This page will go over the basic fundementals of buying and installing a Holley EFI system on an LS series engine. 

Here is a link to the Holley Dominator ECU and harnesses to get started.

Holley's site is just "ok". For whatever reason Holley does not have all the EFI components in one spot. You will have to browse around between EFI components, LS stuff, etc.

For a very basic turbo LS car that doesn't need a lot of inputs and outputs, controlling components or an electric control trans, the Holley HP version of the EFI system can be used to save around $800. I use this on my personal car. The HP has 4 inputs and 4 outputs. For example, boost control would use one input for the dome pressure sensor and two outputs to the increase and decrease solenoids. Fan(s) is one output, second fuel pump is one output, two step rev limiter is one input. Pretty much full...

If you need to power a 60E or 80E trans and are the type that want to monitor everything, the Dominator is the better choice. Additional inputs are now easily added. Monitor everything you desire, oil temp, backpressure, etc., etc. 40 inputs and 40 outputs!

The usual turbo LS car will need:

Dominator ECU

Main power harness

LS1 or LS2 engine harness

Injector harness (couple options)

Transmission harness

Input/output harness

(2) boost solenoids

3 or 5 bar map sensor

(3) 100psi pressure sensors. Oil, fuel, and dome pressure.

Overview: I will be documenting the steps I use to install the pre-terminated LS harness into the car while incorporating a transmission harness and boost controls into a complete harness.


1. Basic layout:

Take the engine harness out of the box and lay it out in the engine bay. Take note where the fuel injector pigtail is. That needs to be at the center rear of the engine. From that point you have about 48" of harness length to mount the ecu somewhere behind the firewall or at least away from heat sources.


2. Mounting ecu:

Mount ecu in the chosen location using the provided bolts from Holley. This particular car (83 Cadillac) has a nice space where the glovebox was.


3. Loose leads:

The Holley LS harness has several loose leads. Some come out near where the harness passes through the firewall and some are closer to the ecu connectors. I prefer to remove all the wiring loom and tape and reroute all the loose wires and input/output connector back towards the ecu connector.

The picture below shows the loose wires that can stay where they are.

 The picture below shows the loose wires that are up by the pass through to the engine compartment. These are the ones I prefer to pull back near the ecu.


4. Ignition:

I usually remount the ignition coils down low on the block, therefore, I pull the loom and tape off that part of the harness and move the ignition harnesses down with the sides of the block. Plenty of length there already.


5. Map:

The 3 bar map typically used is not plug and play with the LS harness. The pigtail is provided so just cut it to the proper length for wherever you are mounting the map and crimp on the supplied terminals. I use Mack Tools crimper part #.


6.   Boost:

The proper setup for boost control will have two solenoids. One increase solenoid and one decrease. These will be mounted somewhere out of the heat effected zone but as close to the wastegates as possible. Also install a 100psi Holley pressure sensor into the top of the wastegate(s) for use as a dome pressure sensor. Each solenoid has two wires. One goes to key on 12v and the other will be receiving signal from the ecu and gets routed to the input/output harness on the main harness. It can also be routed to the ecu to a separate input/output connector if you choose. The dome pressure sensor needs one signal wire to the input/output connector, one to a 5v signal (you can snag a 5v signal from one of the four orange wires leading from the ecu connector), and one to ground.


7. Transmission:

Route the transmission harness from the trans connector up to the rear of the engine and combine it into the main harness.


8. Add ons:

Even if you are not using any additional sensors for monitoring it is a good idea to install a few extra wires into the harness now to make it easy later. Oil temp, turbo backpressure, etc. A lot easier later on if all you have to do is terminate the ends. A couple other wires that need installation at this point are a relay activation wire from the input/output harness out through the harness to the electric fan(s).

 9. Rewrap the harness with tape and loom. You should now have a harness ready to go. The grommet needed to pass though the firewall is approx. 1 1/2"ID and 2" OD. I usually buy things like this from McMaster Carr. The king of hardware you need when building a car.


10. Pinmapping and terminating wires:

I don't think I can improve upon Holley's instructions on how to do this so I won't rewrite it. The instructions are good.


11. Dash:

There are several options for a dash display. Holley has the LCD screen. You can also use a Windows compatible tablet. The last option would be to not use anything and just connect a laptop when tuning and monitor the car with other gauges.

I will be revising this as needed, adding some more details, and more pictures so check back soon.

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