Speeduino First Start and Sync-Loss Troubleshooting

A Speeduino first start should be the end of a commissioning process, not the beginning of troubleshooting. By the time the engine is allowed to receive fuel and spark, the ECU should already have stable communications, calibrated sensors, correct injector and ignition channel mapping, a clean trigger pattern and a mechanically verified ignition reference.

If the engine still refuses to start, separate the problem into two categories: the ECU is synchronized but the engine does not run, or the ECU is losing engine-position sync. Those are completely different faults.

Current Speeduino firmware tracks a sync-loss counter, supports high-speed tooth/trigger logging and explicitly stops normal fuel/ignition processing when crank/cam synchronization is lost. That makes sync diagnosis much easier than guessing from the sound of the starter.

First Start Should Not Be the First Time You Check Anything

Before the first real start attempt, you should already have completed the bench and cranking checks from the earlier guides.

Correct Speeduino firmware and matching TunerStudio INI.
TPS calibrated and moving smoothly from closed to wide open.
CLT and IAT showing plausible temperatures.
MAP showing roughly atmospheric pressure with the engine stopped.
Battery voltage in TunerStudio matching a multimeter reasonably closely.
Injector outputs mapped to the intended cylinders/groups.
Ignition outputs mapped and polarity verified.
Crank/cam decoder selected correctly.
Tooth/trigger log clean during cranking.
Fixed ignition timing checked with a timing light.
Fuel pressure verified mechanically.

If any of those items are still unknown, fix them before changing VE, cranking fuel or ignition tables.

A Useful First-Start Decision Tree

Engine cranks
   │
   ├── No RPM shown
   │      └── crank sensor / wiring / conditioner / decoder input
   │
   ├── RPM shown but no sync
   │      └── decoder / edge / missing tooth / cam phase / noise
   │
   ├── Sync stable, no spark
   │      └── ignition output / coil / dwell / polarity / channel mapping
   │
   ├── Sync stable, no injector pulse
   │      └── injection config / channel mapping / driver / enable state
   │
   ├── Spark + fuel but no start
   │      └── timing / fuel pressure / pulse width / firing order / compression
   │
   └── Starts then dies
          └── after-start / idle / fuel / sync / voltage / sensor issue

No RPM While Cranking

If TunerStudio shows zero RPM, Speeduino is not seeing a usable primary trigger signal.

Crank sensor not powered or not connected.
VR sensor gap too large.
VR polarity or conditioner path wrong.
Hall sensor missing pull-up or wrong supply.
Primary trigger routed to the wrong ECU pin.
Wrong board jumper/input mode.
Sensor mechanically too far from the trigger wheel.

Do not enable fuel and spark until the ECU can show stable, plausible cranking RPM.

RPM but No Sync

An apparent RPM value does not prove the ECU knows engine position. Speeduino can sometimes estimate RPM from incoming transitions while still failing to identify the pattern correctly.

If RPM exists but sync is unstable, investigate:

Wrong trigger decoder.
Wrong nominal tooth count or missing-tooth count.
Primary trigger edge wrong.
VR sensor polarity reversed.
Cam/secondary edge wrong.
Cam event occurring in an unexpected phase window.
Noise creating an extra tooth.
Missing real tooth due to weak signal.

The sync-loss counter should stay still once the decoder is synchronized. A counter that increments while cranking or running tells you the ECU is repeatedly losing position information.

What the Sync-Loss Counter Tells You

The current Speeduino TunerStudio definition exposes syncLossCounter as a status channel. Watch it during cranking and while the engine runs.

Observation	Interpretation
Counter stays at zero	No recorded sync-loss events in that session
Counter rises during cranking	Trigger pattern is unstable before start
Counter rises only when coils fire	Ignition noise / grounding / trigger interference likely
Counter rises above a specific RPM	Signal conditioning, sensor gap, edge or high-frequency issue
Counter rises when starter disengages	Transient/noise or decoder transition issue

Use the Tooth Logger Before Touching Fuel

A missing-tooth wheel should show a repeatable long gap in the tooth log. The normal tooth intervals vary during cranking because engine speed is not constant, but the pattern should still be recognizable.

Conceptual 36-1 log:

| | | | | | | |    | | | | | | |
                ^^^
             missing gap

Bad log:
| | || | |     | | |  || | |
    ^^                 ^^
 extra pulses / noise

If the tooth log is wrong, fuel-table changes are irrelevant. The ECU does not know where the engine is.

Composite / Trigger Logging for Cam-Sync Systems

Sequential configurations need the secondary cam signal to arrive in the expected relationship to the crank pattern. Use the composite/trigger logger to compare primary and secondary events.

If the crank pattern is clean but full sequential sync never appears, focus on the cam signal, edge, phase and decoder configuration.

Cranking RPM Should Be Plausible

A normal passenger-car engine may crank somewhere around a few hundred RPM; motorcycles and small engines vary considerably. What matters is that the reading is stable and believable.

If the real starter sounds steady but TunerStudio jumps between 150 RPM and 4000 RPM, that is not an engine-speed problem. It is a trigger-signal problem.

Weak Battery Can Create Trigger Problems

A weak battery creates several problems at once:

Starter RPM falls.
VR sensor output amplitude falls.
Battery voltage at the ECU falls.
Injector opening time increases.
Coil charge behaviour changes.
Electrical noise relative to signal amplitude becomes worse.

Do not diagnose a marginal trigger system with a nearly flat battery. Charge the battery or use a suitable support supply before collecting logs.

Cranking with Fuel and Spark Disabled

Before the first firing attempt, crank the engine with fuel and/or ignition disabled as appropriate and verify:

Stable RPM.
Stable sync.
No sync-loss counter increments.
Reasonable MAP movement.
Battery voltage does not collapse.
Oil pressure develops if the engine/build requires that check.

This isolates the crank/cam system from ignition noise and combustion effects.

Then Add Ignition

Once crank-only sync is stable, enable ignition while keeping fuel disabled where practical.

Watch the sync-loss counter again. If the trigger was perfect with coils disabled but immediately becomes unstable when coils fire, you have probably found an electrical-noise or grounding problem.

Coil primary wires too close to crank/cam harness.
Ignition grounds sharing sensitive sensor returns.
Poor ECU ground.
Unshielded trigger wiring.
Wrong smart-coil logic ground arrangement.
External igniter ground or flyback issue.

Fixed Timing Is Mandatory

Before letting the ignition table control timing, command a fixed ignition angle and check it mechanically with a timing light.

TunerStudio fixed timing = 10° BTDC

Timing light should show:
10° BTDC on the real crank mark

If it does not, fix trigger angle/reference, decoder settings, sensor edge or channel mapping. Do not reshape the ignition table to hide a trigger-reference error.

Check Timing at More Than One RPM

A timing mark that is correct at cranking speed but drifts as RPM rises can indicate:

VR polarity problem.
Wrong trigger edge.
Conditioner threshold/zero-crossing behaviour.
Mechanical trigger-wheel movement.
Incorrect decoder/reference configuration.

Verify fixed timing at idle and a moderate RPM before trusting the ignition system.

Then Add Fuel

Once sync and ignition reference are proven, enable fuel.

Before cranking, verify rail pressure with a real gauge. Do not assume hearing the pump means the system has correct pressure.

Fuel Pressure Before First Start

Injector flow data is only valid at the intended differential fuel pressure. For a typical port-injection system, confirm:

Pump primes.
No fuel leaks.
Rail pressure reaches the regulator target.
Pressure does not collapse immediately.
Boost-referenced regulator hose is connected correctly if used.

A no-start caused by 1 bar of fuel pressure will not be fixed by adding 50% cranking enrichment.

Injector Pulse Exists — but Is Fuel Actually Entering the Engine?

TunerStudio can show injector pulse width while a blocked injector, dead driver, disconnected supply or empty rail delivers no fuel.

Useful checks include injector click/noid testing, driver output verification and spark-plug inspection after a brief crank attempt. Perform fuel tests safely and avoid open fuel spray around ignition sources.

Dry Plugs vs Wet Plugs

Spark-plug condition after cranking	Likely direction
Bone dry	No fuel delivery, no injector command, low pressure or blocked injectors
Wet with fuel	Possible flooding, no spark, wrong timing or excessive cranking fuel
Normal fuel smell but no fire	Check spark energy, timing and compression

Do Not Keep Cranking a Flooded Engine

Repeated failed start attempts can fill the cylinders and foul plugs. Once plugs are wet, the engine may continue refusing to start even after the original problem has been fixed.

Stop, clear the excess fuel according to a safe procedure, dry or replace fouled plugs and then resume diagnosis.

Verify Firing Order and Channel Mapping

An engine can have strong spark, correct fuel pressure and perfect sync yet never start if the coils or injectors are assigned to the wrong cylinders.

Check both the engine firing order and the Speeduino output sequence. Wasted-spark pairings must also be correct.

Spark at the Plug Is Not Enough

A plug may spark in free air but fail under cylinder pressure. Weak coil supply, poor dwell, excessive plug gap or a marginal igniter can all produce this behaviour.

However, on a fresh Speeduino install, verify timing and channel mapping before assuming the spark is simply ‘too weak’.

Starts but Dies Immediately

If the engine fires and then stops after one or two seconds, first distinguish between sync loss and fueling/idle control.

What happens	Likely area
Sync-loss counter increments	Trigger/cam/noise problem
RPM falls smoothly with sync intact	Fuel/air/idle problem
Starts only while throttle is open	Idle-air / throttle / fueling
Starts then floods	Cranking/after-start fuel too rich or injector config wrong
Starts then leans out	Fuel pressure / required fuel / after-start correction

Cranking Fuel Is Not the VE Table

During cranking, Speeduino applies dedicated cranking fuel and enrichment logic. If an engine will not start, do not immediately rewrite the normal VE table.

First prove injector flow data, fuel pressure, cranking pulse behaviour and sensor values.

Coolant Temperature Can Ruin First-Start Fueling

If CLT calibration is wrong and the ECU thinks a 20°C engine is at -40°C, warm-up/cranking enrichment can become wildly excessive. If it thinks a cold engine is already hot, there may be too little fuel.

Compare CLT and IAT readings to actual ambient/engine temperature before cranking.

MAP and TPS Must Be Plausible

A MAP sensor reading far from atmospheric pressure with the engine stopped usually indicates wrong calibration or wiring. TPS should sit near the calibrated closed value and move smoothly.

Bad load inputs can distort fueling and acceleration enrichment during the very first start attempt.

Wideband Is Not Useful Until It Is Ready

A wideband sensor/controller needs to warm up. Do not interpret an unheated or faulted wideband value as real combustion AFR.

Once the engine is running steadily and the wideband is ready, use lambda/AFR to guide tuning—not during the first half-second of an unstable start.

Engine Starts but Sync Is Lost When RPM Rises

This is a classic trigger-system fault.

VR conditioner ringing or saturation.
VR polarity wrong.
Hall pull-up too weak.
Trigger filter settings inappropriate.
Sensor gap/runout problem.
Noise increases with ignition frequency.
60-2 or high-tooth-count signal becoming marginal at speed.

Capture a tooth log immediately before/through the breakup if possible.

Engine Syncs at High RPM but Not While Cranking

That usually points toward a weak low-speed signal rather than excessive high-speed noise.

VR sensor gap too large.
Weak VR sensor.
Conditioner threshold too high.
Starter speed too low.
Battery voltage collapsing.
Hall sensor not switching cleanly at low target speed/gap.

Sync Loss Only When the Starter Disengages

The electrical and mechanical environment changes abruptly when the starter motor releases. A transient, ground shift or sudden RPM change can expose a marginal trigger configuration.

Check starter wiring/grounds, battery voltage log and the exact tooth pattern around the event.

Sync Loss When Injectors Are Enabled

Injectors are inductive loads and can inject noise into the harness if driver flyback, grounding or wiring is poor.

If crank-only and ignition-only tests are stable but enabling injectors creates sync loss, inspect injector power routing, ECU power grounds and trigger-harness separation.

RPM Spike Followed by Engine Cut

A false trigger edge can make the ECU calculate an impossible instantaneous RPM. The decoder may then lose sync and Speeduino stops normal scheduling until position is re-established.

Treat an impossible RPM spike as signal evidence, not as a real engine acceleration.

RPM Drops to Zero for One Instant

A brief zero-RPM event can occur when the ECU stops receiving valid trigger events or loses sync badly enough that engine rotation is considered stopped.

Look at the tooth/trigger log and sync-loss counter rather than the dashboard gauge alone.

Trigger Filtering: Use Carefully

Speeduino supports trigger filtering strategies, but filtering is not a replacement for a clean electrical signal.

An aggressive filter that removes ignition noise at 2000 RPM may also reject real teeth at 7000 RPM. Fix sensor polarity, wiring, grounding and conditioner behaviour first.

Mechanical Problems Can Mimic ECU Problems

Cam timing one tooth out.
Very low compression.
Incorrect valve clearances.
Major intake leak.
Distributor installed out of phase.
Trigger wheel mechanically slipped.

If spark, fuel and timing are all proven but the engine still does not attempt to fire, perform basic mechanical checks rather than assuming the tune is uniquely at fault.

Do Not Copy Somebody Else’s First-Start Tune Blindly

A tune from the same engine family can still have different injector flow, dead time, fuel pressure, trigger angle, MAP sensor, ignition coils, camshafts or compression ratio.

Use known-good data as a reference, not as proof that every configuration field is correct for your hardware.

Save Logs from Every Failed Attempt

A short TunerStudio datalog is much more useful than remembering that the engine ‘nearly started’.

For each attempt, log at least:

RPM.
Sync-loss counter.
Battery voltage.
MAP.
TPS.
CLT/IAT.
Injector pulse width.
Ignition advance.
Lambda/AFR when valid.

Pair the datalog with a tooth/trigger log when the fault smells like synchronization.

A Good First-Start Sequence

Check all fluid levels and mechanical readiness.
Verify ECU power and grounds.
Confirm sensor calibrations.
Verify fuel system for leaks with pump running.
Crank with fuel and ignition disabled; prove stable sync.
Enable ignition only; re-check sync and fixed timing.
Enable fuel; verify pressure and injector operation.
Attempt a short start.
If it does not start, stop and review logs instead of cranking continuously.
If it starts, stabilize idle only enough to verify oil pressure, coolant temperature, AFR and sync.
Save the first successful datalog and tune immediately.

What Not to Adjust First

Do not reshape the whole VE table.
Do not add huge cranking enrichment because the engine did not fire once.
Do not change trigger edges randomly.
Do not increase coil dwell blindly.
Do not disable filtering/safety features without understanding the fault.
Do not ignore a rising sync-loss counter because the engine ‘sort of runs’.

When the Engine Finally Starts

The first successful start is not the time for full-load tuning. Keep it short and controlled.

Check oil pressure immediately.
Watch coolant temperature.
Watch lambda/AFR once the wideband is ready.
Watch battery/charging voltage.
Watch sync-loss counter.
Check for fuel, coolant and oil leaks.
Listen for abnormal mechanical or ignition noise.

Only after the engine can start, idle and rev lightly with stable sync should normal VE and ignition tuning begin.

Final Troubleshooting Matrix

Symptom	First place to look
No RPM	Primary trigger hardware/input
RPM but no sync	Decoder, tooth count, edge, cam phase
Sync counter rises with coils	Ignition noise/grounds/harness
Sync counter rises above certain RPM	Sensor/conditioner/filter/edge
Stable sync, no spark	Ignition output, polarity, dwell, coil supply
Stable sync, no fuel	Injector driver, pressure, configuration
Spark + fuel, no start	Fixed timing, firing order, compression, flooding
Starts then dies with sync intact	Fuel/idle/after-start settings
Starts then dies with sync loss	Trigger/cam/noise problem

Final Recommendation

Treat the first Speeduino start as a sequence of proofs. First prove crank/cam synchronization. Then prove ignition timing mechanically. Then prove fuel pressure and injector operation. Only after those three systems are known-good should you tune fuel tables.

If the sync-loss counter increases, stop tuning and fix the trigger system. Speeduino’s firmware depends on reliable crank/cam synchronization and will not schedule fuel and ignition correctly when engine position is uncertain.

The fastest troubleshooting workflow is usually: look at the sync-loss counter, capture a tooth/trigger log, verify fixed timing, verify fuel pressure, then inspect the normal datalog. That turns a vague no-start into a finite set of testable faults.

Related Speeduino Guides

Official Speeduino Resources

Speeduino Manual — installation, wiring and tuning documentation.
Speeduino TunerStudio INI — includes current status channels such as sync-loss counter.
Speeduino Firmware Repository — current synchronization, trigger logging and engine-control code.
Speeduino Ardu-Stim — crank/cam pattern simulator for bench testing.