Converter Stall Test

CONVERTER STALL TEST
Stall testing involves determining maximum engine speed obtainable at full throttle with the rear wheels locked and the transmission in D range. This test checks the holding ability of the converter overrunning and transmission clutches.

WARNING: Never allow anyone to stand directly in line with the vehicle front or rear during a stall test. Always block the wheels and fully apply the service and parking brakes during the test.

STALL TEST PROCEDURE
1. Connect tachometer to engine. Position tachometer so it can be viewed from driver's seat.
2. Drive vehicle to bring transmission fluid up to normal operating temperature. Vehicle can be driven on road or on chassis dynamometer, if available.
3. Check transmission fluid level. Add fluid if necessary.
4. Block front wheels.
5. Fully apply service and parking brakes.
6. Open throttle completely and record maximum engine speed registered on tachometer. It takes 4-10 seconds to reach max rpm. Once max rpm has been achieved, do not hold wide open throttle for more than 4-5 seconds.

CAUTION: Stalling the converter causes a rapid increase in fluid temperature. To avoid fluid overheating, hold the engine at maximum rpm for no more than 5 seconds. If engine exceeds 2500 rpm during the test, release the accelerator pedal immediately; transmission clutch slippage is occurring.

7. If a second stall test is required, cool down fluid before proceeding. Shift into NEUTRAL and run engine at 1000 rpm for 20-30 seconds to cool fluid.

STALL TEST ANALYSIS
Stall Speed Too High
If the stall speed exceeds 2500 rpm, transmission clutch slippage is indicated.

Stall Speed Low
Low stall speed with a properly tuned engine indicate a torque converter overrunning clutch problem. The condition should be confirmed by road testing. A stall speed 250-350 rpm below normal indicates the converter overrunning clutch is slipping. The vehicle also exhibits poor acceleration but operates normally once highway cruise speeds are reached. Torque converter replacement will be necessary.

Stall Speed Normal But Acceleration Poor
If stall speeds are normal (1800-2300 rpm) but abnormal throttle opening is required for acceleration, or to maintain cruise speed, the converter overrunning clutch is seized. The torque converter will have to be replaced.

Converter Noise During Test
A whining noise caused by fluid flow is normal during a stall test. However, loud metallic noises indicate a damaged converter. To confirm that the noise is originating from the converter, operate the vehicle at light throttle in DRIVE and NEUTRAL on a hoist and listen for noise coming from the converter housing.