When we began building the Hot Rod Hauler, our updated ’73 Ford F-350, we had a number of objectives. One of the most ambitious was to increase fuel economy while maintaining towing capacity. The first modification toward that goal was the installation of an E4OD overdrive automatic transmission from Gearstar Performance Transmissions.
As we showed last month, replacing the C6 with an E4OD was not without challenges. There were some crossmember modifications required, the gas tank had to be slid back in its mounts, and the front end still required some “massaging” with a rubber mallet. However the biggest challenge was the shift linkage. It could have been done with a cable but we elected to take advantage of our friend and master machinist, Tim Smith, and build a mechanical linkage with a bellcrank.
With the mechanical part of the installation done, it was time to turn our attention to the computer and wiring harness that makes our high-tech trans work. From a functional standpoint the E40D has some unique features. As you would expect, Park, Reverse, and Neutral are standard shifter positions, but unlike many other four-speed overdrive automatics there are only three other shifter positions—D, which allows the transmission to shift through all four gears, D2 which locks the transmission in Second gear only (the vehicle starts in second and stays there), and D1, which locks the transmission in First and keeps it there. What’s missing is a Third gear position, but while it may not be on the gearshift indicator, it is available at the push of a button. Activating the “cancel switch” prevents the transmission from shifting into Fourth (however the converter will still lock).
In stock form the E4OD is controlled by a system referred to as the EEC-IV, it’s a processor that controls both the engine and transmission. What we needed was a stand-alone controller to operate just the transmission and through Gearstar we found just what we needed; the Compushift II from HGM Automotive Electronics, a specialty equipment manufacturer that designs and supplies leading edge electronic systems for automotive aftermarket use. Compushift II operates automatic shifting, paddle shifting, and torque converter clutch lockup for a wide variety of transmissions, including the E4OD.
Installing the computer and wiring harness is simple enough, however we urge you to go against the normal tendency to disregard the instruction manual and dive in. Despite the fact that all the wires are clearly labeled, all the plugs are dedicated and will only fit in the proper place. Improper installation can not only keep the transmission from operating properly, it can damage the control unit. So do yourself and the tech guys at HGM a favor and read the manual before you begin installation.
While we are on the subject of installing the HGM controller, we should touch on what can go wrong and, surprisingly, the most common problem is easy to avoid—poor grounds. After everything in your truck is painted, plated, and powdercoated, it can be tough to find a good spot to ground electrical components, but a good ground is absolutely essential to the proper operation of the HGM system (as well as every other electrical device). That’s why HGM recommends grounding their system directly to the block (but the connection point still needs to be clean, bare metal).
We began our installation by running all the wires to their various locations. The big trick here is to route them out of harm’s way, avoiding things like the exhaust system and sharp edges that can damage wire. With the harness installed, the next chore was to find a place to mount the control unit inside the cab.
The next step was attaching the throttle position sensor to the carburetor. For carbureted engines HGM offers their AccuLink kit to mount a TPS on virtually any carburetor. For those engines that are fuel injected, the existing TPS can be used to supply the transmission computer the necessary signal.
One technician from start to finish builds Gearstar transmissions. We’ve used and abused a
Gearstar offers a variety of transmissions to suit any application from street to race and
Modern electronic transmissions are “brain dead” without a computer, we used a Compushift
The available Compushift display is used to program the TPS and other functions. It can al
The control box has dedicated plugs for the engine and input power and ground on one end.
On the other end are the plugs for the transmission harness and the display unit.
So air could circulate around the control unit we mounted it to the inside of the firewall
To mount the control unit securely threaded inserts were put into the firewall.
Space is at a premium under the dash, so the control unit was mounted to the left of the s
HGM recommends that the control unit be on a dedicated electrical circuit. As we would be
This is the optional Fourth gear lockout button; it connects to the HGM harness. Not neces
This is the AccuLink TPS control kit, we installed it on our Edelbrock carburetor. When we
With the installation complete it was time to do what we feared most, the electronic wizardry that’s normally the domain of 12-year-olds—programming. Fortunately for most of us, a PC, laptop, or other type of computer isn’t needed as the system is delivered with factory set programming; however a PC can be connected via the USB port for system software updates and tuning if desired. Dual CAN buses can connect to existing engine management or body control computers. A MAP sensor can be connected for turbocharged applications if needed.
For the system to operate, the TPS has to be calibrated. Start the engine and allow it to warm up enough so it’s no longer on fast idle or choke. Then turn the engine off.
With the vehicle in park and engine off, turn on the ignition switch to provide power to your Compushift II. Wait five seconds.
Enter setup mode on the display and press the right arrow (next screen), the TPS Calibration Setup screen is visible.
Press the enter button and you’ll have five seconds to completely depress and release the throttle pedal. This one stroke of the throttle pedal should be done in a slow, even motion before the five seconds elapse.
Once you’ve stroked the throttle, wait five more seconds, and then observe the status LED on the Compushift II Controller—it should be green and solidly lit (not blinking).
Depress the throttle pedal completely and hold it for five seconds. The LED should still be green and solidly lit.
With the TPS calibrated, all that was left was to take the truck for a drive. Under light throttle the Gearstar E4OD shifted quickly and smoothly, but when we stuck our foot in it, the shifts were later and much firmer. We found the gear ratios are ideally suited to our needs but the biggest difference was the overdrive top gear and the lockup converter; at highway speeds the reduced rpm has made a noticeable reduction of engine noise in the cab and throttle response without the slippage of a standard converter is noticeably improved. Although we haven’t had the opportunity to compare mileage, we’re hopeful and will report soon. Stick around, there’s more Hot Rod Hauler to come. CCT
Q. Do I have to purchase the display/programmer in order to correctly install Compushift?
A. No. Your dealer/reseller can send you a controller pre-programmed with most of the needed settings. Throttle calibration and shift point/shift pressure adjustment can be done without the display. The display does offer the greatest flexibility in setup, though. It can also serve as a “digital dashboard”, providing you with running information about vehicle and transmission performance.
Q. Do I need a laptop computer to program the system?
A. No. All adjustments and programming to Compushift can be done with the handheld display/programmer.
Q. Does the torque converter clutch (TCC) unlock during gear changes?
A. 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.
Q. How do I run a speedometer with Compushift?
A. Compushift provides an output signal for driving speedometers. This signal is called reproduced TOSS. This signal replicates the signal coming from the TOSS (transmission output shaft speed) sensor.
This signal should be used when you have an existing OEM speedometer or engine control computer that uses the TOSS sensor. Reproduced TOSS comes off of the 25-pin connector and comes with enough cable to connect back to an original TOSS plug.
A device called the Cable-X can drive mechanical speedometers if necessary. Built by Abbott Enterprises, the small Cable-X box motor rotates a speedometer cable at a rate proportional to an electronic speed input, and is calibrated to match your speedometer using internal switches. HGM is an authorized Cable-X reseller.
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.