Frequently Asked Questions (FAQ)
What is a COMPUSHIFT?
COMPUSHIFT is a brand name of HGM Automotive Electronics family of transmission control systems.
Click here to find your transmission and be guided through to a customized kit that will be perfect for you!
How do I setup COMPUSHIFT using the App?
Setting up COMPUSHIFT using the App is a relatively simple process. Please refer to the following link to see a video here - link.
I hear a buzzing or humming sounds from the transmission with the key on and engine off. Is this normal?
This is normal and it is not a malfunction. The pressure control solenoid in some transmissions buzzes or hums. This can be especially loud when the transmission is cold or there is no oil in the transmission. Once the engine is running, this sound will be inaudible.
Can I use COMPUSHIFT transmission controllers with a diesel engine?
Yes. HGM supplies COMPUSHIFT with settings for both gas and diesel engines.
Is it safe to piggyback a throttle position sensor (TPS)?
Most engine control systems have their own throttle position sensor, and in most cases, you should use this sensor instead of installing a second one for COMPUSHIFT. Most engine control system / electronic fuel injection system makers don't recommend piggybacking sensors due to problems with ground loops and interference, but all COMPUSHIFT products are designed with a circuit called a differential amplifier that helps prevent these problems.
I’ve tried multiple times to calibrate my TPS, but the calibration doesn’t work. What now?
If your TPS won’t calibrate, it’s probably because there’s not enough voltage difference between the low and high output from your sensor. All COMPUSHIFT controllers require at least 1.25V of change across the full motion range of the TPS. You can monitor the TPS voltage and range directly during the TPS calibration process, as the low, present, and high signals are shown on the calibration screen. The voltage on the sensor can also be monitored in Voltage Diagnostics. If the sensor doesn’t change by at least 1.25V, for example from 2.00V to 3.25V, the system will not calibrate and will stay in the failsafe condition. Be sure to disable the TPS ground when you are monitoring a sensor connector to an existing engine ECU, and do not connect the +5V reference wire.
Can I connect the tachometer output from my ignition system both the tachometer input to the COMPUSHIFT transmission controller and a tachometer gauge on the dash?
Yes. This usually works just fine.
How do I get the tachometer to work on COMPUSHIFT transmission controller on a diesel engine?
Newer diesel engine control system's often have a tachometer wire, just like a gas engine. Older diesel engines sometimes have a tachometer wire that comes off the alternator. Often these are not quite the right speed, so you need a corrector to fix this. For many applications, you don't really need a tachometer input to the COMPUSHIFT system. It will usually run correctly without one, especially if the engine isn't a high performance gasoline engine.
Do I need a laptop computer to program the system?
No. All adjustments and programming to COMPUSHIFT can be done with the mobile app or the handheld display / programmer
Does the torque converter clutch (TCC) unlock during gear changes?
On most transmissions and control programs, the torque converter clutch always unlocks during downshifts, and sometimes during upshifts, depending on the vehicle speed and throttle position. It is safe to upshift under light load while the TCC is locked, and most OEM systems do so.
How do I connect an electronic speedometer to a COMPUSHIFT transmission controllers?
COMPUSHIFT controllers provide an output signal for driving most electronic speedometers, typically on a purple/white wire. This signal is usually replicates the transmission output shaft speed (TOSS) sensor signal coming from the transmission, but can be adjusted from within the app. This signal should also be used when you have an existing factory speedometer or engine control computer that uses the TOSS sensor. See Connecting COMPUSHIFT to Digital Dashes and Speedometers for more information.
How do I connect an mechanical speedometer to a COMPUSHIFT transmission controllers?
If you need to drive a mechanical speedometer, you can get a speedometer driver that will convert turn a speedometer cable based on a digital speed signal from the COMPUSHIFT controller.
Two known to work are:
How do I use an existing throttle position sensor (TPS)?
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.
How much does COMPUSHIFT cost?
COMPUSHIFT prices are set on this website and by our dealers and representatives. You may purchase HGM transmission controllers, accessories and parts from this website or contact your nearest representative. A list of dealers can be found by clicking here.
I don't understand the function of the "always upshift at" setting. What exactly does it do?
The "always upshift at" attempts to place an absolute engine RPM limit on each gear. The controller will always upshift when this engine RPM is reached. The controller measures 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 RPM limit at full throttle. You must not use this feature as a rev limiter for your engine.
I've installed COMPUSHIFT on a rebuilt GM transmission, but it doesn't shift correctly. What could be wrong?
GM transmissions originally built for four-wheel drive usage have the transmission output speed (TOSS) sensor in the transfer case. Often these transmissions are refitted with a standard output shaft snout for two-wheel drive service. Although the transmission has the hole in the side of the case for the TOSS sensor, the toothed ring gear inside of the transmission is not always there. Here's a hint. Before installing a TOSS sensor, look inside the TOSS sensor hole and be sure that you can see square lugs about 3/8" by 3/8". These are the teeth of the toothed wheel that generates the TOSS sensor signal. It should look like this:
If the surface you see inside the hole is smooth, you'll have to break down the gearbox and install the toothed wheel. Despite the work involved, is a lot better to find this out before the transmission is in the car.
My GM 4L60E / 4L80E transmission doesn't shift at all and / or the gear indicator shows "I" on screen.
Though difficult, it is possible to plug the connector to the transmission in upside down. Be sure that the white line on the plug is facing up, not down.
My GM 4L80E transmission doesn't shift at the right speed.
The 4L80E has two speed sensors, one at the front (the input shaft speed sensor), and one at the back (the output shaft speed sensor). Make sure that the COMPUSHIFT speed sensor connection is connected to the rear speed sensor, not the front one.
My COMPUSHIFT transmission controller is acting erratically. What could cause this?
Poor wiring causes many of the problems we hear about. We have seen painted bolts used as frame grounds, 18-gauge wire used for power, and rat's nests of connectors in between. The solenoids and sensors in the transmission require a few amps of clean power to run properly. Make sure that you use soldered connections wherever possible. A dedicated connection to a switched ignition circuit is recommended.
Occasionally, my COMPUSHIFT transmission controller shuts down entirely, but later restarts and works correctly. Why would it do this?
The COMPUSHIFT transmission controller is a precision piece of instrumentation designed to handle the difficult environment of a car. However, it isn't designed to run under-hood or exposed to water, and it relies on some free airflow to provide cooling to the internal components. COMPUSHIFT transmission controllers have a temperature sensor inside of the controller case and will shut down temporarily if safe operating temperatures are exceeded. Be sure to mount the controller inside the car, but away from the heater and heat from the exhaust system.
What is the difference between PWM and non-PWM torque converter clutches?
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.
How do I mount the COMPUSHIFT display in my vehicle?
The COMPUSHIFT handheld display has a 1/4-20 bolt in the back that can be used to mount the display in the same way that a camera mounts to a tripod. A good source of mounts in RAM Mounting Systems.
What is the hole size for the firewall grommet?
The proper hole size is 1 5/8" or 4.125 cm.