Control or Line Pressure Test
CONTROL PRESSURE TESTNOTE: There are two methods performing the control pressure test. One is to perform the test using engine vacuum. The second is to use a remote vacuum source such as the one provided by a distributor tester or a hand operated vacuum pump.
Engine Vacuum Pressure
Shift Speed Chart, (1988 Mustang W/2.3L Engine):
Shift Speed Chart, (1988 Thunderbird Turbo Coupe W/2.3L Engine):
Shift Speed Chart, (1988 Ranger W/2.3L Engine):
Shift Speed Chart, (1988 Bronco II And Ranger W/2.9L Engine):
Shift Speed Chart, (1988 Aerostar W/3.0L Engine, Except Nos. 88GT-LAB And 88GT-MAB):
Shift Speed Chart, (1989-1991 Mustang W/2.3L Engine, Except 1990 California Models):
Shift Speed Chart, (1989-1991 Ranger W/2.3L Engine, Except 1990 California Models):
Shift Speed Chart, (1989-1990 Bronco II And 1989-1991 Ranger W/2.9L Engine):
Shift Speed Chart, (1989-1991 Aerostar And 1991 Ranger W/3.0L Engine, Except 1989 Aerostar Model Nos. 89GT-EAA And 89GT-EAB):
Shift Speed Chart, (1990 Mustang W/2.3L Engine, California):
Shift Speed Chart, (1990 Ranger W/2.3L Engine, California):
Shift Speed Chart, (1990-1991 Ranger W/4.0L Engine):
Shift Speed Chart, (1990-1991 Aerostar W/4.0L Engine, Model Nos. 90GT-ADA, 90GT-ADD, 90GT-AEA, 90GT-AEE, 91GT-SCA, 91GT-SDA, 91GT-SEA, And 91GT-SFA):
Shift Speed Chart, (1990-1991 Aerostar W/4.0L Engine, Model Nos. 90GT-EAA, 90GT-EBA, 90GT-FAA, 90GT-FBA, 91GT-GAA, 91GT-HAA, 91GT-SAA, And 91GT-SBA):
Shift Speed Chart, (1991 Explorer W/4.0L Engine, Model Nos. 91GT-AAA, 91GT-BAA, 91GT-DAA, And 91GT-EAA):
1. When the vacuum diaphragm unit is operating properly and the manual and downshift linkage is adjusted properly, all transmission shifts (automatic and kickdown) should occur within the specified road speed limits, as shown in the Shift Speed Charts.
2. If shifts do not occur within limits, or the transmission slips during the shift point test, use one of the following procedures to determine whether the engine, transmission, linkage, vacuum diaphragm unit, or valve body is causing the condition.
Engine Vacuum Method
Vacuum Line Test Connections:
1. Attach a tachometer to engine and a vacuum gauge to transmission vacuum line at the manifold vacuum port, as shown in the Vacuum Line Test Connections image.
Control Pressure Connecting Point:
2. Attach a pressure gauge to the control pressure outlet at the transmission, as shown in the Control Pressure Connecting Point image.
CAUTION: Pressure gauges affect transmission shift quality. Rapid acceleration or deceleration may cause transmission failure.
3. Firmly apply parking brake and start engine.
4. Adjust engine idle speed to specifications. If idle speed cannot be adjusted to specifications, check throttle and downshift linkages for a binding condition. If linkage is satisfactory, check for vacuum leaks in transmission diaphragm unit and its connecting tubes and hoses. Check all other vacuum operated units for leaks.
Control Pressure Test Charts:
Control Pressure Specifications, (Part 1 Of 2):
Control Pressure Specifications, (Part 2 Of 2):
5. Refer to control pressure diagnostic guides, Control Pressure Test Charts, to determine which components are inoperative when the control pressure test is not within specifications, as shown in the Control Pressure Specifications Charts.
Vacuum Pump Method
1. Install automatic transmission tester or equivalent and temporarily plug vacuum line at vacuum diaphragm unit.
2. Apply both parking and service brakes, start engine and vacuum pump, set vacuum at 15 inches and read and record control pressure in all selector positions.
3. Run the engine up to 1,000 RPM, reduce vacuum to 10 inches and read and record control pressure in OD, D, 2, and 1.
4. keep the engine at 1,000 RPM, reduce vacuum to 1 inch and read and record control pressure in OD, D, 2, 1. and R.
5. Refer to control pressure diagnostic guides, Control Pressure Test Charts image, to determine which components are inoperative when the control pressure is not within specifications, as shown in the Control Pressure Specifications charts.