Applications GM LT1
Draft. Trigger offset has not been confirmed on a running Race Core install. Pins marked TBD are unknown — do not guess them. A wrong decoder or firing order can destroy the engine.
GM LT1 (Gen II)
1992–1997 5.7 L small-block, 5733 cc, Optispark distributor under the water pump. Firing order is the classic Chevrolet order 1-8-4-3-6-5-7-2. It is not the LS order 1-8-7-2-6-5-4-3 on the LS1 note, and the Optispark is not a 24x crank. There is no Optispark mode in the rusEFI trigger list this note was checked against.
Recommended: Race Core F7. Eight high-Z injectors. One ignition output into an igniter while the Optispark cap is still distributing spark, or eight logic coils after a crank-trigger conversion. Do not load the LS1 24x decoder onto an Optispark.
Status: draft. Trigger offset has not been confirmed on a running Race Core install.
- Cylinders: 8
- Displacement: 5733 cc
- Firing order: 1-8-4-3-6-5-7-2
- Orientation: Cylinder 1 is the front cylinder on the left bank (US driver side). Odd cylinders on that bank, even on the other, front to back. Firing order 1-8-4-3-6-5-7-2. An LS firing order on this crank is an engine failure.
Variants
| Variant | Years | Trigger | Notes |
|---|---|---|---|
| LT1 Optispark | 1992–1997 | Optical distributor — no named mode | Cap and rotor, one coil, batch or sequential fuel depending on the PCM year. High-Z injectors. |
| LT1 with 36-1 or 24x | Conversion | 36-1 + cam, or a real 24x wheel | Use 24x only after the reluctor is a 24x. Then the LS1 decoder section applies to the wheel, and this firing order still applies to the crank. |
Recommended pin assignment (Race Core F7)
Pins below are the library default Race Core F7 map — the same AMPSEAL landings as the verified 1UZ-FE, 2JZ-GTE and LS1 notes. Core EFI V4 and Micro Core cavity numbers are TBD. If a pin is not in this table, it is TBD. Do not guess a spare.
| Pin | TunerStudio | Function |
|---|---|---|
| B10 | Digital 1 | Crank Hall |
| B1 | Digital 2 | Cam Hall |
| A3 | Lowside 1 | Injector cylinder 1 |
| A15 | Lowside 2 | Injector cylinder 2 |
| A4 | Lowside 3 | Injector cylinder 3 |
| A16 | Lowside 4 | Injector cylinder 4 |
| A5 | Lowside 5 | Injector cylinder 5 |
| A6 | Lowside 6 | Injector cylinder 6 |
| A7 | Lowside 7 | Injector cylinder 7 |
| A19 | Lowside 8 | Injector cylinder 8 |
| A35 | Ign 1 | Cyl 1 logic coil |
| A34 | Ign 2 | Cyl 2 logic coil |
| A22 | Ign 3 | Cyl 3 logic coil |
| A33 | Ign 4 | Cyl 4 logic coil |
| A32 | Ign 5 | Cyl 5 logic coil |
| A31 | Ign 6 | Cyl 6 logic coil |
| A30 | Ign 7 | Cyl 7 logic coil |
| A29 | Ign 8 | Cyl 8 logic coil |
| C20 | Analog Temp 3 | CLT |
| C30 | Analog Temp 2 | IAT |
| C13 | Analog Volt 1 | MAP 0–5 V |
| C24 | Analog Volt 2 | TPS 1 |
| C34 / C35 | Knock 1 / Knock 2 | Knock, one per bank |
| A20 | Lowside 10 | Fuel-pump relay coil |
| A21 | Lowside 12 | Main-relay coil |
| A12 | Lowside 15 | Radiator-fan relay coil |
| B17 / B16 | CAN 1 H / L | Dash / wideband |
| B18 | Battery Sense | Ignition-switched 12 V (5 A fuse) |
| B23 | +12 V MR | Main-relay 12 V into ECU |
| A17 A18 A24 B14 B19 B20 | Power GND | Engine block → battery − |
| C9 / C21 / C32 | 5 V Sens 1 | MAP, TPS, pedal 1 |
| C1–C8, C29, C31 | Sensor GND | 0–5 V and thermistor returns |
Trigger
Optispark is an optical disc in the cover, driven off the cam. It is not GM_24x and not a 36-1. Water under that cover is why people convert them. Convert the crank, do not debug a drowned disc and call it a decoder.
Crank
| Factory | Unsupported named mode. |
| Conversion | 36-1 Hall or VR, or a 24x wheel that is actually a 24x. |
Cam
| Sequential | Digital 2 after the conversion. The Optispark high-resolution track is not the cam input to wire “just in case”. |
TunerStudio
| Setting | Value |
|---|---|
| Trigger / wheel type | 36-1 + cam, or GM 24x only with a 24x wheel. Not Optispark |
| Use only rising edge | VR: typically yes on MAX992x. Hall: as logged |
| Invert primary | No — swap VR wires first |
| Firing order | 1-8-4-3-6-5-7-2 |
Offset: Light on cylinder 1, front of the left bank. If you converted to COP, the cap is gone and the software order is the only order.
Injection
Eight high-Z port injectors. Later LT1 PCMs are sequential; earlier are batch. Race Core can run them sequential after a cam sync. Meter the injectors. A 24 lb LT1 injector is not an LS3 number.
| Impedance | High-Z. Saturated drivers. |
Ignition
Optispark still in place: one coil, Ign 1 into an igniter, module and coil pins TBD. The cap does the distribution, so firing order is mechanical until you remove the cap. COP conversion: Ign 1–8 by cylinder number, small-block firing order in software, logic coil dwell 2.0–2.5 ms (longer for an LS truck coil, per the LS1 note, if that is the coil you fitted).
| LS order | 1-8-7-2-6-5-4-3 is the wrong crank. |
Idle
Cable throttle and a stepper or PWM IAC. A bipolar stepper uses the F7 H-bridges. PWM idle pin is TBD. No DBW on a 1992–1997 LT1.
First start
- Load the matching variant configuration in TunerStudio before the harness is live — injectors and coils stay disconnected until the decoder is confirmed.
- Fuel pump fuse out. Coils unplugged or spark outputs disabled. Crank. Open Diagnostics → composite / high-speed logger.
- Confirm crank teeth are even, the missing-tooth (or named pattern) is a single clean gap, and cam is one pulse per two crank revolutions for sequential four-stroke.
- RPM during cranking should sit in the 150–350 rpm band. 0 rpm or 12,000 rpm means the decoder is lost — polarity or wheel type, not offset.
- Lock timing to a fixed 10° (idle control off). Timing light on cylinder 1. Change trigger offset until the damper agrees with 10°.
- Recheck at ~3,000 rpm. If timing walks with RPM, it is VR polarity, a delayed Hall, or the wrong decoder — not offset.
- Enable spark. Confirm a healthy burn (timing light or plug colour) with fuel still disabled.
- Enable fuel. Prime, then crank. Catch the first idle on a rich-safe VE, then lean toward stoich at idle.
- Only then enable closed-loop idle, VVT, boost and traction. A base map is a starting point, not a dyno tune.
A base map is a starting point, not a dyno tune.