MX-5 Miata L4-1597cc 1.6L DOHC (1992)
Oil Pump: All Technical Service Bulletins
Oil Pump - Engine Stall/Rough Idle on Cold Start
Bulletin No.: 002/96
Issued: 09/09/96
Revised:
Category
D
Applicable Model/s
See Below
Subject:
ROUGH IDLE AND/OR ENGINE STALL AFTER COLD START
AFFECTED MODELS
1994 - 96 323/Protege with the following engines: B6 and BP
1994 - 96 MX-3 with B6 engine.
1990 - 96 MX-5 with B6 and BP engines.
1994 - 96 626/MX-6 with a 4 cyl. engine and a VIN 1YVGE**C*T5580486 and lower.
DESCRIPTION
Rough idle and/or engine stall may occur after cold start and continue until the engine reaches normal operating temperature. This condition may occur
in cold ambient temperatures 14 degrees to 50 degrees (F) (-10 degrees to 10 degrees C).
The following causes may result in poor driveability in cold ambient temperatures:
1.
Vehicles with long oil pump control plungers as a countermeasure for HLA noise.The concern may be caused when the oil pump control plunger
becomes struck When this occurs, the oil pressure becomes excessive. The high pressure is applied directly to the HLA, which pushes the valve
down and prevents complete dosing.
^
To prevent this concern, the plunger has been modified.
2.
B6 DOHC Engines Only Compression loss due to poor seating of the exhaust valve caused by thermal expansion.
^
To prevent this occurrence, an exhaust valve stem with low thermal expansion coefficient is used.
^
A stronger valve spring is used so that the HLA will absorb the valve's expansion during cold ambient temperatures.
DIAGNOSTIC PROCEDURE
Follow this procedure if the vehicle has a B6 DOHC engine. If the vehicle is not equipped with a B6 DOHC engine, perform REPAIR 1.
^
Allow the vehicle to sit for at least eight hours (overnight) in cold ambient temperatures [50 degrees F (10 degrees C)].
1.
Prepare to measure the engine oil pressure.
2.
Start the engine.
3.
Measure the oil pressure immediately after starting (during fast idle).
^
If the pressure is approximately 784 kPa (8.0 kgf/cm, 112 psi) or more, the cause may be a stuck oil plunger. Proceed to REPAIR 1.
^
If the pressure is approximately 490 kPa (5.0 kgf/cm, 70 psi) the concern may be caused by exhaust valve expansion. Proceed to REPAIR 2.
NOTE:
If the diagnostic inspection is inconclusive, proceed to step 4.
4.
Allow the engine to run for 2 or 3 minutes.
5.
Raise engine RPM to 3,000.
6.
Measure the oil pressure.
^
If the oil pressure is not significantly different from the first measurement the problem may be caused by exhaust valve expansion.
^
If the pressure is over 980 kPa (10 kgf/cm, 140 psi) the cause may be a stuck oil plunger.
REPAIR 1
