Mike Walsted's Thunderbird Turbocoupe Page
PC1 to LA3 Swap

The Thunderbird Turbo Coupe came with a variety of computers, depending upon transmission and vehicle year. The 1985 and 1986 Thunderbird Turbo Coupes with the 5 speed transmission came with 35 pound injectors, a small VAM, and a PC1 computer. The very last computer used in a 5 speed Turbo Coupe was the LA3, which used 35 pound injectors, a large VAM and came with a faster processor. The LA series also used an Air Charge Temperature Sensor, to better manage the fuel mixture.

Switching computers in the TC has made a noticeable improvement in the way the car runs. It accelerates better, idles smoother, and the RPMs climb more dependably. Even so, the amount of work involved does mean that it is not an undertaking to be taken as lightly as it might appear. Several decisions need to be made prior to undertaking the endeavor, and I wonder if it was worth the effort for the performance improvement, considering that this car is a daily driver and will not likely be used for racing.

Here is how I did the swap:

The first decision after committing to the installation involved installation of the ACT sensor. I installed mine near the bottom of the upper intake. This meant that the lower intake did not have to be removed. The upper intake did need to be drilled and tapped (with a 9/16th inch bit and 3/8th inch pipe thread tap), and that took a significant amount of time. The sensor is located between the runners for cylinders 3 and 4, not actually in the airflow, but occupying a space between the runners so that air can now go from the #3 runner to the #4 runner. Switching to the 1987/1988 lower intake would have negated the need to tap a place for the ACT sensor, but would have also eliminated the usefulness of the cooling fan switch, which activates the cooling fan in the earlier TCs.

After the ACT was installed, I installed the large VAM. I didn't pick up the turbo to VAM hose when I got it, so I had to find a substitute. I used a portion of the air-intake hose from a late 80s Bronco II to go from the turbo to the VAM. The rest of the VAM installation went without incident.

Next came the installation of the actual computer. I used this site and this wiring diagram as guides. Basically, I had to swap the wire from pins 43 to 27, 25 to 43, 32 to 31, and 35 to 33. I also added a wire to pin 25 for the Air Charge Temperature sensor, (using the wire on the sensor connector furthest from the corner on the connector,) and ran a wire from pin 24 to the Sig Return wire (pin 46). The wire on the ACT sensor connector nearest the corner on the connector was also wired to Sig Return.

Brake and Speed Sensor inputs also had to be installed. A wire was run from Pin 2 on the computer to the light green UNSTRIPED wire on the brake light switch at the brake pedal. Another wire was run from Pin 3 on the computer to the dark green/white wire on the speed control amplifier, and another wire was run from pin 6 to the black/white wire on the speed control amplifier. I haven't verified for sure that this is how the setup is supposed to be, but from what I can tell it should work.

Being incredibly paranoid, I retained the original fan controller, and also added relays so that if the old fan controller or either of the LA3 fan controllers would activate the fan, the fan is activated. The relays are available in the custom Fog Light section of some autoparts stores for around $4. I ordered and installed a PermaCool 16 inch fan from Summit Racing.

The WOT A/C cutout from the LA3 does not work the same as the one on the PC1. Consequently, the wire leading to position 3 on the cooling fan relay had to be removed to ensure that the air conditioning works. Prior to removing the wire, the A/C compressor would not run. Not a good situation in Texas.

All in all, I had to get the LA3, big vam, ACT sensor connector, and seven spare pins from the local salvage yard. I got a bunch of wire and connectors, three fog-light relays, and an ACT sensor from the local auto parts store. I got the 3/8 inch pipe tap from a good hardware store, and borrowed the 9/16 drill bit. The increase in available power (or is it torque?) meant that I had to buy a new motor mount insulator, Pioneer part number 602661, from Oreilly Auto Parts. Another car that I did the swap on also experienced noticeable performance improvements.

If you have any suggestions, please feel free to e-mail me at mike@mikewalsted.com.