Engine - Rough Idle, Compression Specifications

Classification:
EM93-001

Section:
Engine Mechanical

Reference:
TECHNICAL BULLETIN NTB93-105

Models:
1990-91 300ZX

Date:
July 8, 1993

1990-91 300ZX ROUGH IDLE

APPLIED MODEL
1990-91 300ZX
1990-91 300ZX Turbo

APPLIED ENGINE #
Non-Turbo VG30-777599
Turbo VG30-619550

APPLIED DATE
Non-Turbo June 22, 1990
Turbo December 11, 1989

SERVICE INFORMATION





On some 1990-91 300ZX vehicles, customers may complain of a rough idle which may be caused by wear of the engine intake valves. (Figure 1)

If this incident has occurred, a countermeasure intake valve is available to resolve the incident. The treatment process applied to the intake valve seat face has been changed.

SERVICE PROCEDURE

1. Perform a compression test on the engine.

Compression Test Specifications:
Non-Turbo Turbo
Standard 1,285 (13.1, 186) 1,177 (12.0, 171)
Minimum 981 (10.0, 142) 883 (9.0, 128)
Differential limit between cylinders 98 (1.0, 14) 98 (1.0, 14)

Units: kPa (kg/sq.mm, psi)/300 rpm

2. If the compression pressure test was lower than specification, then perform a cylinder leakdown test to determine the exact source of leakage. If leakage is found past the valves, remove cylinder heads.

3. Remove all of the valves, inspect valves and valve seat mating area.

4. If there is wear on the valve seat inserts, reform the valve seat with a valve seat cutter.
(Refer to Service Manual for Seat Specifications)

5. Apply abrasive compound to the valve seat inserts and lap valve seats with new intake valves. Clean valves and valve seats thoroughly to remove all traces of abrasive compound.

6. Clean and re-assemble cylinder heads and install onto cylinder block.

7. Check that compression pressure is now to specification.

PARTS INFORMATION:

DESCRIPTION NEW P/N Former P/N

Valve-Intake 13201-F6511 13201-30P00





WARRANTY INFORMATION: