# Megasquirt Comprehensive Tuning Guide

## Pre-Tuning Checklist

### Mechanical Verification
- [ ] Engine compression tested and within spec
- [ ] Valve lash adjusted correctly
- [ ] Timing belt/chain properly aligned
- [ ] No vacuum leaks (intake manifold, hoses, PCV)
- [ ] Fuel pressure verified at regulator
- [ ] Fuel filter clean
- [ ] Injectors flowing evenly
- [ ] Spark plugs gapped and in good condition
- [ ] Ignition wires/coil packs functioning
- [ ] All sensors reading correctly

### Electrical Verification
- [ ] Battery fully charged (>12.4V)
- [ ] Alternator charging properly
- [ ] Megasquirt grounds clean and tight
- [ ] Injector harness polarity correct
- [ ] Coil wiring correct
- [ ] Sensor wiring verified with multimeter
- [ ] Wideband O2 powered and heated

## Initial Startup Procedure

### First Start Preparation
1. Load conservative base tune
2. Set required fuel for your injectors
3. Set cranking pulse widths (typically 2-5ms)
4. Verify timing with light before cranking
5. Prime fuel system, check for leaks
6. Have fire extinguisher ready

### Cranking Settings
**Cranking RPM Threshold**: 300 RPM (below this = cranking mode)

**Cranking Pulse Widths:**
- Cold (-20°C): 8-15ms
- Warm (20°C): 4-8ms
- Hot (70°C): 2-4ms
- Adjust based on injector size and engine needs

**Prime Pulse:**
- 1-3ms at key-on
- Helps first start
- Don't flood engine

### Post-Start Verification
1. Oil pressure builds within 5 seconds
2. No unusual noises
3. Coolant circulating
4. AFR gauge responding
5. All sensors reading reasonable values

## Idle Tuning Procedure

### Step 1: Mechanical Idle
1. Disconnect idle valve or set to manual control at 0%
2. Adjust throttle stop screw for 400-500 RPM (below target)
3. This ensures throttle plate isn't controlling idle

### Step 2: Minimum Airflow
1. Enable idle valve
2. Set closed-loop idle control
3. Target 50-100 RPM below desired idle
4. Adjust minimum duty for stability

### Step 3: VE Table at Idle
1. Target AFR: 13.5-14.0
2. Adjust VE until AFR matches target
3. EGO correction should be near 0%
4. Note: Some engines prefer richer idle (13.0-13.5)

### Step 4: Idle Advance
1. Start with 15-20° BTDC
2. More advance can improve stability
3. Too much advance causes roughness
4. Typical range: 15-25°

### Step 5: Idle Valve Tuning
- **Closed Position**: PWM for hot idle (20-40%)
- **Open Position**: PWM for cold start (60-80%)
- **Cranking Position**: PWM during start (50-70%)
- Adjust curve between these points

### Step 6: Closed-Loop PID
Start conservative:
- **P (Proportional)**: 20-50
- **I (Integral)**: 10-30
- **D (Derivative)**: 0-10

Increase P until oscillation, then back off.
Add I to eliminate steady-state error.
Use minimal D (can cause instability).

## Fuel Table Tuning

### Tuning Order Priority
1. Idle region (600-1200 RPM, 30-50kPa)
2. Light cruise (1500-2500 RPM, 40-60kPa)
3. Part throttle acceleration
4. Highway cruise
5. WOT tuning
6. High RPM/load

### Steady-State Tuning Method
1. Warm engine fully (CLT > 80°C)
2. Select fixed gear (dyno or long straight road)
3. Hold RPM/load cell for 3-5 seconds
4. Allow EGO correction to stabilize
5. Note correction percentage
6. Adjust VE by inverse of correction

Example:
- Current VE: 60
- EGO correction: +12%
- New VE: 60 × 1.12 = 67

### AFR-Based Calculation
```
New VE = Current VE × (Target AFR / Measured AFR)
```

Example:
- Target: 14.0
- Measured: 12.5 (rich)
- Current VE: 70
- New VE: 70 × (14.0/12.5) = 78.4

### Transition Tuning
Cells between steady-state points:
- Interpolate between tuned cells
- Test during actual driving
- Fine-tune if transition feels rough

## Ignition Timing Tuning

### Base Timing Verification
1. Disconnect injector connector (prevents starting)
2. Set fixed timing in software (usually 10° or 15°)
3. Crank engine with timing light
4. Verify light shows set advance
5. Adjust trigger angle if offset
6. Re-enable variable timing

### Conservative Starting Point
| RPM \ kPa | 20 | 40 | 60 | 80 | 100 |
|-----------|----|----|----|----|-----|
| 800       | 20 | 18 | 15 | 12 | 10  |
| 1500      | 35 | 30 | 25 | 20 | 15  |
| 2500      | 40 | 35 | 30 | 25 | 20  |
| 4000      | 42 | 38 | 32 | 28 | 22  |
| 6000      | 45 | 40 | 35 | 30 | 25  |

### Tuning for Power
1. Start with conservative map
2. Increase timing 2° at a time in target cells
3. Dyno or acceleration test each change
4. Stop when no more power gained
5. Back off 2° for safety margin

### Knock Detection
Listen for:
- Pinging/rattling under load
- Loss of power
- Elevated EGT

If knock detected:
- Reduce timing immediately
- Add fuel in affected area
- Check for hot spots, carbon buildup
- Verify fuel quality (octane rating)

## Acceleration Enrichment

### TPS-Based Enrichment
**When to use**: Most applications with cable throttle

**Settings:**
- **Threshold**: 5-10%/second TPS rate
- **Enrichment**: 10-25% added fuel
- **Decay**: 0.5-1.5 seconds

**Tuning Procedure:**
1. Start with conservative settings
2. Perform tip-in from steady cruise
3. Watch AFR: Should briefly richen (0.5-1.0 lambda)
4. If lean spike (>1.1 lambda), increase enrichment
5. If no lean spike but bog, reduce enrichment
6. Too rich causes hesitation and black smoke

### MAP-Based Enrichment
**When to use**: Individual throttle bodies, ITBs

**Settings:**
- **Threshold**: 20-50 kPa/second
- **Enrichment**: Scales with MAPdot

**Tuning similar to TPS-based**

### Cold Accel Multiplier
Increases enrichment when engine is cold:
- -20°C: 2.0-3.0×
- 0°C: 1.5-2.0×
- 20°C: 1.2-1.5×
- 60°C+: 1.0× (no extra)

### Decay Rate
- Too fast: Bog returns after initial tip-in
- Too slow: Rich surge continues
- Target: Just covers the transient event

## Warmup Enrichment

### Afterstart Enrichment
- **Duration**: 50-200 engine cycles
- **Initial**: 20-40% extra fuel
- **Taper**: Linear to 0% over duration

### Warmup Enrichment Curve
| Coolant Temp | Enrichment |
|--------------|-----------|
| -40°C        | 180%      |
| -20°C        | 160%      |
| 0°C          | 140%      |
| 20°C         | 120%      |
| 40°C         | 110%      |
| 70°C         | 100%      |
| 80°C+        | 100%      |

### Tuning Warmup
1. Cold start engine
2. Monitor AFR during warm-up
3. Should be slightly rich (12-13 AFR)
4. Smoothly transition to 14.7
5. Adjust curve if too lean or rich at specific temps

## Deceleration Fuel Cut (DFCO)

### Purpose
- Save fuel during deceleration
- Reduce emissions
- Prevent afterfire in exhaust

### Settings
- **TPS Threshold**: <5-10%
- **RPM Threshold**: 200-500 RPM above idle
- **MAP Threshold**: <30-40 kPa (high vacuum)

### Re-Enable Conditions
- TPS rises above threshold
- RPM drops to threshold
- MAP rises above threshold

### Tuning
- Enable if popping/backfiring on decel
- Disable if causing hesitation when returning to throttle
- Add taper for smooth re-enable

## Boost Control (Turbo/Supercharged)

### Open Loop Boost Control
1. Create duty cycle table vs RPM
2. Start conservative (low duty = low boost)
3. Increase duty in 5% increments
4. Target boost level at each RPM
5. Log boost vs duty for each gear

### Closed Loop Boost Control (if available)
**PID Tuning:**
- Start with P=10, I=0.1, D=0
- Increase P until oscillation, back off
- Add I to eliminate steady-state error
- Use minimal D

**Target Boost Table:**
- Low RPM: Minimize boost (spool)
- Mid RPM: Target boost level
- High RPM: May taper to prevent over-speed

### Overboost Protection
- Set fuel/ignition cut above target
- Margin: 1-3 PSI above target boost
- Prevents engine damage

## Launch Control

### Settings
- **Launch RPM**: 4000-6000 (engine dependent)
- **Retard Timing**: 0-10° BTDC during launch
- **Fuel/Ignition Cut**: Hard limit method

### Flat Shift
- Maintain throttle during shifts
- Brief cut (100-200ms) at shift point
- Retains boost between gears

## Troubleshooting Common Issues

### Hard Starting
- Cranking PW too lean/rich
- No spark during cranking
- Trigger issue (no RPM signal)
- Fuel pump not priming

### Idle Instability
- Vacuum leaks
- Incorrect TPS calibration
- EGO correction too aggressive
- Ignition timing fluctuating
- Mechanical issues (valves, compression)

### Hesitation on Acceleration
- Lean condition (insufficient accel enrichment)
- Ignition timing too retarded
- Fuel pressure dropping
- Restricted fuel filter

### Surging at Cruise
- EGO correction oscillating
- VE table cells uneven
- MAP signal noisy
- O2 sensor slow response

### Rich at Light Load
- VE table too high
- Fuel pressure too high
- Leaking injector
- Incorrect required fuel setting

### Lean at WOT
- VE table too low
- Fuel pump insufficient
- Injectors at max duty cycle
- Fuel pressure dropping under load

### Detonation/Knock
- Timing too advanced
- Fuel octane insufficient
- Lean mixture
- Hot intake air (IAT high)
- Carbon buildup
- Incorrect spark plugs

## Safety and Monitoring

### Critical Limits
| Parameter | Warning | Danger |
|-----------|---------|--------|
| Coolant Temp | 100°C | 110°C+ |
| AFR at WOT | 12.0-13.0 | <11.5 or >14.0 |
| EGT | 800°C | 900°C+ |
| Injector DC | 80% | 90%+ |
| Knock | Any | Persistent |

### Data Logging Strategy
**Always log:**
- RPM, MAP, TPS
- AFR (wideband)
- CLT, IAT
- Spark advance
- Injector PW
- Battery voltage

**Add for specific issues:**
- EGO correction (tuning)
- Knock retard (detonation)
- Boost pressure (turbo)
- Oil pressure (engine health)

### Tune Versioning
Save tune with descriptive names:
- `baseline_2024-01-15.msq`
- `idle_tuned_2024-01-20.msq`
- `cruise_complete_2024-02-01.msq`
- `final_v1_2024-02-10.msq`

Include notes about changes in each version.

## Advanced Topics

### Flex Fuel (Ethanol)
- Requires ethanol content sensor
- Blends fuel/spark tables based on ethanol %
- E85 requires ~30% more fuel
- Can retard timing for E85 (slower burn)

### Sequential Injection
- Requires cam position sensor
- More precise fuel delivery
- Better idle and emissions
- Fuel trim per cylinder possible

### Individual Cylinder Tuning
- Requires EGT per cylinder or wideband per runner
- Trim fuel/spark for cylinder variations
- Useful for unequal runner lengths

### Traction Control
- Based on RPM rise rate
- Cuts fuel/spark when wheelspin detected
- Adjustable sensitivity

### Variable Cam Timing
- Control intake/exhaust cam position
- Separate tables for cam advance
- Tuning for low-end torque vs high RPM power