Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1990R 20 P/U 2WD V8-454 7.4LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTTRANSMISSION CONTROL SYSTEMSTECHNICAL SERVICE BULLETINSCUSTOMER INTERESTA/T - BUZZING NOISE AT IDLE
1990 Chevrolet R 20 P/U 2WD V8-454 7.4L
A/T - Buzzing Noise at Idle
1990 Chevrolet R 20 P/U 2WD V8-454 7.4LSECTION A/T - Buzzing Noise at Idle
Number: 93-29-7A
Section: 7A
Date: OCT. 1992
Corporate Bulletin No.: 277142
ASE No.: A2
Subject:
BUZZING NOISE AT IDLE
Model and Year:
1982-93 CAPRICE, CAMARO AND CORVETTE
1982-93 C/K, R/V, S/T, M/L AND G TRUCKS WTIH 4L60 AUTOMATIC TRANSMISSION
TRANSMISSION APPLICATIONS:
1982-1993 HYDRA-MATIC 4L60 (MD8)
TRANSMISSION MODELS:
All
SUBJECT:
Pressure Regulator Valve Buzz
VEHICLE APPLICATIONS:
B, D, F, Y - Cars C/K, R/V, S/T Trucks G, M, L - Vans
CONDITION:
Some 1982-1993 vehicles equipped with a HYDRA-MATIC 4L60 transmission may have a buzzing noise coming from the transmission when the vehicle is at idle. The buzzing noise may be noticed more when the vehicle is in reverse at idle.
CAUSE:
The buzzing noise may be a result of pressure regulator valve oscillating due to oil pressure instability at lower idle RPM.
CORRECTION:
A new pressure regulator valve (III. 218) has been made which will improve the oil pressure stability at lower RPM.
SERVICE PARTS INFORMATION:
Description Part Number
Valve, Pressure Regulator (III. 218) 8684048
Part numbers are for Reference Only.
Check with your Parts Department for latest information.
Labor Operation No.: K6550 Valve, Pressure Regulator-R&R or Replace
Use the appropriate labor time in the labor time guide.
Parts are currently available from GMSPO.
Section: 7A
Date: OCT. 1992
Corporate Bulletin No.: 277142
ASE No.: A2
Subject:
BUZZING NOISE AT IDLE
Model and Year:
1982-93 CAPRICE, CAMARO AND CORVETTE
1982-93 C/K, R/V, S/T, M/L AND G TRUCKS WTIH 4L60 AUTOMATIC TRANSMISSION
TRANSMISSION APPLICATIONS:
1982-1993 HYDRA-MATIC 4L60 (MD8)
TRANSMISSION MODELS:
All
SUBJECT:
Pressure Regulator Valve Buzz
VEHICLE APPLICATIONS:
B, D, F, Y - Cars C/K, R/V, S/T Trucks G, M, L - Vans
CONDITION:
Some 1982-1993 vehicles equipped with a HYDRA-MATIC 4L60 transmission may have a buzzing noise coming from the transmission when the vehicle is at idle. The buzzing noise may be noticed more when the vehicle is in reverse at idle.
CAUSE:
The buzzing noise may be a result of pressure regulator valve oscillating due to oil pressure instability at lower idle RPM.
CORRECTION:
A new pressure regulator valve (III. 218) has been made which will improve the oil pressure stability at lower RPM.
SERVICE PARTS INFORMATION:
Description Part Number
Valve, Pressure Regulator (III. 218) 8684048
Part numbers are for Reference Only.
Check with your Parts Department for latest information.
Labor Operation No.: K6550 Valve, Pressure Regulator-R&R or Replace
Use the appropriate labor time in the labor time guide.
Parts are currently available from GMSPO.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.