If your engine cranks but the ECU sees nothing, the trigger system is the first place to look. Crank and cam timing sensors are the ECU's only way of knowing where the engine is in its cycle. Get the reluctor ring wrong, wire the sensor incorrectly, or mix up a 24x and 58x trigger wheel, and the ECU cannot calculate injector timing or ignition advance. The engine will not run. This post covers the specific reluctor ring designs used by LS, LT, and Coyote engines, why each matters for ECU recognition, and the wiring and installation errors that catch builders out.

Why the trigger system is non-negotiable

The ECU uses the crankshaft position sensor to count teeth on the reluctor ring and establish engine speed and position. The cam sensor tells it which stroke the engine is on. Together they give the ECU everything it needs for sequential injection and coil-per-cylinder ignition. Without a clean, correctly configured trigger signal, even the best standalone ECU is blind.

The reluctor ring tooth count is not interchangeable. Each engine family uses a specific pattern, and the ECU firmware is written to recognise that pattern. Fit the wrong ring, use the wrong sensor gap, or feed the signal through excessive electrical noise, and you get misfires, no-starts, or erratic timing at best.

For anyone working through an engine swap build, the Haltech ECU for Engine Swaps: A Builder's Guide to the Range and Sensors post covers which ECU trigger input modes apply to each popular swap and is worth reading alongside this one.

LS engines: 24x crank, 1x cam

Gen III LS engines (LS1, LS6) use a 24-tooth reluctor wheel on the crankshaft with a single-tooth cam reluctor on the camshaft. The crank sensor reads 24 evenly spaced teeth per revolution. The cam sensor reads one tooth per two revolutions of the crank, which tells the ECU which bank is on the compression stroke.

The 24x pattern is well-supported by aftermarket ECUs. Haltech, MegaSquirt, and AEM all have a 24x trigger mode. Most standalone systems can also decode the reluctor ring signal from a Gen IV 58x crank (more on that below), so if you are running a Gen III bottom end with a Gen IV head combination, confirm which crank reluctor ring is physically present before configuring the ECU.

OEM vs aftermarket reluctor rings. On LS swaps where the original crank reluctor has been damaged or where a custom crankshaft is used, billet aluminium replacement rings are available. The tooth profile must match the OEM specification exactly. A tooth that is too wide or too narrow will cause the sensor to misread the gap between teeth, generating a false position signal. If you use a billet ring, source one that is machined to the correct OEM tooth geometry, not a generic pattern.

Sensor gap. The LS crank sensor is a magnetic variable-reluctance (VR) type on Gen III applications. The air gap between the sensor tip and the reluctor teeth should be 0.5 mm to 1.5 mm [VERIFY]. Too large a gap reduces signal amplitude at low cranking speeds and the ECU may not see enough signal to trigger. Too small a gap risks the sensor contacting the ring under thermal expansion.

Common LS wiring errors. VR sensors produce a sine-wave output, not a square wave. If the ECU input is configured for a Hall-effect sensor (square wave), the trigger will not be recognised. Always check whether the sensor is VR or Hall before setting the input type in the ECU calibration.

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LT engines: 58x crank, 4x cam

Gen V LT engines (LT1, LT4, LT1 truck) use a 58-tooth reluctor wheel on the crank with a missing tooth at the sync gap, and a 4x cam pattern. The 58x system gives the ECU much higher angular resolution than 24x: one tooth every 6 degrees of crank rotation instead of 15 degrees. That resolution matters for direct injection timing and cylinder deactivation, both of which LT engines use from the factory.

The cam sensor on an LT runs a 4-tooth pattern. This gives the ECU more data points per cycle compared to the single LS cam tooth, which helps with faster sync at startup.

Mixing Gen III and Gen V parts. It is possible to run a Gen III 24x bottom end with an LT-based ECU or vice versa, but the ECU must be configured to match the ring actually fitted to the crankshaft. Running an LT ECU calibration against a 24x reluctor ring will result in a no-start because the ECU is counting 58 teeth that are not there. This is a more common mistake than it sounds, particularly on engine combinations assembled from a mix of donor parts.

Hall-effect sensors on LT applications. Gen V LT crank sensors are Hall-effect devices, not VR sensors. They need a supply voltage (typically 5V or 12V depending on the sensor) and produce a clean digital square wave. The wiring is three-wire: power, ground, and signal. If you are retrofitting an LT engine into a chassis that previously ran an LS, do not assume the sensor wiring is compatible. Check the sensor type and configure the ECU input accordingly.

Coyote engines: 36-1 crank, variable cam

Ford's Coyote V8 (5.0 Ti-VCT) uses a 36-minus-1 reluctor pattern on the crank: 35 evenly spaced teeth and one gap. The missing tooth is the reference point the ECU uses to establish absolute crank position. This is a widely used pattern in the aftermarket and most standalone ECUs support it natively.

The cam timing sensor setup on the Coyote is more involved than on the LS because the engine uses Twin Independent Variable Cam Timing (Ti-VCT) on both intake and exhaust camshafts. Each cam has its own sensor and phaser. A standalone ECU that does not support variable cam timing control will need to lock the phasers mechanically or via a dedicated cam control strategy. Running the Coyote with unpinned phasers and no cam control can result in erratic idle and inconsistent timing.

Gen 1 vs Gen 2 Coyote cam patterns. The Gen 1 Coyote (2011 to 2014) and the Gen 2 (2015 onwards) differ in their cam trigger pattern. The Gen 2 uses a revised cam tooth arrangement, and some aftermarket ECUs require a different trigger offset setting. Confirm the engine year before setting up the ECU trigger configuration, and cross-reference with the ECU manufacturer's trigger library.

Crank sensor type. The Coyote crank sensor is a VR type. It generates a sine-wave signal, so the ECU input must be set to VR mode, not Hall. This is one of the cam timing sensor with a Coyote ECU mistakes that appears regularly on forum threads: the builder uses a Hall-effect input on a VR sensor, sees intermittent or absent trigger signals, and chases a wiring fault that does not exist.

DIY reluctor ring installation

If you are fitting a new or replacement reluctor ring, the process is straightforward but the tolerances are tight.

1. Confirm the tooth count. Measure the ring against the OEM specification before pressing it onto the crank. Count the teeth. It sounds obvious, but misidentified parts are common when buying from surplus or used stock.

1. Phasing. The ring must be clocked correctly relative to the crankshaft keyway. The missing tooth (or sync tooth on single-tooth cam patterns) has a specific angular relationship to TDC. Fit the ring in the wrong orientation and the ECU will calculate position from a reference that is offset by a fixed amount, which shows up as timing error across the rev range.

1. Interference fit. Billet rings are typically pressed onto the crank snout or crankshaft flange. Use the correct press fit and confirm the ring is square before pressing fully home. A ring that is cocked on the shaft will produce variable tooth spacing as it rotates, generating false crank signals.

1. Sensor gap check. After installation, set the sensor gap with the crank at the normal operating temperature if possible, or account for thermal expansion in the gap setting. A gap set cold on an aluminium ring will close up as the engine reaches operating temperature.

Wiring and shielding for trigger sensors

Trigger sensor signals are low-amplitude and run at relatively low voltage. They are susceptible to interference from ignition systems, alternators, and any other high-current circuits nearby. This is not a wiring problem to sort out after the first start. It needs to be correct before the engine runs.

The sensor signal wire should be shielded, with the shield grounded at the ECU end only. Grounding both ends creates a ground loop that can inject noise into the signal. Twisted-pair shielded cable is the standard choice for both VR and Hall-effect sensor circuits.

Keep trigger sensor wiring away from ignition wires. Running a cam sensor wire alongside a coil wire for 300 mm is a reliable way to introduce enough interference to generate phantom trigger events. Route sensor wiring on the opposite side of the engine bay where possible.

For detailed guidance on gauge, shielding, and termination standards for the full sensor harness, see the Haltech Harness Wiring: Gauge, Shielding, and Connector Standards for a Reliable First Start post.

ECU configuration checklist before first start

Before cranking, confirm the following in the ECU calibration:

• Trigger wheel type set to match the physical ring: 24x for Gen III LS, 58x for Gen V LT, 36-1 for Coyote.
• Sensor type set correctly: VR for Gen III LS crank, Hall for Gen V LT crank, VR for Coyote crank.
• Cam sensor mode configured for the correct tooth count and pattern.
• Trigger offset set to a known starting value for the engine family. First start values are published in most ECU manufacturer trigger libraries.
• Sync source configured if the ECU requires explicit assignment of the cam sensor as the sync input.

A scope or a digital multimeter with oscilloscope function is worth using to verify the crank and cam signals are present and clean before attempting to start. The signal should show consistent amplitude and tooth spacing. Irregular spacing, missing teeth, or signal dropout during cranking all need to be resolved before tuning can begin. See the LS Swap ECU Tuning Guide: DIY vs. Dyno and Where Builders Go Wrong for what comes next once the trigger system is confirmed.

Gauges, data logging, and trigger signal monitoring

Once the engine is running, a dash with CAN bus support will let you monitor engine speed and cam timing values in real time. If the ECU is reporting cam timing that is erratic or drifting at steady throttle, the trigger system is still the first suspect. Browse the Gauges & Instrumentation collection for Haltech and AEM display units that work directly with common standalone ECUs over CAN.

For ignition system components including sensors, wires, and related hardware, the Ignition collection covers the MSD and ACCEL range commonly used alongside aftermarket ECUs on V8 swaps.