yo j,
Is trans fluid level ok and color ok? No aroma of burnt toast?
Has engine overheated recently?
Some ideas;
VACUUM:
Ensure all vacuum hoses are connected and not leaking (sounds like a Hiss when using a short section of garden hose or a mechanic's stethoscope for under $5.00 @ parts store or Harbor Freight)..check;
vacuum diaphragm on transmission
a4ld vacuum diaphragm.pdf ensure hose is not damaged or leaking back to its source; I don't have info on how to test that A4LD vacuum diaphragm but usual Ford tests is checking for trans fluid in that hose .. if fluid id in hose, could be a ruptured diaphragm.
Removal
1.Disconnect the negative battery cable.
2.Raise and support the vehicle safely. CHOCK WHEELS; DO NOT USE BUMPER JACK; Support WITH Jack Stands of suitable rating.
3.Disconnect the hose from the vacuum diaphragm.
4.Remove the vacuum diaphragm retaining clamp bolt and clamp. Do not pry on the clamp.
5.Pull the vacuum diaphragm from the transmission case and remove the vacuum diaphragm control rod from the transmission case.
To install:
6.Install the vacuum diaphragm control rod from the transmission case.
7.Push the vacuum diaphragm into the case and secure it with the clamp and bolt. Tighten to 80-106 inch lbs. (9-12Nm).
8.Fit the vacuum hose to the diaphragm.
9.Lower the vehicle.
10.Reconnect the negative battery cable.
Also check MAP sensor & brake booster hoses and the units themselves for Vac leaks , Emission system as well as HVAC system (in engine bay and under dash) hoses & components can be vac leak sources.
When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. ALWAYS SERVICE VACUUM LEAKS.
87 BII 2.9 Vacuum Diagram
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Ford TSB 97-22-4 Date: 10/27/97
Transmission - A4LD, 4R44E/4R55E, 5R55E - Torque Converter Slip - Diagnostic Trouble Code (Dtc) 628 Or P0741 Stored In Memory
Ford:
1985 to 1993 Mustang
1987 to 1988 Thunderbird
Lincoln-Mercury:
1988 Cougar
Light Truck:
1985 to 1990 Bronco II
1985 to 1997 Ranger
1987 to 1997 Aerostar
1991 to 1997 Explorer
ISSUE:
Some vehicles may experience excessive torque converter slippage, torque converter not engaging, or Diagnostic Trouble Code (DTC) 628 stored in memory. This may be caused by damage to the fluid pump support seal and/or to the groove on the pump where the seal is located.
ACTION:
Inspect the fluid pump seal for damage. Refer to the following Service Procedure for details.
SERVICE PROCEDURE:
Follow normal diagnostic procedures as listed in the appropriate Service Manual.
Inspect the fluid pump support for damage. If damaged, also inspect the fluid pump support seal groove on the pump.
If the groove is damaged, replace the pump.
If the groove is not damaged, replace the fluid pump support seal with a redesigned Seal (F77Z-7L323-AA). Refer to Figure 1.
Do not replace the torque converter unless it is damaged or fails the criteria listed in the appropriate Service Manual and/or refer to TSB 96-26-12.
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