The basics
| Spec | 3SGE / 3SGTE |
|---|---|
| Layout | Inline 4 cylinder |
| Displacement | 1998 cc (2.0 L) |
| Firing order | 1-3-4-2 |
| Cylinder 1 | The timing belt end (seen from the driver's seat) |
Enter the displacement, cylinder count and firing order in your engine setup first, and wire injector and coil outputs by cylinder number.
Which 3S do you have?
Toyota built five broad generations of both the naturally aspirated 3S-GE and the turbocharged 3S-GTE. The generation decides your trigger, ignition and load sensing, so identify it before you order parts.
3S-GE (non-turbo)
| Gen | Years | Ignition | Compression | What stands out |
|---|---|---|---|---|
| 1 | 1984-89 | Distributor | 9.2:1 | Has T-VIS |
| 2 | 1990-93 | Distributor | 10.0:1 | T-VIS dropped, ACIS intake introduced |
| 3 | 1994-99 | Distributor | 10.3:1 | Last distributor version |
| 4 (red or grey top) | 1997 | Direct fire | 11.1:1 | BEAMS with variable intake cam only, cable throttle |
| 5 (black top) | 1998 | Direct fire | 11.5:1 | BEAMS variable timing on both cams, electronic (ETCS-i) throttle, returnless fuel |
BEAMS is Toyota's acronym for Breakthrough Engine with Advanced Mechanism System.
3S-GTE (turbo)
| Gen | Years | Ignition | Compression | Injectors | What stands out |
|---|---|---|---|---|---|
| 1 | 1986-89 | Distributor | 8.5:1 | 430 cc top feed | T-VIS, MAF load sensing, single-entry turbo, water-to-air intercooler, no blow-off valve, about 9 psi |
| 2 | 1990-93 | Distributor | 8.8:1 | 430 cc side feed | T-VIS and MAF, twin-entry turbo with two wastegate ports, air-to-air intercooler, BOV on MR2s, about 11 psi |
| 3 | 1994-99 | Distributor | 8.5:1 | 540 cc top feed | No T-VIS or MAF (MAP based), CT20B turbo, BOV fitted, about 13 psi |
| 4 | 1997-2001 | Direct fire | 9.0:1 | 550 cc top feed | CT15B turbo cast into the manifold, side-feed intake, nitrided crank |
| 5 | 2002-07 | Direct fire | 9.0:1 | 550 cc extended top feed | Center-feed intake, oil filler on the exhaust cam cover, no oil cooler, OBD2 from the factory |
Trigger systems
Distributor engines
Every distributor 3SG shares one setup inside the distributor: a 24-tooth reluctor pickup for trigger and two single-tooth pickups for sync. All the reluctor negatives share one ground return that Toyota labels G-.
| Toyota signal | OEM wire color | What it is | Connect to Haltech |
|---|---|---|---|
| NE | Black | 24 tooth | Trigger + |
| G1 | Green | Single tooth | Home + |
| G2 | White | Single tooth, 360 degrees from G1 | Leave unconnected |
| G- | Red | Shared return | Signal ground |
Crank-triggered engines
Later engines move the trigger to a 36-2 wheel on the crank read by a reluctor sensor. What changes is the cam side:
- Without BEAMS: one reluctor pickup on the cam reading a single tooth.
- With BEAMS: each cam carries a 3-tooth reluctor target.
On these engines the sensor negatives are joined into one wire, which Toyota calls NE-.
| Factory signal | Haltech connection |
|---|---|
| NE+ (crank) | Trigger +, the yellow wire in the trigger 4-core |
| G2+ (intake cam) | Home +, the yellow wire in the home 4-core |
| GEX (exhaust cam) | Any free SPI |
| NE- | Signal ground, the blue wire in the trigger 4-core |
Like the 4AG and similar Toyota reluctor setups, 3SG signals often sit biased below 0 V, commonly crossing around -0.25 V instead of at zero. A default reluctor setup can miss or mis-count teeth as a result, so these engines usually need a custom trigger configuration. Haltech publishes screenshots of working trigger settings for the distributor, Gen 4-5 3SGTE and BEAMS engines. Ask us and we'll send the right one for your version along with advice for your build.
If reluctor triggers are new to you, our trigger systems explainer covers the theory.
Ignition
Distributor engines: external igniter
The igniter's pin labels are printed on the underside of its connector. You only need one wire from the Haltech: ignition output 1 to the IGT terminal (white). Coil negative (C), tach (EXT), coil positive (B) and the IGF feedback line don't connect to the ECU.
Direct fire engines
All direct fire 3SGs use coils with the igniter built in, so each coil takes its own ignition output directly. Dwell times differ between the distributor igniter and the direct fire coils. Haltech lists a dwell table for each, which we can send on request.
Sensors
Throttle position (MR2)
| Pin | OEM color | Job |
|---|---|---|
| 1 | Brown | Signal ground |
| 2 | Purple | Idle switch (not needed) |
| 3 | White | TPS signal |
| 4 | Red/Blue | 5 V supply |
MAP sensor
From Gen 3 the 3SGTE runs a factory MAP sensor, but it tops out around 126 kPa, which a modified turbo engine passes quickly. We normally use the Haltech ECU's internal MAP sensor instead, or fit a higher-range external one such as the 3 bar GM MAP sensor. For reference, the Gen 4 factory sensor pins are E2 (pin 1, brown) signal ground, PIM (pin 2, yellow) signal, and VC (pin 3, light green/red) 5 V.
MAF sensor (early engines)
Gen 1 and 2 turbo engines measured airflow with a MAF. A Haltech can read it, but almost everyone converts to MAP-based load, which is exactly what Toyota did from Gen 3. If you keep the housing, pin 4 (VC, red/blue) is 5 V, pin 5 (E2, brown) is signal ground, pin 6 (VS, yellow/blue) is the airflow signal to an AVI and pin 7 (THA1, black) is the built-in air temp signal to another AVI. Pins 1-3 aren't used.
Coolant temperature
It lives near the top radiator hose outlet. Polarity doesn't matter. Use the Temperature - Toyota 1FZ-FE Coolant Sensor.cal calibration, which assumes the ECU's 1k pullup to 5 V is on.
Intake air temperature
MAF engines read air temp inside the MAF, and MAP engines have a sensor in the airbox. Neither spot suits a boosted engine because neither sees the charge after the intercooler. Replace it with a screw-in sensor like the Haltech air temp sensor and mount it after the intercooler, ideally in the plenum close to the MAP sensor take-off. The factory air temp sensor isn't polarity sensitive and its calibration also assumes the 1k pullup.
Idle control valve
The 3SG uses a two-coil rotary idle valve that rests half open. One coil drives it further open, the other drives it closed. It needs two ECU outputs and switched 12 V. In the software, set it up as a 3-wire BAC valve with the type set to Bi-Directional.
| Pin | Job | Haltech connection |
|---|---|---|
| 1 | Open coil | Spare output |
| 2 | Supply | Switched 12 V |
| 3 | Close coil | Spare output |
Some cars also have a simple on/off air valve that opens with the A/C. Drive it from a generic output that switches on whenever the A/C output is active.
Finding the factory ECU
On the MR2 the factory ECU sits in the trunk, on the firewall. Celica locations vary by model, and Haltech has photos of both. Ask us if you need them.
3SG FAQ
Can I keep the distributor?
Yes. Wire it as described and the Haltech controls timing through the factory igniter. Many builders later convert to coil-on-plug, but it isn't required to get running.
Why does my 3SG lose sync at higher RPM?
On these engines the usual suspect is the negative-biased reluctor signal. Check the trigger settings against a known-good configuration and capture the signal with a scope if needed.
Working on another Toyota? See the 1JZ/2JZ and 1UZ-FE guides, or book a free consultation with us.
