Q: Do you have an advice for hooking up a new EFI kit?

Tips For Hooking Up Your ECU

Connecting the wires is an important step in getting your electronic fuel injection system or engine management system up and running. Following these guidelines will prevent headaches when installing and tuning your EFI.

Mounting the ECU

Some kits have the ECU built into the throttle body. If yours is separate, the best place to mount it is inside the passenger compartment. If you decide to mount it in the engine compartment:

  • Keep the ECU away from the exhaust, distributor, or places where it would have direct contact with water.
  • Mount it so the electrical connections point down to keep water out.

Power Requirements

The ECU needs stable voltage and sturdy connections.

  • Power should come directly from the battery terminal through a fuse.
    • This will save your tuning data when the key’s off.
  • Ground should also come directly from the battery terminal.
    • Make sure the engine ground is good as well.
  • You’ll need “keyed-on” power.
    • This should be its own circuit, not shared with the radio, lights, etc.
    • It also has to provide power while the engine is cranking.

Tach Signal

The tach signal can come from the tach output of your distributor (if equipped) or CD box. The negative post on the coil can also be used with non-CD type ignitions.

  • Connecting to the coil on a CD ignition will damage the ECU.


Most sensors are built into the EFI hardware. You may have to mount the O2 sensor and ECT sensor.

  • The O2 sensor should be no more than 8 inches after the exhaust collector, before the catalytic converter (if equipped), and at least 18 in. before the end of the tailpipe.
    • It should be mounted at least 10 degrees from the pipe’s horizontal center line so that moisture can’t collect inside the sensor.
Image/Summit Racing
  • Mount the ECT sensor in the head or intake manifold, not the thermostat housing.
    • Constant bypass flow will give false temperature readings.

Cooling Fan/Fuel Pump

The ECU can control the fuel pump and cooling fans. Hooking them up directly will damage the ECU. They should be isolated with relays.

  • Some manufacturers include these relays. It’s best to check the instructions.

A/C Fast Idle

If the ECU knows the compressor is kicking in, it can raise the idle. This signal, normally a ground, could come from the A/C clutch or A/C relay.

General Guidelines


  • Keep splices to a minimum.
  • Solidly crimp or solder splices.
  • Seal splices with heat shrink tubing.
  • Cap unused wires with heat shrink tubing.


  • Use solid core spark plug wires.
  • Run sensor wires near spark plug wires of any kind.

This is another in a series of weekly Q&A Mailbag sessions with Summit Racings tech department, in which there are hundreds more. Click here to see them all.