How To Test The EGR Valve (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

TEST 4: Checking For Blocked EGR Passages

If you've reached this point, you have confirmed the following:

• The EGR valve is NOT receiving vacuum when the engine is idling (TEST 1).
• Engine speed is not affected when vacuum is applied to the EGR valve with a vacuum pump (TEST 2).
• Engine speed is not affected when the EGR valve diaphragm is opened manually (TEST 3).

It's not uncommon for carbon buildup on the EGR valve or intake manifold to block 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 to see if there's carbon deposit blockage.

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

If replacing the EGR valve does not prevent code 32 from coming back and illuminating the check engine light, there's a good chance that the intake manifold's internal EGR gas passage is blocked by carbon deposits.

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.

More 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup Tutorials

You can find a complete list of 2.8L V6 Chevrolet S10 pickup, GMC S15 pickup, and GMC Sonoma diagnostic tutorials in this index:

• GM 2.8L Index Of Articles.

Here's a sample of the articles, you'll find in the Index of Articles:

• How To Test The MAP Sensor With A Multimeter (2.8L Chevy S10, GMC S15).
• Vacuum Hose Routing Diagram 1988 GM 2.8L S10/S15.
• How To Test For A Bad Alternator (2.8L V6 S10/S15).
• How To Test Engine Compression (2.8L S10 Pickup/Blazer).