4AG at a glance
Every 4AG is a 1.6-liter Toyota twin-cam four. The basics that matter for ECU setup are the same across the family:
| Item | Value |
|---|---|
| Cylinders | 4, inline |
| Displacement | 1587cc |
| Firing order | 1-3-4-2 |
| Cylinder 1 | The end nearest the timing belt (viewed from the driver's seat) |
Which 4AG do you have?
The variant decides your load sensing, injection strategy and trigger. Here's how they line up:
| Engine | Load sensing | Fuel and spark | Notes |
|---|---|---|---|
| 4AGE big port, 1st gen ("blue top") | Vane MAF on US cars, MAP on JDM | Batch fire, distributor, 182cc injectors | 16 valve, T-VIS switching around 4200 rpm, 9.4:1 |
| 4AGE big port, 2nd gen ("red/black top") | MAP on all versions | As the 1st gen | Same basic engine, all speed-density |
| 4AGE small port, 3rd gen ("red top") | MAF on US cars | 235cc injectors | No T-VIS, 10.3:1, stronger bottom end |
| 4AG 20V "silver top" | Vane MAF | Sequential, distributor, 295cc injectors | Five valves per cylinder (three intake), switched intake cam timing, individual throttle bodies, 10.5:1 |
| 4AG 20V "black top" | MAP | Sequential | As the silver top with 11.0:1 compression |
| 4AGZE big port | MAF | Batch fire, wasted spark, 365cc injectors | Factory supercharger with an ECU-controlled clutch |
| 4AGZE small port | MAP | As the big port |
With a Haltech you'll normally run speed-density on a MAP sensor regardless of what the factory used, so a MAF engine isn't a problem. Just plan for a MAP sensor and a vacuum source.
Distributor and trigger
Every 4AG trigger we've seen uses reluctor (magnetic) pickups inside the distributor, but the tooth counts vary:
| Pattern | Found on | Haltech setup |
|---|---|---|
| 24 teeth plus 4 teeth | Some big port 4AGE | Needs modifying: remove three of the four teeth so it becomes 24 plus 1 |
| 4 teeth plus 1 tooth | Some 4AGE | Generic, Standard Full Cycle Sync |
| 24 teeth plus 1 tooth | Other 4AG distributors | Toyota 4AG trigger type |
| 24 teeth plus 1 tooth (cam sensor) | 4AGZE | Toyota 4AG trigger type |
You may hear of a distributor with only four teeth on the lower wheel. That one most likely came off a 4A rather than a 4AG.
Distributor wiring by engine
On the big port 4AGE (after the 24 plus 1 modification) each pickup has its own pair of wires. For both pairs, red is positive and white is negative:
- 24-tooth (NE) pair: red to Trigger +, white to Trigger -.
- 1-tooth (G) pair: red to Home +, white to Home -.
The 4AG 20V and 4AGZE share one ground between the pickups and have a second 1-tooth output (G2, offset 360 degrees) that you leave unconnected:
| Signal | 4AG 20V | 4AGZE | Connect to |
|---|---|---|---|
| NE (24x) | Pin D, black | Red | Trigger + |
| G1 (1x) | Pin C, red | Green | Home + |
| G2 (1x, 360 degrees later) | Pin B, green | Yellow | Leave unconnected |
| G- (common ground) | Pin A, white | White | Signal ground |
A known 4AG trigger quirk
4AG reluctor signals often don't sit centered on 0V. They tend to lean negative, commonly crossing around -0.25V, which can upset default trigger thresholds. It's common to need a custom trigger configuration to get a clean, stable signal. If you're chasing trigger errors on a 4AG, ask us for the settings we start from, and read up on arming voltage in the meantime.
Shortcut for single-cable trigger wiring on Elite harnesses
On a CAS or distributor with a dual Hall effect pickup, the Trigger - wire in the Elite harness's shielded trigger cable is spare. You can repin it at the ECU plug so it carries Home + instead, putting power, ground, Trigger + and Home + all in one cable. After this change, the green wire labeled Trigger - is really Home +.
- Elite 550 / 750 / 950: on the main connector, pull the yellow Home + wire from pin 32 and insulate it. Move the green Trigger - wire from pin 33 into pin 32.
- Elite 1000 / 1500 / 2000 / 2500: on the 26-pin connector, pull the yellow Home + wire from pin 2. Move the green Trigger - wire from pin 5 into pin 2.
In both cases, unlock the connector with its large white tab first (the two smaller tabs pop up), seat the moved pin fully so it sits level with its neighbors, then press the tabs back down until they click.
Ignition
Whatever the model, ground the igniter's body to the chassis. Only the ECU signal wire (IGT, plus IGD on the 4AGZE) goes to the Haltech. The fail signal, tacho and coil negative aren't connected to the Haltech.
- 16 valve distributor engines use an oil-filled canister coil with the igniter bolted alongside. On the AE82 the IGT wire is black/blue. On the AE92 it's pin 2. Either one goes to Ignition Output 1 (yellow/black).
- 20 valve distributor engines use a higher output coil with a separate igniter. The ECU signal is pin D, to Ignition Output 1.
- 4AGZE runs wasted spark from a combined igniter. On its 6-pin plug, pink (IGT) goes to Ignition Output 1 (yellow/black) and white (IGD) goes to Ignition Output 2 (yellow/red). The 2-pin plug carries coil negatives for cylinders 1 and 4 (light blue) and 2 and 3 (black).
The igniter's 12V feed is still needed. Keep it on a switched supply.
Sensors and actuators
| Part | Hookup | Notes |
|---|---|---|
| Throttle position sensor | Pin 1: 5V, pin 2: signal, pin 4: signal ground | Pin 3 is the idle switch. You don't need it with a Haltech |
| MAP sensor (AE92) | Brown: signal ground, yellow: signal, light green/red: 5V | Or fit a Haltech MAP sensor |
| Idle valve (20V) | Pin 1: open signal, pin 2: switched 12V, pin 3: close signal | Two spare outputs; set up as a 3-wire BAC valve |
| Coolant temperature | Two wires, either way round | At the back of the head above the bellhousing. The Toyota 1FZ-FE coolant calibration suits it |
| Air temperature | Two wires, either way round | Needs a pull-up on the Haltech input |
The 20V idle valve is the odd one out: it's a dual-solenoid unit, with one output driving it open and another driving it closed. See idle control for tuning once it's wired.
Our 4AG checklist
- Identify the engine and the distributor tooth pattern before you order anything.
- Choose the trigger type from the table above and check the signal with a trigger scope.
- Confirm timing with a light before tuning, see calibrating ignition timing.
- Ground the igniter body and connect only the igniter's ECU signal wire(s) to the Haltech.
Other Toyota engines are covered in our 1JZ/2JZ and 1UZ-FE guides.
4AG FAQ
Can I run a 4AG sequentially on a Haltech?
With a distributor that gives a 24-tooth and a single cam tooth signal, the ECU has full engine cycle position, so sequential injection is possible even on engines that were batch fired from the factory.
My 4AG throws trigger errors at idle. What should I check first?
Scope the signal. The negative offset described above is the common cause, followed by a worn distributor shaft or poor shielding on the trigger cable.
