This is a discussion on 4L60e problems within the GM Trucks forums, part of the Vehicle Specific category; what is the function of the vss buffer on a 1993 s10 blazer 4l60e transmission....
07-31-2006, 11:51 AM #1
- Join Date
- Jul 2006
- union city,tn
- 2000 chevy 4X4
what is the function of the vss buffer on a 1993 s10 blazer 4l60e transmission.
07-31-2006, 02:00 PM #2
I will not take credit for this because it's a JTR copy. I think this will pretty much explain it all.
The VSS tells the ECM how fast the vehicle is going. Most people think the VSS is only used for the lock-up torque converter. The VSS is also used to control the EGR valve, the charcoal canister purge valve, the electric cooling fans, idle speed, and air/fuel ratio. the VSS is used to control the idle speed when the vehicle is moving. Without the VSS, a vehicle may have stalling problems under certain conditions. The reason an engine not equipped with a VSS may stall is because when the ECM has the signals that indicate the engine should be idling (foot off the gas pedal, vehicle moving less than 2 mph), idle speed is closed loop (which is not the same as the O2 sensor running closed loop) and the ECM will try to maintain a programmed idle speed. If the vehicle is moving (with a VSS), the ECM opens the IAC (idle air control) a programmed amount, regardless of engine speed, which is usually a position that will make the engine idle about 50-100 rpm above the stationary programmed idle speed. Stalling can occur when the vehicle is in the over-run condition (foot off the gas pedal, engine speed above the programmed idle speed) because the ECM will close the IAC to try to lower the idle speed to the stationary Programmed speed. During some overrun conditions, the fully colsed IAC may not be able to open rapidly enough to prevent the engine from stalling. Raising the minimum idle speed with the adjusting screw can eliminate stalling, but the engine will still not run optimally without a VSS. A lot of people think that running “closed loop” is best for fuel mileage. Closed loop simply means that the oxygen sensor is being used to monitor the fuel/air ratio. Some of the Chevrolet fuel-injected engines are programmed to run lean under certain conditions (called “highway mode”) to improve fuel mileage during steady cruise conditions. Without a VSS, the ECM will not get the correct signals to run the engine for best fuel mileage. There are a lot of programs in the ECM which depend on the VSS. For best operation, the Chevrolet fuel-injected engines require all sensors to be connected and functioning. There are 4 types of VSS signals required by the ECM:
1. The two-pulse (2000 pulses per mile) square wave (D.C current or direct current) used on all TBI engines thru 1992, all computer-controlled-carbureted engines, and on 1985-1989 TPI engines.
2. A four-pulse (4000 pulses per mile) sine-wave (A.C. current or alternating current) signal is required by the 1990-1993 TPI, 1992-1993 LT1 engines, and 1990-1993 Camaro 3.1/3.4 V6 engines.
3. A 40 pulse per driveshaft revolution speed sensor used on 1993 and newer trucks with automatic transmission, 1994 and newer rear drive cars with the automatic transmission.
4. A 17 tooth per driveshaft revolution speed sensor used on 1993-1997 LT1 engines with the Borg-Warner 6-speed transmission. An 11 tooth reluctor ring is used on 1993 LT1 engines with the Borg-Warner wide ratio (3.35 First gear) 6-speed transmission.
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