Torque Converter Stall Test
Torque Converter Stall Testing:
The torque converter stall test is used primarily to determine stator overrunning clutch operation and any clutch for holding power chosen by the DRB scan tool.
Use the DRB or equivalent scan tool and a tachometer to do the stall test.
Determine engine rpm with the transaxle in drive, engine at wide open throttle, and vehicle stationary.
To keep the vehicle stationary, and to avoid creeping or lurching forward, apply both the service brakes and the parking brake.
WARNING: When performing a stall test, always apply both the service brakes and parking brake. Also, do not let anyone stand in front of the vehicle during testing.
CAUTION: Avoid keeping the throttle open for more than 5 seconds at a time. Allow the transmission fluid to cool between stall tests by placing the transaxle in neutral, raising the engine rpm slightly for approximately 20 seconds.
TORQUE CONVERTER STATOR CLUTCH FAILURE
One type of stator over-running clutch failure is a slipping clutch. With this type of failure, the vehicle will exhibit normal transaxle operation at highway speeds but will have poor acceleration.
Another type of stator over-running clutch failure is a seized clutch.
With this type of failure, the vehicle acceleration may be acceptable but a high throttle is required to maintain vehicle speed.
The vehicle may seem like it has a loss of power.
With either type of failure, poor fuel economy and transaxle fluid over-hearting may be the result.
STALL SPEED ABOVE SPECIFICATION
If the stall speed exceeds 2,440 r/min by more than 200 r/min, a clutch is slipping.
Diagnose the clutch circuits by performing hydraulic and air pressure tests.
The clutches of the F4AC1 transaxles may also be checked using information given through the input and output speed sensors to the EATX-ECM. By using the DRB or equivalent scan tool, the technician can cause the EATX-ECM to apply a particular clutch (clutches the EATX-ECM has control over).
STALL SPEED BELOW SPECIFICATION
If stall speed is 250-350 r/min below specification, the stator over-running clutch is slipping. During the road test, if poor acceleration occurs through the gears with normal transaxle operation at highway speeds, the vehicle has a slipping stator clutch.
NORMAL STALL SPEED AND ACCELERATION
If stall speed and acceleration appear normal, but it takes excessively high throttle opening to maintain vehicle speed, the starter's over-running clutch is seized.
This will impede the flow of fluid within the torque converter causing excessive use of power from the engine for cruising.
CONVERTER NOISE
While performing the stall test, listen for abnormal noise coming from the converter area.
A whining noise due to fluid flow within the converter is considered normal.
Loud metallic noises coming from the converter indicate loose parts or internal damage. Remove the inspection cover from the bellhousing area and check for a cracked torque converter flex plate or its bolts.
If the flex plate and bolts are ok, and there is still noise coming from the torque converter, the torque converter may be defective and must be replaced.
Be sure to check a sample of the fluid for contamination.
CAUTION: TRANSAXLE COOLER AND LINE FLUSHING
- If there has been a mechanical failure within the torque converter or in the transaxle itself, the fluid becomes contaminated and circulates throughout the hydraulic system. This includes the cooler for the transaxle inside the radiator. The cooler and the lines connecting the cooler to the transaxle, must be flushed before being connected to the newly repaired or replaced torque converter or transaxle.
- If the system is not flushed, the new components will become contaminated with the old fluid. The proper method for flushing is reverse flushing the system.