Monday 30 April 2018

TOYOCOM:: Universal mode with a carburetor.


A year ago I was given a 1990 tercel DX coupe. It had issues to fix and I was glad to know how to.
It was then 28 years old while still showing under 100k km (about 60k miles) on the clock.

It got fixed here and there in the last year span; tires,suspension,brakes,body panels and exhaust system, engine valve seals and timing belt to name a few. The good old trusty 3E grew on me in that time lapse since it was so reliable, overshadowing the fact it is under powered to the extreme.


It has got 82 hp and an A/T 3 gear transmission. starts like a charm on cold weather

It's an 1.5L 3E engine from 86 to 90. This engine uses a carburetor and a computer to control some peripherals and monitor it's overall operation. Very few existing sensors are useful on it, an oxygen sensor is there at least. all other sensors are switches. no analog sensors at all.(digital throttle position switch and digital temperature and vacuum switches)
The vacuum diagram is as complicated as a wiring diagram for a much more complex was the time where carburetors had to let got to full EFI.

Only E1(ground) and the VF (fuel trim) were available in the diagnosis box for the TOYOCOM to use. not even switched power (+B). Improvements had to be made to take full advantage of this setup.


An android car radio was installed to be able to gather data all the time from the TOYOCOM unit installed in the engine bay (blue box in the upper right corner of the preceding picture). this radio is setup to connect to the TOYOCOM every time TOYOBD1 starts.
  • VF is already there
  • E1 is already there
  • +B was routed from the engine harness reaching the fuse box.
  • Ox(oxygen sensor)  was routed into AB
  • Moving speed is taken from the android car radio GPS
Even though there were still custom inputs available on the TOYOCOM nothing else was routed to the diagnosis box yet.


  • the alternator is poorly working but still operational. (battery voltage is low under all conditions)
  • the engine runs rich while idling and lean when held at WOT for a long time in 2nd or 3rd gear. it might have fuel delivery or carburetor issues
  • the fuel trim is always negative ,meaning the ECU suspects the fuel consumption is less than expected. It might be the oxygen sensor, might be fueling issues again
  • throttle position and temperature switches are working OK, the system goes from closed to open loop following engine load and growing engine temperature.


More custom sensors are to be mounted on the engine to even out MPG calculations reserved only at this time to EFI engines. more sensors will be added to monitor the engine tune and improve it along the way as possible.
  • fuel flow sensors on fuel lines
  • MPG calculations for a carbureted engine in TOYOBD1
  • dirt cheap wideband oxygen sensor setup
  • rpm input from the igniter