Installation Mistakes That Kill Performance
Ground Loop Issues: The #1 cause of random misfires and sensor errors. Your Holley EFI system needs a dedicated ground path directly to the battery negative terminal. Never share grounds with ignition systems, fuel pumps, or cooling fans.
Power Supply Problems: EFI systems are sensitive to voltage fluctuations. Install a dedicated 12V feed with proper fusing (20A minimum) and use 12-gauge wire or larger. Voltage drop under load will cause erratic behavior.
Sensor Placement Errors: Oxygen sensors must be at least 18 inches downstream from the header collector. MAP sensors need vacuum reference from the intake manifold, not individual runners.
EMI/RFI Interference Solutions
Ignition System Interference: MSD and other capacitive discharge ignitions can interfere with EFI operation. Route ignition wires away from ECU harnesses and use shielded spark plug wires.
Alternator Noise: High-output alternators generate electrical noise that confuses sensors. Install a noise suppressor on the alternator output and ensure proper grounding.
Fuel Pump EMI: Electric fuel pumps create electromagnetic interference. Use a relay to power the pump and install a noise filter on the power feed.
Critical Sensor Diagnostics
TPS (Throttle Position Sensor): Should read 0.5V at idle, 4.5V at WOT. Erratic readings indicate a failing sensor or poor connection.
IAT (Intake Air Temperature): Resistance should match air temperature. At 70°F, expect 2.3-2.7k ohms. Values outside this range require sensor replacement.
Coolant Temperature Sensor: Critical for cold-start enrichment. Should read 2.3k ohms at 70°F, dropping to 300 ohms at 200°F operating temperature.
MAP Sensor Calibration: At sea level with engine off, should read 29.92 inHg (14.7 PSI). Low readings indicate vacuum leaks or sensor failure.
Fuel System Requirements
Fuel Pressure Consistency: EFI systems require steady fuel pressure. Install a fuel pressure gauge and monitor under all operating conditions. Pressure should remain within ±2 PSI of target.
Fuel Quality Issues: Ethanol fuels can cause lean conditions if not properly compensated. Ensure your tune accounts for fuel type and quality variations.
Injector Flow Matching: Mismatched injectors cause cylinder-to-cylinder variations. Flow test all injectors and replace any that vary more than 5% from the average.
Tuning Solutions for Common Problems
Cold Start Issues: Increase cranking pulse width and adjust cold enrichment tables. Most Holley systems need 15-25ms cranking pulse for reliable starts below 40°F.
Hot Start Problems: Reduce cranking pulse width for hot conditions and verify coolant temperature sensor accuracy. Heat soak can cause false readings.
Idle Stability: Set idle speed 50-100 RPM higher than desired final idle. Use IAC (Idle Air Control) to bring RPM down to target. This provides better control authority.
Part-Throttle Tuning: Focus on the 15-60 kPa range where most driving occurs. Smooth transitions are more important than peak power in this range.
Advanced Diagnostic Procedures
Data Logging Analysis: Log TPS, MAP, RPM, and AFR simultaneously during problem conditions. Look for correlations between inputs and symptoms.
Voltage Testing Under Load: Many problems only appear under electrical load. Test all sensor voltages with headlights, electric fans, and fuel pump running.
Mechanical Inspection: EFI won't fix mechanical problems. Verify compression, cam timing, and vacuum leaks before blaming the EFI system.