things:

• The EGR passages in the valve's adapter are blocked.
• The EGR passages in the intake manifold are blocked.

To further investigate this, go to: TEST 5: Checking For Blocked EGR Passages.

TEST 3: Bench Testing The EGR Valve

The EGR valve used in your 2.2L Chevy S10 (GMC Sonoma) is a negative back pressure EGR valve.

In plain English, this means we can easily bench test it off of the engine with a vacuum pump to check the movement of its rubber diaphragm and pintle.

If the EGR valve is bad, you'll see one or both of the following:

• The valve's rubber diaphragm will not move up/down as you apply/release vacuum to it.
• The valve's pintle will not move up/down as you apply/release vacuum to it.

NOTE: To find out more about negative and positive back pressure EGR valves, see: How Can I Tell If I Have A Negative Or Positive Back Pressure EGR Valve?

Let's get started:

1. 1

   Remove the EGR valve from its location.
   
   CAUTION: The EGR valve can get hot. You many need to let the engine cool down before removing it.

2. 2

   Connect your vacuum pump to the EGR valve.

3. 3

   Apply vacuum to the EGR valve.

4. 4

   You should see the EGR valve's diaphragm and pintle move up as you apply vacuum.

5. 5

   Hold (maintain) the vacuum applied to the valve for a few seconds.

6. 6

   The diaphragm and pintle should not move (return to their closed position) while you're maintaining vacuum to the EGR valve.

7. 7

   Release the vacuum you applied to the EGR valve.

8. 8

   You should see the EGR valve's diaphragm and pintle move back to their original positions.

9. 9

   Repeat steps 3 thru 8 several times to make sure of your test results.

Let's interpret your test result:

CASE 1: The diaphragm/pintle moved up/down as you applied/released vacuum AND the diaphragm/pintle did not return to their closed position when you held the vacuum. This test result confirms the EGR valve is functioning correctly.

If, in TEST 2, the engine's idle did not worsen when you applied vacuum to the EGR valve (with the engine running), you can conclude that either:

• The EGR valve adapter has its passages block with carbon.
• The intake manifold's EGR port is blocked with carbon.

If you suspect the EGR passages are blocked with carbon, go to: TEST 5: Checking For Blocked EGR Passages.

CASE 2: The EGR valve's diaphragm DID NOT move up/down as you applied/released vacuum to the valve. This test result confirms that the EGR valve is bad. Replace the EGR valve.

IMPORTANT: This test interpretation only applies if the EGR valve is a negative back pressure EGR valve type.