TR3A EFI Update

Last update explained the upgrade to MS2 Extra that allowed me to fit wasted spark ignition and semi sequential fuel injection. That all worked well but I was not finished yet.

The next logical (if there is any logic to fitting EFI to a TR3A) step was to go MS3 with the MS3X expansion board. Sound’s grand but it only involves the fitting of a new chip and an expansion board that allows a number of new options. It still uses the original MS2 mother board but is fitted to a larger case to encase the extra expansion board.

There were no mods required to the engine but it did require some wiring changes, and fitting a few new items. As I had made changes to the EFI loom over the years, yes its been years, I elected to make a complete new loom. The new case fitted in the original position under the battery box.

The new features to be incorporated included, VSS (vehicle speed sensor), oil pressure logging, fully sequential injection, low oil pressure/high coolant temperature warning light, shift light, and emergency coolant pump switch ( remember I use an electric water pump, controlled by its own ECU, in lieu of the mechanical unit).

There are numerous other features available but not of any real benefit to the old TR like boost control, CAN (the ability of the engine to communicate with other vehicle systems, eg auto box), coil on plug, water injection, duel fuel, launch control (must admit I thought about that one), flat shift, knock control, etc. Knock control is still on the agenda but given the mechanical noises produced by the TR I am not sure it will work well enough to make it worthwhile.

Fitting the oil pressure sensor was easy with a line taken from the main oil gallery to provide the pressure. The VSS sensor was not so easy. Where do you get a signal that is speed dependant. I elected to use the gear box output flange. I fabricated four steel U pieces that bolted to the four tail shaft retaining bolts to provide four steel fingers that would trigger a hall effect sensor. This sensor was fitted to a fabricated mount bolted to the rear of the overdrive. I balanced the four fingers to ensure the tail shaft was still balanced. The wiring for this sensor was then included into the loom that takes the overdrive control wiring to the gear box.

Now I have a VSS, I can look at fitting a cruise control????

To house the new warning lights, I fabricated a small panel that fits under the top dash dress trim between the tacho and speedo. In this panel, I fitted the following. 1. Momentary push button switch to start data logging to a SD card. 2. Blinking red LED for low oil pressure/ high coolant temp. 3. A white LED to indicate that the data logging is in progress. 4. Two orange LEDs to indicate the first stage of shift control. 5. Two red LEDs as the final stage of shift control. Fitting a separate panel negated the need to modify the original dash and put the lights in the best position to see them. The shift lights are set at 5600RPM for stage one and 5700RPm for stage two. The rev limiter is set at 5800RPM. On the track, I try and shift between 56 and 5700RPM.

To enable fully sequential injection I needed to be able to tell the ECU when to fire the injectors relative to the stage of the cycle for any particular cylinder. This also applies to COP (coil on plug) if fitted. The ECU already knew the crank position because I had fitted a toothed trigger wheel on the front pulley as part of the MS2 Extra upgrade but it did not know if the piston was coming up on compression or exhaust on number one cylinder. It did not matter with wasted spark as both one and four were fired simultaneously. Hence wasted spark.

To achieve this I needed to fit a sensor that travelled at half engine speed, a cam sensor. This is inbuilt into modern engine cylinder heads. On the TR it was easier to utilise the distributor drive to give a cam sensor signal. I modified an old distributor body to house a hall effect sensor. The top of the distributor housing was cut off just below the vacuum fitting. The drive was cut off where the advance mechanism plate was attached. A single steel leaf was attached to the top of the drive so that it moved through the hall sensor that is screwed to the bottom of the distributor housing. A flat aluminium cover was made to cover the open housing.

Now what happens, is that the ECU is receiving a constant update on the cranks position from the crank trigger wheel. The cam position sensor sends a signal to tell the ECU that the next TDC is for number one cylinder, compression stroke. All other crank positions are calculated by the ECU from this information and updated every cycle.

This is about the end of the saga but like any good serial, I have left open the possibility of another episode…..the knock sensor.