EFII System32

ATA Chapter 73 — N720AK Systems Reference

Overview

The EFII System32 provides complete electronic engine management for N720AK — both fuel injection and ignition. This is a fundamentally different architecture from traditional magneto/mechanical fuel injection systems. The System32 replaces the mechanical fuel servo, magnetos, and mixture cable with ECU-controlled port fuel injection and electronic ignition.

Components

How It Works

Electronic Fuel Injection

The System32 ECU controls fuel delivery through port fuel injectors. It uses sensor inputs (MAP, RPM, temperatures, O2) to calculate injector pulse width. The mixture is automatically optimized — no mixture lever or manual leaning required.

The fuel system is a pressurized loop with MAP-referenced regulation. See Fuel System for complete fuel plumbing and regulator details.

Electronic Ignition

Dual redundant ignition with individual coil packs for each cylinder. The System32 provides:

• Variable ignition timing based on RPM, MAP, and temperature
• Redundant ECU operation — either ECU can run the engine independently
• Panel switch for manual ECU selection

Panel Controls

EFII System32 Switches:

• Ignition Select
• ECU Select
• Fuel Pump Mode (PMP 2)
• Start Battery Select

EFII Breakers (VPX channels):

Annunciator Lamps:

Fuel Compatibility

The EFII System32 supports 100LL and automotive gasoline, with or without ethanol; the closed-loop mapping handles both. Because the rail runs at 45 PSI with continuous return, vapor lock downstream of the pumps is physically impossible — gasoline vapor pressure cannot approach 45 PSI gauge at any survivable temperature. The residual vapor-lock mechanisms are:

• The suction segment (tank pickup → duplex valve → FF-2 pre-filter → pump inlets) carries all the standard mogas physics — this is what the volatility and heat-soak limits in §2 Limitations protect.
• Return-fuel heating: hot rail fuel returns continuously to the selected tank; in a low tank during extended hot ground operations the heat accumulates (the reason EFII’s own manual requires ≥5-gallon header tanks in that architecture). On mogas, avoid long ground ops feeding from a low tank, and switch tanks to spread returned heat.
• The 22 PSI auto-cutover does not protect against suction-side vapor — Pump 2 shares the same inlet plumbing and cavitates on the same vapor. Fuel-pressure fluctuation on mogas means: switch tanks (cooler fuel), reduce power, descend — not “the backup pump will save it.” Cavitation also erodes pump life even when the engine keeps running.

The former 8,000 ft density-altitude and 100 °F OAT limits traced to a single forum post and had no support in EFII, Lycoming, or auto-fuel-STC sources; they were replaced 2026-08-24 with the volatility/temperature limits in §2. Authoritative basis: Lycoming SI 1070AB (IO-540-D approved for ASTM D4814 93 AKI, Vapor Pressure Class A-4, ≤1% oxygenate, LW-16702 additive required) and the Petersen auto-fuel STC certification basis (12,500 ft demonstrated on 110 °F winter-blend fuel in suction-fed aircraft).

Tuning

Wiring

Diagnostics

Inspection & Maintenance

Inspection intervals (SDS-derived)

flyEFII publishes no consolidated inspection schedule. The intervals below are adapted from the SDS EFI Aviation Maintenance/Inspection Schedule (May 2024) — a competing aircraft port-injection system with analogous hardware (brushed fuel pumps, port injectors in the primer bosses, coil packs, Hall crank sensor) — tightened where later SDS service bulletins tightened them. Tracked in recurring-items.tsv.

New installations: check both fuel filters at 10 hr, again at 50 hr, then per the schedule.

Injector cleaning

Neither flyEFII nor SDS publishes a routine injector-cleaning interval. The post-pump fine filter exists to keep particulates out of the injectors, so the filter schedule protects them indirectly. Clean on condition — the symptom is an unexplained single-cylinder EGT shift or a fuel-trim drift — by pulling the PMIs and having them ultrasonically cleaned and flow-matched at an automotive injector service.

SDS service bulletins worth borrowing (different vendor, same physics)

• Starter contactor flyback diodes (SB 2025-06-16): missing diodes on starter solenoids/contactors cause random spark events during cranking and on starter release — kickbacks and backfires, i.e. the ignition source for an induction fire.
• GAMI G100UL not approved (SB 2024-12-27): swelling O-rings, fuel leaks, paint damage; SDS pump/seal components untested with G100UL — EFII components are equally untested. Do not fuel N720AK with G100UL.
• VP-X electronic breakers + EFI (SB 2015-01-15): electronic breakers trip on millisecond coil/injector current peaks far below nominal draw — potential in-flight engine stoppage. N720AK’s architecture already sidesteps this: ignition, injection, and pumps live on the endurance bus behind physical breakers, not the VPX.
• Thread sealant (SB 2015-10-20): never RTV on fuel fittings; Permatex high-performance thread sealant, sparingly, male threads only.
• Lithium batteries (SB 2018-02-08): with lithium batteries (EarthX ETX900 ×2 here), SDS recommends aural high/low-voltage warning plus over-voltage (crowbar) protection.

Project — a custom LOP controller

Status: intended, not started. The doctrine behind it is already settled — Sam worked it out on 2026-08-30 from the PilotWorkshops Airplane Engines manual (red box, pp. 48-53) and the SDS Lycoming Tuning Guide V30. This section records the resulting design target, not an open question.

The goal is a custom controller for the System32 that implements SDS-style lean-of-peak control.

Why SDS is the reference: Racetech’s SDS is a different vendor from flyEFII, but it is the same architecture — fuel and ignition maps indexed by RPM and MAP, with temperature and O2 corrections. Its Lycoming Tuning Guide documents an explicit LOP feature set that the System32 does not expose, and that is the behaviour worth reproducing:

The physics worth carrying over: a fixed-timing magneto cannot advance for a lean mixture, which is a large part of why magneto engines run LOP badly and electronically-managed ones run it well. Any controller built here should treat timing and mixture as one coupled control, not two independent knobs.

The MAP guard is the headline requirement. Today its place is taken by a procedural rule — knob to zero before any power increase — which is a checklist item doing a machine’s job. Automating that single interlock is most of the safety value of the whole project, and it is also worth raising with Robert Paisley as a System32 feature request independent of any custom controller.

Distribution comes before features. LOP is only as good as the worst-distributed cylinder, and the target for clean LOP is a GAMI spread under 0.5 gph. As of the 2026-08-31 trip sweeps the spread ran 1.06-1.47 gph, with cylinder 2 leaking and cylinder 5’s fresh seal drifting lean in flight; the identified fix is to deburr and reseal all six PMI bosses, after which trims should need only ±2-3 %. ECU trims are add-only, 0-9 %, and apply to cylinder POSITION rather than to the injector — so they must be zeroed before any diagnostic swap. Full history and flight-data analysis live in the project memory, not here.

Constraints to design against:

• The System32 runs dual redundant ECUs, either able to run the engine alone. Anything added must not become a single point of failure between the ECUs and the engine, and a map change has to be uploaded to BOTH.
• Live tuning on the System32 adjusts one fuel number per RPM row at squared points; the MAP-axis shape within a row is fixed. A full 2D map can, however, be uploaded on the ground — which is the lever a custom controller would use.
• Leave the ignition map alone as a baseline: EFII’s 30° cruise timing already approximates SDS’s low-MAP-advance strategy.

Reference documents are filed in GDrive Public/Manuals/73-EFII/SDS-reference/ and listed under References below. N720AK does not run SDS — principles transfer, programming does not, and no SDS behaviour should be assumed of the System32 without checking flyEFII’s own documentation.

References

• EFII System32 Installation Manual (Rev 9-13)
• EFII System32 Operating Procedures (12-20)
• EFII System32 Fuel Flow & RPM Config (Rev 10-19)
• EFII System32 Initial Tuning — CSP (Rev 6-20)
• EFII Bus Manager Installation Instructions
• Fuel System — Regulator Diagnostics — fuel pressure analysis
• PLX DM-6 Multi Gauge User Guide
• PLX SM-AFR Gen2 User Guide
• PLX SM-AFR Gen4 Sensor Health Diagnostics — O2 sensor health: replace if <50%. Reaction time: <150ms excellent, >251ms poor. Requires DM-6 V2.0+.
• EFII Port Mount Injector (PMI) Installation
• EFII Throttle Body Flange Adapter (TBFA-1)
• EFII Dual Fuel Pump Module (FPM-1) — Dual Walbro GSL393, 400HP each, 5A/pump, AN-6 fittings. 10A breaker per pump or 20A shared.
• SDS Lycoming Tuning Guide v30 rev4 — the LOP-controller reference. Air/fuel ratio, detonation, ignition mapping, MAP/RPM fuel values, LOP Control / LOP Ignition Advance / LOP Lean Fuel Percent.
• SDS EM-6 Aviation Manual v14.9
• SDS CPI Aircraft Supplement — Lycoming v15
• SDS Maintenance & Inspection Schedule
• SDS Component Current Draws
• SDS tech articles (web): Ignition and Combustion, Start and Warmup Programming, Lycoming 6-cylinder, aviation index