Engine - Piston Knock at Idle
NO: 09-03-94GROUP: Engine
DATE: Apr. 1, 1994
SUBJECT:
Engine Idle Piston Noise
MODELS:
1990 - 1993 (AC) Dynasty/New Yorker/New Yorker Salon
1990 - 1994 (AS) Caravan/Voyager/Town & Country
1990 - 1993 (AY) Imperial/New Yorker Fifth Avenue
1993 - 1994 (LH) Concorde/intrepid/Vision
NOTE:
THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH THE 3.3L AND 3.8L ENGINE
SYMPTOM/CONDITION:
Cold start up piston knocking noise at idle that diminishes 3 to 5 minutes after start up. The condition is more prominent in low ambient temperatures and after the vehicle has set overnight.
Similar symptoms are described in Technical Service Bulletin 09-21-93 dated Dec. 31, 1993, "Carbon Buildup on Top of Piston". Refer to this Bulletin for additional details.
DIAGNOSIS:
Using the Mopar Diagnostic System or the Scan Tool (DRB II) with appropriate diagnostic procedure manual, verify that all engine systems are functioning as designed. If Diagnostic Trouble Codes (DTC's) are present, record them on the repair order for future reference, and repair as necessary. If no codes are present and all systems are functioning correctly, and carbon buildup on the top of the piston is not evident, proceed with the following repair.
PARTS REQUIRED:
AR 4621978 Piston & Connecting Rod Assy. (use w/3.3L engine)
AR 4621981 Piston & Connecting Rod Assy. (use w/3.8L engine)
REPAIR PROCEDURE:
This repair involves installing a new coated piston and connecting rod assembly.
1. Following the procedure outlined in the appropriate Service Manual, remove the engine piston and connecting rods.
2. Install the new coated piston and connecting rod assembly as outlined in the Service Manual.
NOTE:
HONING OF THE CYLINDER BORES IS NOT RECOMMENDED.
DISCUSSION:
The new pistons have a coating bonded only to the piston skirt that is black in appearance. This new coating replaces the previously used tin coating.
Items of special interest include:
1. The new coated pistons are available in one size only and are serviced with the piston pin and connecting rod as an assembly.
2. The new coated piston connecting rod assembly can be used to service all models listed and can be replaced one at a time (complete engine sets are not required).
3. Tin coated pistons should not be used as replacements for the coated pistons.
4. The coating material is applied after the final piston machining process. Therefore, the step for measuring the outside diameter of the piston to determine size or piston to bore clearance is not required.
5. Measuring the inside diameter of the cylinder bore with a Bore Gauge is still required. Dial Cylinder Bore Indicator, Tool C-119 available from Miller Special Tools, is recommended. Follow the procedure outlined in the Service Manual.
If the cylinder bore measures larger than 3.664 inches (93.059 mm) for the 3.3L Engine, or 3.782 inches (96.059 mm) for the 3.8L Engine, the cylinder block will require replacement.
6. Piston installation into the cylinder bore may require slightly more pressure than that required for non-coated pistons. The bonded coating on the piston will give the appearance of a line-to-line fit with the cylinder bore.
POLICY: Reimbursable within the provisions of the warranty.
TIME ALLOWANCE:
1990 - 1994 AC, AS, AY (W/3.3L or 3.8L Engine)
Piston and Connecting Rod Replace
Labor Operation No.
09-70-01-91 One - Front Bank 4.2 Hrs.
09-70-01-92 One - Rear Bank 4.5 Hrs.
09-70-01-93 One - Each Bank 6.0 Hrs.
09-70-01-94 Each Additional 0.5 Hrs.
09-70-01-63 A/C Equipped 0.2 Hrs.
09-70-01-64 Power Steering Equipped (AS Only) 0.2 Hrs.
1993 - 1994 LH (w/3.3L or 3.8L Engine)
Piston and Connecting Rod Replace
Labor Operation No.
09-70-01-95 One - Left Bank 4.1 Hrs.
09-70-01-96 One - Right Bank 3.7 Hrs.
09-70-01-97 One - Each Bank 5.2 Hrs.
09-70-01-98 Each Additional 0.5 Hrs.
09-70-01-63 A/C Equipped 0.3 Hrs.
FAILURE CODE: 58 - Noisy Cold Only