How To Test The EGR Valve (1988-1995 4.3L TBI Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

TEST 4: Checking For Blocked EGR Passages

Your previous tests have confirmed:

• The EGR valve IS NOT receiving vacuum when the engine is idling (TEST 1).
• Applying vacuum to the EGR valve (with the engine at 2000 RPM) does not affect engine RPM (TEST 2).
• Manually pushing the EGR valve's diaphragm open (with the engine at idle RPM) does not affect engine RPM (TEST 3).

There's a good possibility that carbon buildup on the EGR valve or on the intake manifold are blocking the exhaust gas flow.

In this test section, we'll remove the EGR valve and inspect the exhaust gas passages in the intake manifold and EGR valve.

IMPORTANT: If the engine has been running for any length of time and the EGR valve is hot, wait till the engine cools down completely before removing the EGR valve.

Let's get started:

1. 1

   Remove the EGR valve from its place on the engine.
   
   NOTE: Place all the nuts and bolts (you remove) away from the engine compartment to prevent any of them from falling into open intake manifold EGR ports.

2. 2

   Visually inspect the orifices on the EGR valve itself for carbon accumulation and blockage.

3. 3

   Visually inspect the the intake manifold EGR ports for carbon accumulation and blockage.

Let's interpret your test result:

CASE 1: Carbon is not blocking any of the EGR orifices or ports. This is the correct and expected test result.

You can conclude the EGR valve is bad and needs replacement if you have confirmed:

• The EGR valve IS NOT receiving vacuum when the engine is idling (TEST 1).
• Applying vacuum to the EGR valve (with the engine at 2000 RPM) has no effect on engine RPM (TEST 2).
• Manually pushing the EGR valve's diaphragm open (with the engine at idle RPM) has no effect on engine RPM (TEST 3).
• The EGR valve and the intake manifold ports (facing the EGR valve) are not blocked with carbon buildup (this test section).

CASE 2: Carbon buildup blockage is present. Clean/remove the carbon.

Use caution to keep the carbon from falling into the intake manifold and be careful not to damage gasket surfaces.

Once you've cleaned/removed the carbon buildup blockage, reinstall the EGR valve and road test the vehicle to see if the EGR valve code or EGR system issue has been resolved.

EGR Valve Code Keeps Coming Back

In some cases, the EGR valve diagnostic trouble code 32 keeps coming back even after the EGR valve is replaced.

If this is what's happening in your case, there's a good chance the intake manifold's internal EGR gas passage is blocked by carbon buildup. Specifically:

• The EGR gas channel inside the intake manifold is blocked with carbon buildup.
• The intake manifold EGR port (the one that faces the cylinder head) is blocked with carbon buildup.
• The cylinder head EGR port (the one that faces the intake manifold) is blocked with carbon buildup.

Generally, this condition can only be determined by removing the intake manifold and doing a visual inspection of:

• The EGR port on the intake manifold facing the cylinder head.
• The EGR port on the cylinder head facing the intake manifold.

If the ports are blocked with carbon buildup, scrape it off being careful not to damage the gasket surfaces.

Once the carbon buildup blockage has been removed, reinstall everything and road test the vehicle.