I just sent this to the site owner. He feels it could be a broken valve spring or even a flat spot on the cam. Let's do this. Let's remove the valve covers and check for a broken spring.
Here are the directions for both sides. Remove them and see if there are any broken springs. The attached pics correlate with the directions.
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1999 Chevy Truck S10/T10 P/U 2WD V6-4.3L VIN W
Valve Rocker Arm Cover Replacement (Right)
Vehicle Engine, Cooling and Exhaust Engine Cylinder Head Assembly Valve Cover Service and Repair Procedures Valve Rocker Arm Cover Replacement (Right)
VALVE ROCKER ARM COVER REPLACEMENT (RIGHT)
Removal Procedure
pic 1
1. Remove the PCV tube from the air cleaner outlet duct and the valve rocker arm cover.
2. Disconnect the spark plug wires from the spark plugs for the right side of the engine. Refer to Spark Plug Wire Harness Replacement in Powertrain Management.
3. Remove the EVAP canister purge solenoid valve. Refer to EVAP Canister Purge Solenoid Valve Replacement in Powertrain Management.
4. Unfasten the heater hose retainer above the valve rocker arm cover.
5. Move and secure the heater hoses aside.
pic 2
6. Remove the bolt holding the engine wiring harness bracket to the generator.
7. Disconnect the Crankcase Position (CKP) sensor electrical connector.
8. Move and secure the engine wiring harness aside.
pic 3
9. Remove the bolts and the right valve rocker arm cover.
10. Clean all sealing surfaces. Refer to Valve Rocker Arm Cover Clean and Inspect
Installation Procedure
pic 4
1. Install the right valve rocker arm cover and bolts. Refer to Valve Rocker Arm Cover Installation (Right).
pic 5
2. Position the engine wiring harness.
3. Connect the CKP sensor electrical connector.
Notice: Refer to Fastener Notice in Service Precautions.
4. Install the engine wiring harness and bolt to the generator mounting bracket.
Tighten the engine wiring harness bolt to 25 Nm (18 ft. lbs.).
5. Position the heater hoses.
6. Install the heater hoses in the retainer above the valve rocker arm cover.
7. Install the EVAP canister purge solenoid valve. Refer to EVAP Canister Purge Solenoid Valve Replacement in Powertrain Management.
pic 6
8. Connect the spark plug wires to the spark plugs for the right side of the engine. Refer to Spark Plug Wire Harness Replacement in Powertrain Management.
9. Install the PCV tube to the air cleaner outlet duct and the valve rocker arm cover.
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Left Side
1999 Chevy Truck S10/T10 P/U 2WD V6-4.3L VIN W
Valve Rocker Arm Cover Replacement (Left)
Vehicle Engine, Cooling and Exhaust Engine Cylinder Head Assembly Valve Cover Service and Repair Procedures Valve Rocker Arm Cover Replacement (Left)
VALVE ROCKER ARM COVER REPLACEMENT (LEFT)
Removal Procedure
pic 7
1. Remove the air cleaner outlet duct from the throttle body. Refer to Air Cleaner Outlet Duct Replacement in Powertrain Management.
2. Remove the air cleaner assembly. Refer to Air Cleaner Assembly Replacement in Powertrain Management.
3. Remove the PCV valve hose assembly from the valve rocker arm cover.
4. Disconnect the Engine Coolant Temperature (ECT) gauge sensor.
5. Partially drain the engine coolant. Refer to Draining and Filling Cooling System in Cooling System.
6. Remove the radiator inlet hose from the water outlet. Refer to Radiator Hose Replacement in Cooling System.
pic 8
7. Remove the Exhaust Gas Recirculation (EGR) valve inlet pipe from the intake manifold and the exhaust manifold.
pic 9
Important: A/C compressor and bracket removal is not necessary.
8. Remove the bolts and the valve rocker arm cover.
9. Clean all sealing surfaces. Refer to Valve Rocker Arm Cover Clean and Inspect.
Installation Procedure
pic 10
1. Install the valve rocker arm cover and bolts.
pic 11
Notice: Refer to Fastener Notice in Service Precautions.
2. Install the exhaust gas recirculation (EGR) valve inlet pipe into the intake and exhaust manifolds.
2.1. Tighten the EGR valve inlet pipe intake manifold nut to 25 Nm (18 ft. lbs.).
2.2. Tighten the EGR valve inlet pipe exhaust manifold nut to 30 Nm (22 ft. lbs.).
2.3. Tighten the EGR valve inlet pipe clamp bolt to 25 Nm (18 ft. lbs.).
pic 12
3. Install the radiator inlet hose to the water outlet. Refer to Radiator Hose Replacement in Cooling System.
4. Fill the cooling system. Refer to Draining and Filling Cooling System in Cooling System.
5. Install the PCV valve hose assembly to the valve rocker arm cover.
6. Connect the ECT gauge sensor.
7. Install the air cleaner assembly. Refer to Air Cleaner Assembly Replacement in Powertrain Management.
8. Install the air cleaner outlet duct to the throttle body. Refer to Air Cleaner Outlet Duct Replacement in Powertrain Management.
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If you look at the last pic, I highlighted the valve springs.
Also, I would suggest checking engine compression. That can tell us a lot as well. Here is a link showing how that is done.
https://www.2carpros.com/articles/how-to-test-engine-compression
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One last check. Once the valve covers are off, have a helper crank the engine while you make sure all of the valves are moving up and down. If they are, great. If you find one that isn't, that would likely mean one of the lobes is worn on the camshaft.
Let me know what you find or if you have other questions.
Take care,
Joe
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Thursday, February 4th, 2021 AT 6:15 PM