XT-6 2WD L6-2.7L SOHC (1989)
Continuously Variable Transmission/Transaxle: Technical Service Bulletins
A/T - Engine Vacuum Testing
BULLETIN: # 028
DATE: October 1990
SUBJECT: Engine Testing With A Vacuum Gauge
TRANSMISSION: All
Engine Testing With A Vacuum Gauge
ENGINE/TRANSMISSION RELATIONS
An important part of transmission diagnosis is to make certain the engine operates properly. If the engine performance is incorrect, the transmission will
receive the wrong information.
The engine sends signals to the transmission through a vacuum line, throttle cable or both. These signals basically synchronize torque with transmission
line pressure, shift feel and shift timing.
Malfunctions in items like the air filter, spark plugs, EGR valves and other parts of the fuel, electrical and emission systems could result in improper
transmission performance.
VACUUM GAUGE ENGINE PERFORMANCE TESTING
A vacuum gauge shows the difference between outside atmospheric pressure and the amount of vacuum present in the intake manifold.
The pistons in the engine serve as suction pumps and the amount of vacuum they create is affected by the related actions of:
^
Piston rings
^
Valves
^
Ignition system
^
Fuel control system
^
Other parts affecting the combustion process (emission devices, etc.).
Each has a characteristic effect on vacuum and you judge their performance by watching variations from normal.
It is important to judge engine performance by the general location and action of the needle on a vacuum gauge, rather than just by a vacuum reading.
Gauge readings which may be found are as follows:
NORMAL ENGINE OPERATION
At idling speed, an engine at sea level should show a steady vacuum reading between 14" and 22" HG. A quick opening and closing of the throttle
should cause vacuum to drop below 5" then rebound to 23" or more. See figure 1.
GENERAL IGNITION TROUBLES OR STICKING VALVES
