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Subaru Impreza 2.5RS Part XI

Part XI: Wiring the Tec-II

Shiv S. Pathak
Dec 12, 2002
0010scc_subaru_01 Photo 1/19   |   Snuggled in some AC lines and wrapped with a strip of silicone, our boost control solenoid takes the place of the HKS EVC IV. While our little solenoid is not as impressive-looking as the HKS solenoid box, once tuned, it should work just as well.

How'd We Get Here?

With a lot of luck, that's how. We mention luck because we've somehow managed to eke out an estimated (and arguably reliable) 300 turbocharged hp with stock fuel injectors, stock ignition system, an array of vague piggy-back devices and fuel pressure risers. Fortunately, all of that is going to end. Right now. It's time to get off the ragged edge and do things the right way. And this will involve going back to square one.

Out With the Old...
Relying on several piggy-back computers to keep our engine running safely does have its share of down sides. Besides the limited tunability offered by these popular electronic gizmos, another problems is only seen upon investigation of the stock ECU harness. Not only is such a sight an assault to our aesthetic senses, it is also a sure fire cause of future reliability issues. With several single points of system failure, each hanging its fate on the integrity of a crimped wire, plastic splice, bullet connector or fragile solder joint, it's only a matter of time before we find ourselves stranded on the side of the road, holding a flashlight in our mouths, poking, prodding and testing each connection, trying to revive our street monster.

0010scc_subaru_02 Photo 2/19   |   Unlike many other programmable EFI systems, the TEC-II has built-in adaptive knock sensor capabilites. We're quite certain that we'll be needing it.

The solution? Get rid of all those piggy-back computers and install a fully programmable engine management system--something we've been looking forward to for quite some time. Not only would doing this yield a significant performance improvement, it would also greatly reduce the likelihood of spontaneous system failure, while easing the burden of troubleshooting. After all, it's far easy to diagnose one system than several systems working interdependantly of one another. In this installment of Project Impreza, we are going to document the work involved in installing such a stand-alone system. But with one catch--it's not going to be stand-alone. Read on.


0010scc_subaru_03 Photo 3/19   |   With our custom spacers, the fuel rail is held securely with no weird angular loads acting upon our larger-than-stock injectors. Leaving the stock injector harness intact allows us to revert back to stock injectors and engine management with little effort. It's as simple as swapping in the old injectors and plugging in the connectors.

...And in With the New
In an effort to prove wrong all of those pessimists who insist that the installation of a programmable engine management system is a long and tedious process, full of glitches and unexpected incompatibilities, we've put together an easy-to-follow installation guide, using the ever-popular Electromotive TEC-II engine computer, that any shade-tree mechanic should be able to follow. What makes our installation technique so special? It's called Parallel Engine Management (PEM, for short) and it redefines the role of the traditional programmable EFI system.

Historically, these systems were sold as stand-alone devices. That is, unlike inexpensive piggy-back controllers, they replace the entire stock engine control unit (ECU), taking over all functions, engine-related and otherwise. Typically, this approach has involved a few complications. Namely, the carbon canister purge, fuel pump relay, engine fans, tachometer, idle control and air conditioning systems often had to be rewired, reconfigured or reprogrammed in order to maintain stock-like functionality. Not exactly plug-and-play.

0010scc_subaru_04 Photo 4/19   |   Can you guess which injector flows more fuel?

The patent-pending PEM system, as developed by Vishnu Performance Systems, approaches this dilemma from another angle, posing the question, "Why can't the aftermarket programmable EFI system run in parallel with the stock engine computer?" Not only would this facilitate installation by allowing the stock computer to retain tachometer, fuel pump, engine fan, idle control functionality, it would also keep all secondary subsystems and emission control devices intact and functional. With the programmable EFI system only controlling combustions and with the stock ECU dealing with everything else, we would have the best of all worlds--maximum performance, ease of installation and full functionality. There are a few secondary benefits as well. One, by virtue of inherent redundancy, is the ability to easily revert back to stock ECU control in the (albeit unlikely) event of the aftermarket EFI system failing. Another benefit is no longer having to bury the aftermarket computer--wiring harnesses and all--into the stock ECU provisions. In other words, no gratuitous wire hacking. In fact, the entire installation, as directed by Vishnu Performance Systems, involves the cutting of just one factory wire--and even that is optional!

Mounting the TEC-II
As with most modern cars, the engine bay in our turbocharged Subaru Impreza is tightly packaged--not leaving much place for an oil catch can, let alone something the size and shape of an Electromotive TEC-II engine computer.

0010scc_subaru_05 Photo 5/19   |   While serial ports aren't exactly known for their blazing data transfer speeds, we will only use it for program loading purposes and to transfer engine monitoring data from the TEC-II computer to our little laptop.

Perhaps the only empty spot of sufficient size, was the area formerly occupied by the BEGI rising rate fuel pressure regulator (on the rear firewall, just above the brake booster). While this location would have ensured good water protection and sub-200 degree F underhood temperatures, we had other, slightly more industrious plans in mind. Namely, the construction of an all-aluminum, fully enclosed, dual-filter, cold-air intake box.

Not only would this imaginary intake system be able to efficiently support the prodigious airflows our turbo engine is currently generating, it would also prove to be the ideal spot in which to mount the TEC-II unit--away from heat, water, and perhaps most importantly, prying eyes. But as with most good ideas, we thought of it a bit too late. And deadlines being what they are, we were forced to abide to the rules of a higher power. We'll have to make do with what we have now, relocating the TEC-II later. With this in mind, it would make sense to abstain from final wire trimming and other non-reversible tweaks until the TEC-II is situated in its final location.

0010scc_subaru_06 Photo 6/19   |   Since there is less than an inch of plumbing between the cold side of the intercooler and the intake manifold, this seemed like the most logical placement. Removing the manifold to drill and tap for this fitting would be more work and get the same results.

But for now, we're going to temporarily mount the TEC-II on the inner fender, just behind the driver's side headlamps. By now, you're probably thinking, "Hey, doesn't a big fat battery sit in that very same spot?" Not any more. You see, big fat batteries have no place in high-performance vehicles. Especially in light of the advances made by Hawker Energy in dry cell battery technology.

Weighing only 15 lbs and capable of spitting out 280 cold cranking amps, the super slim Hawker Genesis dry cell battery is well suited for our space and weight saving needs. Displacing only 126 cubic inches (7x3x6), we mounted the battery flat in the stock battery's plastic pan, freeing up just enough room to bolt the TEC-II to the inner fender. Eventually, we plan to relocate the battery into either the trunk or under the passenger seat. But that job, like our imaginary airbox installation, is postponed for another day. Right now, let's get on with our TEC-II project.

0010scc_subaru_07 Photo 7/19   |   The intake temperature sensor needs to be mounted where it can measure the temperature in the intake manifold.

Powers and Grounds
With power coils and beefy injector drivers, the TEC-II is a high-ouput device. Now, imagine all this active juice next to sensors that are measuring wee millivolts. Immediately, it becomes clear that the TEC-II's power and ground singals must be configured so that voltage spikes simply don't occur. As suggested by Electromotive, we routed the power wire directly to the positive battery terminal (which we disconnected for now, of course) and the black wire to a bolt on the engine block.

Inputs
As with any computer, automotive or otherwise, you need to feed it inputs before it can do anything useful on the output end. In the case of engine management, without knowing engine speed, load, throttle position and gobs of other data, the TEC-II won't be able to deliver the correct amount of fuel or a properly timed spark. In other words, it's about as useful as a pretty paperweight.

0010scc_subaru_08 Photo 8/19   |   Ah, the mysterious connector! While we aren't quite sure what it's for, we know that we are not using it for anything. Filled with creamy gunk, things can get a little messy when testing for ignition switched 12 volts.

First up for discussion is the the coolant temp sensor, or CLT as designated on the TEC-II unit. A coolant temp sensor is used by the TEC-II to measure, you guessed it... coolant temperature. As with almost all temperature sensors, the coolant sensor provides electrical resistance which varies with sensor temperature. At a mild 70 degrees F, the coolant sensor provides approximately 2.8k ohms of resistance. As temperature goes up, resistance goes down, increasing the voltage going back to the TEC-II. In order to get a temperature reading, the TEC-II sends 5 volts of juice downstream and sees how much of it comes back home. Pretty simple stuff.

Typical installation would involve screwing the sensor into the engine water jacket, right before the water enters the radiator. While such a location provides the most accurate reading of actual coolant temperature, we can get by with a much simpler solution. Instead of tapping a 3/8-inch NPT hole into our block, let's just tee the sensor into one of our heater core lines. Before you scoff at our shortcut, let's remember that since we are running the TEC-II in parallel with the stock ECU, we're only using this coolant temperature sensor input for cold start fuel enrichment purposes. The stock coolant sensor, which is located in the engine block (as we would expect!) still controls all the important stuff like the engine fans and the water temperature gauge. To install, we clamped 4-inches of 2 5/8-inch heater hose on the tip of the sensor, crammed a heater hose tee on the other end, and stuck it in the middle of the lower rear heater hose. On the TEC-II side, we routed the white wire to Input Pin 1 (CLT) and the black wire to Input Pin 2 (S GRD).

0010scc_subaru_09 Photo 9/19   |   Compared to the stocker, the oxygen sensor supplied with the TEC-II kit has an extra ground for the signal. Although we have not quantified its effects, the separate ground should reduce signal degradation.

MAP Sensor
Designed to be a speed density system, the TEC-II relies on a Manifold Absolute Pressure (MAP) sensor for all of its fuel and ignition calculations. Unlike our stock mass airflow meter, which measures actual airflow (when it's not blown, that is), the MAP sensor reads engine load. Just a fancy word for manifold pressure, load is typically displayed in either kiloPascals (kPA) or inches of mercury. Now, here comes the fun part: 100 kPa is equal to 1 Bar which is equal to one standard sea level atmosphere. The intake manifold of a naturally aspirated engine, at wide-open throttle, should see something pretty darn close to this value. A turbo or supercharged engine, however, will see much higher loads. With 14.7 pounds (or 1 bar or 100kPa) of boost, the manifold will see approximately 200kPa of absolute manifold pressure. Remember that a base atmospheric pressure of 100kPa plus 100kPa of boost pressure equals 200kPa of absolute manifold pressure. But not all MAP sensors are created equal. In fact, we have to choose between a 1-, 2- or 3-Bar unit. Since we don't plan on running more than 1-Bar of boost in the future, we chose to use the 2-Bar MAP sensor.

To install, we bolted the MAP sensor down to the fuel rail bracket and ran a short, uninterrupted vacuum line from the sensor nipple to the nipple right on top of the intake manifold plenum. Never plumb the MAP sensor into an individual intake running as the undamped pressure pulses will disrupt fuel calculations. Also, Electromotive suggests that the vacuum line be as short as possible for maximum accuracy. As for wiring, the black wire goes to Input Pin 2 (S GRD), the white wires goes to Input Pin 3 (MAP), and the red wires goes to Input Pin 4 (+5V).

0010scc_subaru_10 Photo 10/19   |   Care must be given to ensure the TEC-II is referenced off the correct tooth. A one tooth aberration will result in six degrees of mechanically induced ignition retard or advance.

Throttle Position Sensor
Next up is the throttle position sensor which is basically a variable potentiometer generating an output ranging from 0 to 5 volts. The greater the throttle angle, the greater the voltage. This sensor is used by the TEC-II to anticipate, among other things, sudden changes in engine load, followed by rapid accelerations or decelerations. Instead of installing a new sensor, we're simply going to splice into the signal output wire (the solid yellow wire) of the stock throttle positions sensor connector. Our piggy-back TPS signal wire is routed to Input Pin 5 (TPS).

Magnetic Pick-up Assembly/Crank Trigger
Perhaps the most distinguishing feature of the Electromotive TEC-II is its crank-triggered ignition system. Instead of relying on our low resolution stock camshaft angle sensor to provide the engine computer with engine speed and crank angle data, the TEC-II literally "cuts out the middleman," eliminating backlash and mechanical slop by gathering all of its ignition information right from the crankshaft. With no chance of timing belt stretch, camshaft twist or extraneous free-play, the TEC-II receives near-perfect ignition information which is then processed by proprietary HREIC (High Resolution Electronic Ignition Chip) integrated circuit.

0010scc_subaru_11 Photo 11/19   |   Fabricating an effective mount for the crank sensor pickup seems like so much trouble for something so small. But it is well worth the effort.

Using this separate, highly specialized CMOS chip for all ignition-related computing functions relieves the TEC-II's main processor of a great deal of computational overhead. This unique parallel feature, combined with the ultra-stable data stream provided by the crank-trigger, allows the TEC-II's 8-bit main processor to perform computation tasks faster and more accurately than many higher-powered and far more expensive 32-bit engine control systems. For our internally stock, high-compression, high-horsepower engine, we need all the ignition accuracy and computational speed we can get!

As always, doing things right requires some work. In our case, we had to mount a toothed wheel to our stock crank pulley and fabricate a magnetic sensor bracket. Fortunately for us, the engineers at Subaru left just enough clearance behind the crank pulley for us to mount a slim 0.125-inch thick toothed trigger wheel. Available from Electromotive in a variety of diameters, we chose to go with a 6-inch trigger wheel. With the help of our local machine shop, we bored open the wheel's center hole. Then we mounted it to the back of our stock pulley with four recessed bolts. Next, using a lathe, we made sure the entire assembly was no more than 0.002-inch out-of-round. With the pulley assembly completed, we could reinstall it back on our car.

0010scc_subaru_13 Photo 12/19   |   Before...

Of course, our machine shop experience didn't end there. We still had to fabricate a device that would hold our magnetic pick-up securely in place. Not just any place, mind you. With cylinder one rotated to Top Dead Center (TDC), we had to reference our magnetic pick-up off the eleventh tooth (counting clockwise from the two missing teeth). Making things more challenging, our magnetic sensor had to be air-gapped to the trigger wheel teeth by a scant 0.045 inches--not much wider than a standard spark plug gap! This would necessitate a rigid and stable pick-up bracket.

After countless hours of measuring, test-fitting, prototyping and revising, we finally came up with just what the doctor ordered--a two-piece billet aluminum bracket that bolts to both the lower power steering bracket as well as an adjacent plastic engine cover mount. We've also engineered in quite a bit of swivel adjustability in both the main bracket and the smaller magnetic pick-up holder to account for unforeseen variances or miscellaneous clearance issues. Once bolted on the block and properly adjusted with the correct magnetic pick-up air gap, we tightened the entire assembly, using a little bit of thread locking compound for extra insurance. We ran the magnetic pick-up cable under the alternator, beneath the intake manifold and towards the TEC-II computer. We routed the black wires to Input Pin 6 (GND), the red wire to Input Pin 7 (MAG PU) and the bare wire to Input Pin 8 (SHEILD).

0010scc_subaru_12 Photo 13/19   |   ...And after! Notice the two missing teeth on the wheel. This gap is used by the TEC-II for syncronizing purposes. Without it, the TEC-II couldn't keep track of crank position or engine phase.

Oxygen Sensor
Next, we installed a heated four-wire oxygen sensor, directly replacing the stock three-wire oxygen sensor which is mounted upstream the catalytic converter. This sensor, which is found on all modern street cars, is necessary for proper closed loop feedback fuel control. By constantly monitoring oxygen content in the exhaust, this useful little sensor provides an output signal (0 to 1 volt) which is used to determine whether the engine is running grossly lean or rich. Reacting to the signal, the engine computer applies the necessary fuel correction.

Once installed, we carefully routed its wiring harness back to the TEC unit, keeping it away from the hot exhaust system with a few well-placed tie wraps. The gray wires goes to Input Pin 9 (EGO-) and the black wires goes to Input Pin 10 (EGO+). The other two wires never make it all the way to the TEC unit. Instead, they split off early and are routed towards the windshield waster bottle. One wire is grounded to one of the screws that holds the washer bottle in place while the other wire is terminated with a male spade connector and poked into an unused female connector which provides an ignition switched 12 volts of juice. Coincidentally, this male spade termination is also shared with one of the wires coming out of our nifty little boost control solenoid. But more on that later.

0010scc_subaru_14 Photo 14/19   |   Far more benign than clipping, twisting and soldering, a well-placed splice gets the job done. For those less concerned with reversibility, the clipping, twisting and soldering method is suggested.

Intake Temperature Sensor
Often overlooked but always important, the intake temperature sensor is absolutely vital for maximum performance. With intake temperatures varying between ambient and 70 degrees F above ambient, the computer must be able to automatically acount for changes in air density. Without this sensor, a speed density system would have to rely on closed loop O2 feedback for final fuel trimming.

There is one serious problem with this approach. Transient misfueling due to the time it takes for the closed-loop feedback system to zero-in on the desired air/fuel ratio targets. Not only does the intake temperature sensor assist in ensuring proper fuel delivery, it can also be used--as in the case with the TEC-II--for ignition control. It should come as no surprise to our readers that engines tend to ping more as intake temperature go up. So, it only makes sense to offer a temperature-dependant ignition retard feature. One that retards ignition timing as intake temperatures increase. This feature alone should go a long away in maximizing the lifespan of our internally stock, high-compression, high-output, turbo motor.

To install the intake temperature sensor, we drilled a hole and installed the 3/8-inch NPT sensor in the bottom of the intercooler, in the lower end tank, next to the throttle body opening. Once secure, we routed the gray wire to Input Pin 11 (MAT) and the black wire to Input Pin 12 (GND).

0010scc_subaru_15 Photo 15/19   |   A perfect fit. Although placement of the MAP sensor isn't critical, it is important to keep the signal line as short as possible. Make it too long and sensor accuracy and response time can suffer.

Communication Cable
With the sensor's wiring finally completed, the only thing left to install on the input side of the TEC-II is the PC serial port communication cable. After drawing the cable though a grommet in the firewall, we routed the black wire to Input Pin 12 (GND), white wire to Input Pin 13 (TXT) and the red wire to Input Pin 14 (RXD). In our next installment, we'll actually use this thing.

Outputs
As we are about to see, operating our TEC-II in parallel with the still-functioning stock computer greatly simplifies the installation process. With the stock computer still maintaining fuel pump relay, idle control and tachometer display functions, Output Pins 1, 2, 3, 4, 5 and 7 go unused. The only Output Pins that we will use will be for the fuel injectors (Pins 11, 13, and 14), knock sensor (Pin 10), switched battery (Pin 9), check engine light (Pin 8) and boost control solenoid (Pin 6). Let's get started...

0010scc_subaru_16 Photo 16/19   |   Now standard on the 2000 Impreza, the MAP sensor replaces that annoyingly fragile contraption we call a mass airflow sensor.

Fuel Injectors
Perhaps the greatest single advantage of programmable engine management is the ability replace all those messy fuel pressure regulators and additional add-on fuel control with monstrous fuel injectors. But how big do we want to go? If we don't go big enough, we'll be back where to we started--with not enough fuel. But if we go too big we may run into some low speed/idle problems with the injectors delivering too much fuel at low load conditions such as idle and cruise. Fortunately, unlike the stock Subaru EFI system, the TEC-II is capable of driving low-impedance (also known as peak-and-hold) fuel injectors.

Compared with standard saturated injectors, which pose a 12 to 16 ohm impedance, low-resistance injectors are rated at only 2.5 to 3 ohms. This lower impedance means that less voltage is required to drive the injector. And as long as the injector driver can supply the necessary current, minimum controllable injector on-time drops from the typical 1.8-2.0 milliseconds to just 0.9 to 1.2 milliseconds. This means that, compared with the stock ECU, the TEC-II can drive significantly larger injectors before running into those irritating drivability and idling problems. It should be pointed out that some "plug-in" ECU systems are designed to use the stock injector driver circuitry. With these systems, additional in-line ballasts are required in order to run low-resistance injectors. In essence, these ballasts convert low-resistance injectors into high-resistance injectors--defeating the purpose of running low-resistance injectors altogether!

0010scc_subaru_17 Photo 17/19   |   Our coolant temperature sensor was mounted in this tee in the heater hose. Thinking it would suck if the tee came loose and dumped all our coolant on to the ground, we used the nicest, fattest, hose clamps we could find. While this may not be the ideal spot for coolant temperature measurement, it's more than sufficient for our parallel engine managed needs.

To find our much needed fuel injectors, we approached fuel injector guru Russ Collins of RC Engineering. After scrutinizing our stock fuel rail for a few moments, Collins discovered all that was needed to fit the physically larger Lucas-style fuel injectors in the stock fuel rail were a set of custom-cut spacers, which he graciously machined for us. With a short term horsepower goal of 350 hp, Collins recommended a quad set of low-resistance 550cc/min injectors--nearly twice the size of stock! With a whopping 2.5 liters of fuel-consuming displacement and the ability to control teeny, tiny injector on-times, we expected no drivability problem ahead of us. To ensure properly matched flow characteristics, Collins plopped each injector in to his custom-designed-and-built, computer-controlled injector flow-testing machine. With essentially zero injector flow variance, we were well on our way to making big, reliable horsepower numbers.

Unlike the other work we've done up to now, swapping out fuel injectors can get a little messy if a few precautions aren't taken. To ensure the fuel lines were not pressurized, we let the car sit for an hour. With fuel rail pressure minimized, we reduce the risk of squirting several stinky cubic centimeters of gasoline in our faces.

0010scc_subaru_18 Photo 18/19   |   Engine compartment room is sparse in our turbocharged monster these days, but the TEC-II had to go somewhere. The battery seemed to be the only thing that wasn't using its space efficiently, so we replaced the clunky stock battery with a Hawker Genesis dry cell to make room. As tested in the Jan. 2000 installment of Project RX-7, the little Hawker Genesis can be mounted in any position without the risk of leaking. For now, we'll just mount it in the stock battery provision. Later, we will relocate the battery elsewhere.

To pull out the stock injectors, we removed the four bolts (two on each side) that held fuel rail in place. It should be noted that in order to remove the injector to cylinder number four, we had to temporarily remove a metal brace that bolted on to the driver's side intake manifold. Then, with the rails tweaked away from the manifold, we unclipped the injector electrical connectors, and gently wiggled the injectors free. Installing the big RC Engineering injectors took a little more effort by virtue of their sheer size. To ensure proper injector seating, we lubricated each of the eight rubber O-rings with a touch of motor oil. Once finally in place, we sandwiched our custom spacers between the intake manifold and the fuel rail. With four long bolts firmly holding our new injectors and taller-than-stock fuel rail in place, we powered on the ignition and checked for leaks. All clear.

And now for the fun part--building our own injector harness. What we needed: RC Engineering injector clips, lots of 16 gauge wire, a roll of solder, a soldering iron, shrink wrap, wire strippers and a heat gun. Before we build our harness, we need to know more about the EJ25. Specifically, we need to know its cylinder firing order. A quick look at the shop manual reveals that it is 1-3-2-4. This order describes the sequence of combustion though a full 720 degrees of crankshaft rotation.

0010scc_subaru_19 Photo 19/19   |   You're looking as if you've never seen a coolant temperature sensor before.

Digging a little deeper, we see that piston 1 and 2 approach Top Dead Center (TDC) at the same time, the only difference being that one piston is on its compression stroke while the other is on the exhaust stroke. The same relationship goes for piston 3 and 4. Operating phase sequentially, the TEC-II fires both fuel and spark as a pairs of pistons approach TDC. In the case of the piston on the compression stroke, the spark and fuel combine to make combustion. In the case of the other exhaust stroking piston, the spark fires uselessly (the air/fuel mixture has already ignited) while the atomized squirt of fuel smacks against the back of the closed intake valve. Here, the fuel stays atomized (That valve is really hot!), waiting for the upcoming valve opening to get into the cylinder with yet another accompanying fuel squirt.

According to Electromotive, squirting fuel twice for each combustion event has some distinct advantages. For one, the first squirt keeps the intake valve relatively cool. Second, two squirts provide better atomization (and more complete combustion) than just one. The downside, however, can be increased tailpipe emissions when the intake valves are cold (i.e. during cold start).

Since we now know cylinders 1 and 2 reach TDC at the same time, and the TEC-II operates phase sequentially, we also know they should receive spark and fuel from the same coil and injector driver. The same goes for cylinder pair 3 and 4. Arbitrarily, let's put cylinders 1 and 2 into Group B and cylinders 3 and 4 into Group A. Group A and Group B will get their signals from Output Pin 11 (Inj. A) and Output Pin 13 (Inj. B), respectively. Since each injector requires a ground as one of its two inputs, we will daisy-chain all grounds together and route them to Output Pin 14 (COM). A few burnt fingertips later and our custom injector harness was complete. Pretty easy, huh?

Knock Sensor
OK, finally something that doesn't require soldering, excessive brain work or extraneous machining. Oh, wait a sec...two out of three ain't bad. After realizing that a) the GM knock sensor screws into the block with a 3/8-inch NPT thread and b) every bolt hole on our block uses metric thread, we discovered that we had to pay another visit to our friends at the machine shop. A few hours later, we were given a handsome steel 3/8-inch thread adapter. Then, we unscrewed the driver's side front engine mount bolt and screwed the adapter in its place. Once the adapter was installed and torqued to 50 ft-lbs, we carefully bolted in the knock sensor, torquing it to just 15 ft-lbs. We ran the knock sensor wire to Output Pin 10 (KNK).

Switched Battery
As we know by now, the the fat red power wire from the TEC-II is wired directly to the car battery. This would suggest the TEC-II is a constant current draw. Fortunately, it's not. In fact, the TEC-II is switched on only with the ignition. To do this, the TEC-II needs to see ignition switched 12 volt power. We found this signal from one of the wires (the solid yellow wire, to be exact) feeding the four-wire electrical connector that clips into the stock coil pack. Using a simple splice, we routed this signal back to Output Pin 9 (SW BAT).

Check Engine Light
Like the stock engine computer, the TEC-II comes equipped with a check engine/diagnostic light output which is triggered in the unlikely case of sensor failure. Of course, what good is a light output without a light bulb? With this in mind, we have two alternatives--to reuse the stock, dash-mounted check engine light or to install another light bulb and mount it somewhere on the dash. After a little thought, we realized that with the stock oxygen sensor disconnected, the stock computer is bound to trigger a sensor fault. This means that the stock Check Engine light will be perpetually lit or blinking, both of which would be extremely annoying. That is, unless we clip the CE signal wire (at the stock ECU harness) and reroute it to the Output Pin 8 (CK ENG) on the TEC-II. And that's exactly what we did.

General Purpose Output
The TEC-II is equipped with an extra output which can be defined to control one of many power accessories, such as a boost control solenoid, nitrous oxide solenoid, shift light, VTEC controller, intercooler water spray, etc. First of all, nitrous is for sissies. Second, shift lights are for weenies. And third, VTEC is for Hondas. And fourth, while an intercooler water spray would be nice, it would be a waste to devote a fully programmable three dimensional map output to trigger something so mundane as a pressure-activated water spray. We want boost control. With complete boost control, we could dial-in rpm-specific boost levels as well as load-specific spool-up rates. As peak boost levels increase toward the point of impending drivetrain destruction, this welcome feature could go a long way in prolonging the life of our stock transmission by lessening sudden shock loads and dampening out torque spikes.

To convert our little solenoid into a full fledged boost control valve, we need a few accessories: a strategically restricted brass tee, a brass barb fitting and a foot or so of vacuum hose. The first step was to place the brass tee into the wastegate signal line with the restricted "leg" pointing toward the turbo's compressor outlet.

Doing this effectively reduced the boost signal, giving the tiny solenoid more authority in the wastegate signal manipulation game. Next, we routed a vacuum line between the remaining tee output and the barb-equipped boost control solenoid, which we temporarily mounted near some AC lines just aft of the passenger side strut tower. Since we wouldn't want any wastegate lines popping off on us, we secured the vacuum lines with little hose clamps. Special care was also given to keep the wastegate signal line from coming into contact with the scorching hot exhaust down-pipe. With the plumbing complete, we lengthened both of the solenoid wires and routed one to Output Pin 6 (GPO) and the ignition switched 12 volt output of that mysterious little connector near the windshield washer fluid bottle.

Ignition Wires
Since the TEC-II comes equipped with its own ignition coils and since we couldn't mount it in the same location as the stock ignition coils, we need new custom-length ignition wires if we're ever going to get the car running. Historically, Electromotive ignition systems have been known to be quite critical of ignition wire selection. Many have found that, because of the TEC-II's high-output coils, a wire with proper EMI suppression is necessary in order to prevent any number of strange automotive phenomena, ranging from radio station hum to intermittent engine management glitches.

One brand of wire which we have always found to work well with these ignition systems is the KV85 Racing Wires from Magnecor. Constructed of a 2.5mm metallic inducted conductor and a generous insulating jacket made from aerospace silicon rubber, the KV85 ignition wires are designed to withstand the harshest of operating conditions. Following our fuel injector harness methodology, we routed the ignition wires for cylinders 1 and 2 to coil B and the wires for cylinders 3 and 4 to Coil A. Now would also be a good time to remove the stock ignition coils that are mounted on the intake manifold. For now, we'll keep them in the trunk--just in case we encounter any unexpected teething pains during our maiden voyage.

OK... So It Wasn't That Easy
But that's only because we had to design and machine a low-tolerance crank trigger assembly, machine a knock sensor adapater, make some fuel rail spacers, order custom-cut ignition wires and fashion a supplementary fuel injector harness. Fortunately, all of our work was not done in vain. At the time of this writing, a comprehensive Subaru-specific TEC-II is offered by Vishnu Performance Systems. Containing all of these custom components, its system should be as close to bolt-on as one could reasonably expect from an aftermarket engine computer system.

The Moment Of Truth...
With the installation now complete, we can move on to the fun part: Tuning. However, we'll leave that subject for our next Project Impreza installment. Still, a few questions remain: Will the car actually start? Are we literate enough to take advantage of Electromotive's fancy new software? If so, how much more performance can we eke out of our turbocharged Porsche-killer? Stay tune for all of these answers and more...

Sources

Electromotive, Inc.
9131 Centreville Road
Manassas, Virginia 20110
(703) 331-0100 (TEL)
(703) 331-0161 (FAX)
www.electromotive-inc.com

Magnecor
3285 Martin Road 101
Walled Lake, Michigan 48390
(248) 669-6688 (TEL)
(248) 669-2994 (FAX)
www.Magnecor.com

RC Engineering
1728 Border Ave
Torrance, CA. 90501
(310) 320-2277 (TEL)
www.rceng.com

Vishnu Performance Systems
713 Liquidamber Place
Danville, CA 94506
(925) 648-9255 (TEL)
www.vishnuperformance.com

By Shiv S. Pathak
17 Articles

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