Rough Idle and Dinging noises when in Gear.

[Dads93Mark3]

1993 OBS 350 TBI. When I’m in park the engine revs and idles great. When I put it in gear it starts a rough idle and feels like it’s skipping. Once I’m up into the gears (4L80E) and I try to accelerate, I hear a dinging or clanging noise almost like valve train noises. Garage guy said it was a vacuum line. He replaced one and it’s still bad. Thoughts?

 

[scott2093]

Have you looked at the timing?

 

[Dads93Mark3]

Have you looked at the timing?

No but I will.

 

[Schurkey]

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)
2. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Make sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing (TBI) and electronic spark advance (TBI and Vortec). Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.
3. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. Look for misfire counts for each cylinder (OBD2 only.) “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle. The service manual set can be downloaded from the links in the Sticky thread section of the Engine forum on this web site.

 

[Dads93Mark3]

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)
2. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Make sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing (TBI) and electronic spark advance (TBI and Vortec). Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.
3. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. Look for misfire counts for each cylinder (OBD2 only.) “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle. The service manual set can be downloaded from the links in the Sticky thread section of the Engine forum on this web site.

Thanks for the information. I’ll start checking them all off. Plugs are new, but a can’t remember about the cap. I’ll check it all out. Thanks again.

 

[Dads93Mark3]

Have you looked at the timing?

The timing is set dead on 0

 

[scott2093]

When I put it in gear it starts a rough idle and feels like it’s skipping. Once I’m up into the gears (4L80E) and I try to accelerate, I hear a dinging or clanging noise almost like valve train noises.

Drivetrain noise you mentioned....?

Wonder if flexplate>torque converter>transmission...etc comes into play for any of this

 

[Dads93Mark3]

Drivetrain noise you mentioned....?

Wonder if flexplate>torque converter>transmission...etc comes into play for any of this

The flex plate was the first thought too. I’m taking it to a guy today. So I’ll update later

 

[GoToGuy]

Not obs. Model, C1500, K2500, Tahoe. etc.

 

[Dads93Mark3]

Not obs. Model, C1500, K2500, Tahoe. etc.

C1500