Wiring A Factory ECU Into Your LS-Swapped Muscle Car Can Truly Be Painless

There are hundreds of magazine stories that mention about how easy it is to swap an LS engine into an early Chevelle, Camaro, or other GM vehicle of your choice. But that doesn’t mean this conversion just falls into place. The mechanical part has been covered in detail, but there are literally dozens of other… The post Wiring A Factory ECU Into Your LS-Swapped Muscle Car Can Truly Be Painless appeared first on The Online Automotive Marketplace.

JayLeno

Dec 10, 2024 - 07:50

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Wiring A Factory ECU Into Your LS-Swapped Muscle Car Can Truly Be Painless

There are hundreds of magazine stories that mention about how easy it is to swap an LS engine into an early Chevelle, Camaro, or other GM vehicle of your choice. But that doesn’t mean this conversion just falls into place. The mechanical part has been covered in detail, but there are literally dozens of other decisions necessary along the way. We’re going to take just one portion of that swap and dive into the details of adapting factory ECU control for a generic Gen III LS engine and trans into a Chevelle.

The LS-Swapped Chevelle That Will Receive The Painless Upgrade

This is the overall harness we used for the Chevelle’s conversion to a factory 411 EU. We ordered a harness with extra length in order to position the ECU inside the Chevelle interior. This particular harness was also for a mechanical throttle body but Painless also offers harnesses for drive-by-wire throttle bodies.

In our particular case, we started with Eric Rosendahl’s really nice ’67 300. The author upgraded a 2001 Gen III 5.3L truck iron block engine with bigger pistons to punch it out to 5.7 liters of displacement and complemented the build with a conservative Comp hydraulic roller cam and an LS2 Camaro mechanical throttle body intake. The Chevelle had been previously powered by a stout 383-cu.in. small-block with a Tremec five-speed, but Eric preferred a more docile 4L60E automatic trans.

Once the cable throttle pedal and shifter conversions were completed, it came time to locate an ECU and the appropriate wiring harness. Painless Performance offers several factory “411” ECUs in which the company has removed the GM PassKey anti-theft applications to make the ECU functional, along with a complete wiring harness.

To start, Eric laid out the wiring harness in the car and split it to direct the wires to their respective locations.

The Painless ECU we selected was loaded with a stock 5.7L LS1 Camaro tune, along with all the controls for a 4L60E automatic transmission. We then chose the appropriate engine harness with extra-length wiring that we figured could be useful for locating the ECU somewhere within the interior.

The next step was to lay out the harness and ECU to determine a suitable location. This also demanded that we position the harness to allow easy access to the bank of eight fuses and two relays that control power to the various systems. The Chevelle had bucket seats without a console, but Eric determined he could mount the ECU under the front passenger seat and position the fuse box inside a center console, while still offering plenty of room to route the wires under the hood. Best of all, the entire system was hidden from view.

We finalized placing the ECU under the passenger front seat and found that if we routed the large harness through and underneath the console that it could be completely hidden from view. We did have to space the passenger seat up roughly 1/4-inch to clear contact with the ECU with the heaviest guy we could find sitting in the passenger seat.

We won’t go into every detail due to space considerations, but there are a few items that are worth mentioning. At all times we read and followed the detailed Painless instruction sheet. For the most part, the harness is supplied with the connectors in place. However, in situations where wires needed to be extended or custom-terminated, we used simple non-insulated crimp connectors followed with shrink wrap insulation. This process takes slightly longer to complete, but is more professional and certainly looks better. Under no circumstances should you use those cheesy blue Scotch Lock crimp connectors for any electrical connection on any car – period.

Routing The Painless Wiring And Other Ancillary Tasks

This 8-fuse box with relays is located on the wiring harness very close to the ECU. Eric determined there was just enough room to position these fuses and relays inside the console box by cutting an access hole in the bottom of the console floor. This placed the fuses where they could be easily accessed yet still hidden from view with the console lid closed.

Once the ECU was located, Eric picked up a reproduction center console and cut a hole in the center storage area to fit the fuse block and relays. The rest of the harness was then routed underneath the console and we cut a 1 5/8-inch hole in the firewall, centering the hole so that it would be low enough to be unobtrusive with the engine in the car. We insulated the new harness port on the firewall with a Seals-It two-piece seal.

All of the connections for the Painless harness are clearly marked, so making the connections was rather straightforward. That included plumbing the air inlet and the mass airflow sensor. Controlling the alternator can sometimes be confusing, but a simple four-wire connector on the alternator with the “L” terminal directed to the charge indicator lamp in the dash will solve the problem. If the idiot light is not used, Painless offers a connector with the proper resistor wired in to accommodate this connection. This connection is used as a voltage sensing wire for the internal voltage regulator.

Routing the thick harness through the firewall, we located a suitable location that was roughly in the middle of the engine using a Seals-It firewall grommet to protect the harness where it passes through the firewall.

This Painless ECU harness can also accommodate all the emission control devices such as the EGR, vapor canister purge, air pump operation, and others. These are all positioned in a separate wiring loop that we coiled out of sight and not used as our application did not require these components.

Eric did want a separate aftermarket tach and the Painless harness includes a white wire for the tach. However, this white wire is intended for use only with a late model factory rev counter and not for use with the more common aftermarket tachometers. There is a budget work-around using a resistor for the power-up circuit but Eric decided instead to employ a simple Dakota Digital electronic box that converts the factory ECU signal to one compatible with an aftermarket tachometer.

We also installed a freshly rebuilt 4L60E automatic and connected the transmission to the ECU harness. We retained the factory-calibrated shift points.

This Dakota conversion box could also be employed to drive an electronic speedometer like the slick speedo unit sold by Dakota Digital. This way the conversion box takes output speed signal from the vehicle speed sensor (VSS) which can then be easily manipulated to send an accurate speed signal to the electronic speedometer. This eliminates that annoying speedometer needle wobble that is so common with older cable-driven speedometers from the ‘60s.

The Painless harness also came configured with outputs to control a pair of aftermarket electric fans. The harness connections are present as ground-triggers to be signaled by the ECU. This required a pair of 40-amp relays that were purchased separately. Eric found a handy relay box with six 40-amp relays that allowed him to not only trigger the electric fans, but to also increase the voltage to his headlights to make them significantly brighter.

The 4L60E requires a brake pedal signal to disengage the torque converter clutch when the brakes are applied. This requires a four-pin brake light switch that accommodates the brake lights while also signaling the transmission to disable the torque converter clutch. We’ve listed one of the Painless four-pin brake light switches in the Parts List below.

The single brown wire in the harness is for the exciter or “L” connection on a modern LS alternator. Painless offers the proper harness plug and we connected it to the charging system warning light on the dash. If the warning light is not used, Painless offers an 85-watt resistor that must be included in the circuit. If straight 12-volts is applied to this connection, the alternator will quickly fail.

Eric wanted to retain the original Chevelle cable-driven speedometer, but the 4L60E is not equipped with a mechanical cable drive. The solution was a SpeedHut drive box that uses the 4L60E’s vehicle speed sensor (VSS) electronic output as the signal to spin the speedometer cable with an electric motor. It took little time to dial in the speedometer’s accuracy, but it was not difficult.

Testing The New Painless Wiring And Factory ECU

Once the Painless harness was completely connected, Eric and crew test fired the engine for the first time to see if the package would actually work as advertised. Painless describes in the instruction that the first attempt at starting and idle demands that the engine will need to achieve a coolant temp of at least 176 degrees F and then idle in gear (with an automatic) for five minutes.

We discovered that we had to run through this several times, since we had not completed the entire installation after the first engine start test. This meant we had to disconnect battery power several times before the entire build was completed. This required the ECU to shuffle through this idle learn procedure each time. But each time the engine quickly achieved a solid, smooth idle.

Eric found this OBD Link+ connector online through Amazon that plugs into the Painless OBDII connector that then sends data to your smart phone via Bluetooth that can be fun, if for nothing else than impressing your friends.

Among the information that the OBD Link+ will send is displayed on a smart phone is vehicle speed, engine temperature, engine rpm, charging system voltage, and fuel rate in gallons per hour.

Eric also added a cool little device that he found online called an OBD Link+ that plugs into the Painless OBD-II port and wirelessly links the ECU to your smart phone. Eric set this up and used a separate software package to configure his smart phone with a custom dash, displaying any number of different items like vehicle speed, engine rpm, engine coolant temperature, system voltage, and even fuel usage displayed in gallons per hour.

Once the system was up and running we took the Chevelle to Westech Performance where Eric Rhee spent about an hour or so tuning the final package. The part throttle fuel was right on the money and only required a slight tweak of the wide open throttle fuel. As a near-stock 5.7L LS with factory cathedral port heads and a small 219 at 0.050 camshaft, the LS still managed 325 rear-wheel horsepower, which indicated that the engine was making right around 425 flywheel horsepower.

Eric has now logged several thousand miles on the conversion with no significant issues. The entire drivetrain package is very close to factory and promises to easily deliver fun-filled cruising for perhaps another 100,000 miles. There’s something to be said for late model performance and reliability.