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Tech Tips

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What to know before you jump into an Engine Management system

Our customers are having great results with the TEC-3r engine management system. Occasionally an installation will have complications. Every application is different. With ANY aftermarket Engine Management system there is a chance that the engine may not function properly when installed. Only rarely is the engine management itself actually part of the problem. The few installations that everyone hears about on web forums and elsewhere are typically from people convinced that they did everything correctly and the problem has to be the ECU. In our experience, the causes for these problems show up after some investigation and are almost always wiring related.

Wiring an Engine Management system

There are many opportunities for wiring issues to arise. If the ECU receives false or inconsistent information from the sensors, the engine will run based on false information. False information at the ECU will result in a poor running or gremlin infested engine. There is lot of assumed wiring knowledge by the engine management manufacturers. Some manufacturers require their dealers to go through training for installing, wiring and tuning. For the novice this lack of training can be a pitfall in the project. Our best advice is be careful, neat, and follow the list of wiring tips below when installing an engine management system. When you buy a system from us, we are available for technical support during and after the system installation. If there are issues after the system is installed, we work with you to find the problem and correct it.

We have compiled this list of tips to eliminate the most common forms of wiring problems when installing an engine management system.


Route the wire harness away from devices that make electrical noise, such as spark plug cables, starter motor, alternator, electric fans and pumps. This applies especially to the crank sensor cable. The induced electrical noise from these devices can cause false signals.

Wiring Tip #2 - HARNESSES

Wire harnesses are often built in bundles. Wrapping all the wires in one bundle can induce noise within the harness. We recommend these bundles be split up into inputs from sensors and outputs to injectors, coils etc. The coil cables in the white connector are best left outside any wire harness bundle. This keeps the higher current device signals from interfering with sensor inputs.


Inline connectors are often needed. Multiple connectors can be a source of trouble. We highly recommend running continuous wires from the ECU to all sensors, injectors, coils, etc. whenever possible. Every extra connection is a potential poor connection or disconnect. If a wire needs splicing, set the length, solder and heat shrink the connection.

Wiring Tip #4 - POWER SOURCE

We often see inadequate power supplied to the engine management system. Do not depend on the car's factory wiring to power an aftermarket engine management system. The factory wiring, especially on older cars may have weak connections and small wires that can cause voltage drops. Voltage drops with an engine management system cause hard starting, misfiring and a host of other irregularities. The power for the ECU, coils, injectors and fuel pump should come directly from the battery or battery cut-off switch to the power harness. The power harness has the relays and fuses needed for the system. Depending on the power requirements, this wire should be at least a 10ga wire, and 8ga for long distances coming directly from the battery or power cut-off switch.


The wiring and connections for an engine management system will determine the overall reliability of the system. Use wire that is specified for automotive applications and will stand up to engine compartment temperatures. Take the time to properly crimp, solder and wrap your wire harness. Use the correct tool to crimp the terminals. Use just enough solder for a sound connection. Do not let the solder wick outside the joint area, as this creates a stress riser and possible failure point over time.


The Electromotive power harness was changed in August 2004. The change was made so the ECU would receive true battery voltage. Before this change, the ECU would see the voltage supplied by the ignition switch, usually through the car wiring. This voltage would be often be .5 to 2 volts below battery voltage. If you have an older power harness, we recommend changing the connection of the yellow switched power wire in the gray ECU connector (pin G5). This wire should connect to terminal 87 on the DFU (coil) relay.


More Tips


Inconsistent sensor values

Inconsistent sensor values can be caused by poor terminal connections. We have seen instances where the terminals in the gray and white connectors have been spread open, causing a poor connection to the ECU. Carefully check each terminal with a .040 diameter pin. When the pin is carefully inserted into the terminal, there must be tension on the pin. If there is no tension, carefully remove the red terminal lock on the ECU connector. This procedure is in the TEC3r manual. With the terminal lock removed, all the terminals are in clear view. Each terminal has 3 fingers that make contact with the ECU connector terminals. With a pointed object, carefully push each of the 3 fingers to the center of all the terminals. Replace the red terminal lock, making certain that each terminal is fully seated in the connector. Verify that each terminal has tension on a .040 diameter pin. Don't neglect to visually check each sensor and injector terminals as well. We have seen a number of the sensor terminals which have been damaged, causing false readings.

Hard or slow starting

Hard or slow starting can be caused by a couple of conditions. Usually we find low battery voltage during cranking to be the cause. When battery voltage drops, fuel injectors respond more slowly. If the voltage drops low enough, the injectors will not deposit fuel. Check the voltage during cranking at the 87 terminal of the fuel pump relay. During cranking, 11 volts is the minimum desirable voltage. Below 10.5 volts the injectors may stop depositing fuel during cranking. At 9.5 volts there may be enough electrical noise in the power so that a crank signal may not be present. Any of these low voltage conditions will cause hard or slow starting.

If the battery voltages are good during cranking, hard or slow starting may be caused by programming. A cold engine will require extra fuel to start and run. A hot engine will take little additional fuel to start. In the WinTEC software under Enrichments, adjust the Starting Enrichments & Warm-up Enrichments values to improve your engine's starting characteristics. Remember, these values are cumulative. It is easy to get too much fuel and foul the spark plugs. For all starting enrichments, we suggest beginning lean and adding fuel until the desired amount of enrichment is achieved.

Rich mixture that won't lean out

We often receive calls from people whose engine always runs rich at idle, and when coasting down to idle. They can't lean out the mixture. This may be due to the minimum injector on time value being set too high. The minimum injector on time parameter is set for the amount of time the injectors need to deposit a measured amount of fuel. It is also used so that the engine won't go lean and stall when coasting to a stop. In the WinTEC software, this value is set under Wizard and Basic Engine Parameters. A good starting point is 1.1ms for low impedance injectors, and 1.5ms for high impedance injectors.

Stalling at idle or when cold

When an engine drops below its normal idle speed, the manifold pressure rises quickly. In this case engines whose fuel mixture is controlled by MAP will go rich. If not corrected, the engine will get richer as engine speed goes down, causing the engine to stall. To remedy this condition we program a column in our tables at approximately 300 RPM below our idle speed. Each cell in this column is set with the injector pulse at idle. This technique keeps the amount of fuel at idle correct for the engine idle speed, eliminating a stall due to an overly rich fuel mixture.

Blend, is it on or off?

When using the tuning Wizard, be aware that when you enter ‘Race/High Perf’ you are entering default values into the TPS/MAP Blend table. When using stock cams or improved grinds, start with the ‘Street/Stock’ setting. When tuning engines with high overlap cams, Blend is a great feature to achieve a stable idle. For turbo applications, the engine may have race cams and little overlap. For turbo cams start with Street/Stock and add values to the blend table only if needed.

Hard Starting in the morning?

If your engine is hard starting in the morning or when cold, look under Fuel Enrichments, Starting Enrichments the value for PWO. We often see this value at 0. This setting provides a fixed amount of fuel at cranking for the programmed time. Normally 4-6ms. It is also important to set CLT0 to a temperature about 15 degrees above your average morning starting temperature.

Spark Plug Wire Maintenance:

Due to the high voltage spark of the TEC, plug wires will break down over time. Even a wire that looks OK can be faulty. Looking for stray sparks on the wires in the dark with the engine running will catch most bad wires. Plug wires should be a normal maintenance item and replaced every year or two.

MAT Sensors:

A Manifold Air Temperature (MAT) sensor with its programmable fuel and ignition compensation parameters can improve an engine’s performance by adjusting to changing intake charge conditions, especially on turbo/supercharged engines, with or without intercoolers. A MAT sensor can give bad data if it is mounted in a hot manifold, so it should be isolated.

Fuel Pressure:

Fuel injector flow is rated at a constant fuel pressure across the injector. If the injector outlet is located below the throttle blade(s), the fuel pressure regulator needs to be referenced to manifold pressure to maintain constant pressure. That way, when manifold pressure goes up, fuel pressure goes up. When manifold pressure goes down, fuel pressure goes down. Fuel pressure across the injector remains constant.

Optimum Ignition Timing:

When searching for optimum ignition timing, first increase timing until maximum power is achieved. Then decrease the timing until power drops ever so slightly. This provides a detonation safety zone in case the fuel, air, or engine conditions change. If detonation is heard at any time, BACK OFF immediately.

Voltage Drop:

Voltage drops in the power and ground cables should be less than 0.5V when the engine is running. TO check, place the red lead of a voltmeter on the positive battery post. Then, with the black lead, check the switched battery connection at the TEC (SW BAT), the fuel injector +12V common supply, the + side of the fuel pump. If a large voltage drop is observed, the wire is too long, too small, or there is a bad connection.

Manifold Absolute Pressure:

Manifold Absolute pressure sensors should be no farther than 12" from the intake manifold plenum for good MAP signal response. Closer is better. Also, the MAP sensor hose should never be attached to a single runner of the intake manifold.

Tracking Calibration Files:

Use an increasing two-digit number at the end of your calibration filename to indicate progress. Change the number of your calibration file (making a new file) when making significant changes. You may want to go back to an earlier file if the changes do not work out. Use the comment section to indicate what types of changes were made from the previous file.

TEC Triggers and Timing:

When checking the ignition timing, never reference off of the TEC’s trigger wheel. The TEC will always time at the net advance according to the trigger wheel signal. Be sure to use an engine crankshaft timing mark.

Choosing the Correct Fuel Injector:

Increasing a system’s fuel pressure to increase fuel flow should be considered only as a last resort. There is a wide range of injector sizes readily available in the aftermarket to meet most any requirement. If you choose to increase fuel pressure, use the engine parameters part of the calibration software to find out just how high the fuel pressure could be with the increase you are considering. Do not go above 70 psi total pressure because it may cause erratic performance and/or damage the injectors.

Volumetric Efficiency Table:

Be careful adding fuel through the Volumetric Efficiency Table near the high RPM/MAP region. If the TOG and IOT values are set to fully utilize the maximum injector time, the injectors may not be allowed to fully recover (close) before they are turned on again. This will cause less fuel to be delivered than expected, possibly causing a lean mixture.