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ST205 Ignition System and Distributor

Fri Feb 08, 2019 4:38 am

Toyota in their workshop manuals and other workshop manuals or tech help give very little detail on the distributor
and the relationship to the ignition system. They just refer it as Toyota ECU Ignition System.

When you open up the ST205/3SGTE distributor, remove the distributor cap, rotor and rotor plate, under it and in
the bottom of the distributor you will see 3 Hall effect (magnet) sensors and a toothed wheel fixed to the distributor shaft.
Note here the distributor is driven off the exhaust cam.

Off the distributor are 4 wires which connect to the sensors. The sensors are :-
Crank Position Sensor NE
Camshaft Position Sensor G1
Primary Trigger Sensor G2

From what info. I can gather is:-
Crank position Sensor NE wire is a yellow wire and is connected to the Cranksync. In slot in the ECU
Camshaft position sensor G! wire is a Red wire and is connected to the Camsync. In slot in the ECU
Primary Trigger sensor G2 wire is a Blue wire and is connected to the Primary Trigger slot in the ECU.
The 4th wire a Black Wire is G- wire which I am not sure whether it is a positive wire or a negative wire
and connected to the ECU. It could be a ECU input connection or a output connection.

If you have already or are planning to install an aftermarket ECU it is important to know which of these wires
do what and where they connect to. If you are like me planning to use COP (individual coils) the distributor
becomes redundant in cylinder firing but the sensors and wires in the bottom of the distributor are crucial in
the operation of the ECU.

So can some one that has had some experience in this please help? I am not sure whether the above is correct
or not. Or whether the Black wire is negative or plus. My thoughts are that it is a positive wire (+5V supply wire)
and all other wires are ground inputs signals connections through the ECU. (like how your fuel injectors work)

The ECU I am planning on using has Camsync. In No1 and Camsync. In No2. but no Crank In, so I am going to
have to use one of the Camsync. In's for crankshaft position.

Please please can some one help here and give me some feed back. I believe some of the 2J's engines and the Caldina
have the same ignition and distributor set up.

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Re: ST205 Ignition System and Distributor

Fri Feb 08, 2019 9:25 pm

This is more specific to the st185 and megasquirt but the doc I have lists g- as a ground.

Re: ST205 Ignition System and Distributor

Sat Feb 09, 2019 12:47 am

Thanks for that Magroo

So what that Megasquirt chart is saying:- NE is the Primary Trigger sensor , G1 and G2 are both cam sensors and G- are sensor ground.

Recently talking to a guy that does setting up of aftermarket ECU's and tuning, told me that with the Celica GT4 ST205 you do not need additional
trigger wheels and sensors, as it all already exists with in the distributor, off hand he could not remember which wire/ sensor did what.
I am in the process of producing a wiring diagram of my harness modification and doing this for my own peace of mind.

I am sure this could be helpful to other member contemplating doing a ECU upgrade. Maybe all GT4's have this system.

Re: ST205 Ignition System and Distributor

Sat Feb 09, 2019 5:13 pm

I did almost exactly this when I went coil on plug. I mapped out the body and ECU harness when I was converting a 5sfe harness. It's for an st185 and megasquirt but it's similar.

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