Q. How do I use an existing throttle position sensor?

A. Many Compushift customers are using a carbureted gasoline or diesel engine. For these applications, the throttle position sensor provided in the Compushift kit is used. But, if you use Compushift with an electronically fuel-injected engine, you can often use the existing throttle position sensor instead of the provided one.

Here’s a little explanation on how the TPS works, and how to use the existing one: A throttle position sensor usually has three wires: +5 volt power, ground, and signal. The power and ground wires supply a reference voltage to either side of a variable resistor. As the shaft rotates, the signal wire has a voltage that varies between +5 volts and ground.

In order to connect Compushift to an existing TPS, you only need to connect two wires, the ground wire and the signal wire. These can be piggybacked on top of the existing wiring using an in line wiretap, but they should be done as close as possible to the sensor. The +5 volt wire coming from the Compushift should be left disconnected, but insulated to prevent a short circuit.

Q. I don’t understand the function of the “always upshift at” setting. What exactly does it do?

A. The “always upshift at” places an absolute engine rpm limit on each gear.

The controller will always upshift when this engine rpm is reached. The controller measure engine speed from the tachometer input, if connected, or calculates engine speed based on driveshaft speed and gear ratio. The tachometer is the more accurate measurement because all torque converters slip. As the “shift speed” adjustment is increased, the transmission shifts at greater speeds for a given throttle position. The “always upshift at” provides a cap for this adjustment. This allows you to have the transmission shift at high rpm with light throttle, but still not exceed the engine’s RPM limit at full throttle.

Q. What is the difference between PWM and non-PWM torque converter clutches?

A. PWM stands for pulse width modulation. In transmission control applications, PWM is a way of controlling a solenoid so that it applies varying amounts of hydraulic pressure according to computer control. PWM torque converter clutch systems use apply and release the clutch gradually to improve shift feel.

Unfortunately, many of the PWM controlled systems cause the clutch to slip, and, over time, eventually fail. Over time, manufacturers have introduced and then later removed this gradual apply/gradual release feature.

Some types of transmissions have been built with both PWM and non-PWM versions of the converter clutch. For those transmissions, Compushift has a setup menu selection that lets you choose PWM or non-PWM.

Whether PWM or not, Compushift always does a quick apply and release of the torque converter clutch. We feel that it is more important, especially in high-horsepower applications, to preserve the life of the clutch rather than improve shift feel.

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