Caterpillar 227-5968 Ignition Module

CATERPILLAR 227-5968 Ignition System Module (Altronic CPU-95 II) for CAT G3406 / 3406 Gas Engines

The Caterpillar 227-5968 Ignition System Module (engineered and manufactured by Altronic under the CPU-95 II / CPU-95 architecture) is a capacitive discharge ignition (CDI) unit. Engineered specifically for stationary gas engines, continuous power generation sets, marine auxiliary installations, and gas compression platforms, this module delivers crankshaft-referenced spark timing accuracy to within fractions of an engine degree.

Operating on a nominal 24 VDC industrial power feed, the 227-5968 replaces older, mechanical magneto-drive assemblies and early-generation electronic modules. By directly sampling flywheel ring-gear teeth (or drilled timing holes) and a camshaft-driven Hall-effect cycle trigger, the CPU-95 II eliminates gear backlash, timing drift, and mechanical wear. The onboard logic calculates instantaneous ignition retard/advance dynamically through remote 4–20 mA current loop interfaces, automated engine speed mapping (RPM vs. timing), and single-step remote contact switches.

Model Details

• Caterpillar Part Number (MPN): 227-5968 / 2275968
• Original Equipment Manufacturer (OEM): Altronic, LLC (Girard, Ohio, USA)
• OEM Base Series: Altronic CPU-95 / CPU-95 II Digital Ignition System
• OEM Cross-Reference / Interchangeable Series: 791950-8, 791950-16, 791958-8, 791958-16 series
• Retrofit Equivalents: Supersedes legacy Altronic III, Altronic III-CPU, and CPU-90 systems

Features

1. True Crankshaft-Referenced Timing Accuracy: Samples 180+ flywheel ring-gear teeth alongside a camshaft Hall-effect index pin, delivering instantaneous, drift-free ignition timing that eliminates mechanical magneto backlash and torsional vibration error.
2. Dynamic Variable Timing Control: Offers full closed-loop automated timing adjustments via 4–20 mA supervisory current loops (load/emissions mapping), RPM-based look-up curves, keypad manual offsets, and external discrete one-step retard contacts.
3. Selectable Spark Energy & Multi-Strike Delivery: Programmable for single-strike or multi-strike discharge modes (up to 1,050 RPM) across three field-selectable primary energy tiers, optimizing cold starts and lean-burn combustion stability.
4. Advanced Cylinder-by-Cylinder Diagnostics: Detects shorted/open primary and secondary ignition leads, tracking relative spark voltage demand per cylinder with dedicated alarm/fault solid-state relay outputs.
5. Hazardous-Location Architecture: Certified for Class I, Division 2, Group D operating environments with an ambient tolerance from -40°C to +70°C (-40°F to +158°F) and an RS-485 Modbus RTU communications backbone.

Technical Specifications

Equipment Compatibility

Supported Engine Models

• Caterpillar G3406 / 3406 SITA / 3406 TA Gas Engines: In-line 6-cylinder spark-ignited natural gas, landfill gas, digester gas, and propane configurations.
• Caterpillar G3300 Series (Reference installations): G3304, G3306 (with appropriate engine configuration memory chip/EEPROM).
• Caterpillar G3408 / G3412 (Variant Specific): Supported via multi-channel Altronic harness routing and matching firing EEPROM configurations.

Compatible Ignition Coils & System Peripherals

• Altronic Coils: 501061, 591010, 591011A, 591012, 591018 series (unshielded and explosion-proof shielded integral coils).
• Caterpillar Ignition Coils: Standard CAT threaded shielded coils and direct-to-plug transformers.
• Display Modules: Altronic CPU-95 Display Module (P/N 791960 series) with 16×2 backlit LCD.
• Pickup Assemblies: Dual magnetic pickup brackets, ferrous flywheel ring-gear sensors, and cam-mounted Hall-effect reference assemblies.

Applications

• Marine Auxiliary Gas Generation: Prime electrical power generator sets on gas-carrier vessels (LNG/LPG), offshore floating production storage and offloading units (FPSO), and marine workboats.
• Gas Compression & Pipeline Pumping: Remote field gas-gathering skids, natural gas gathering booster compressors, and pipeline transmission stations driven by CAT G3406 engines.
• Distributed Power Generation & CHP: Continuous-duty base load cogeneration facilities, peak-shaving containerized gen-sets, and bi-fuel microgrid backup installations.
• Waste Gas & Biogas Recovery: Landfill methane extraction plants, municipal wastewater digesters, and agricultural biogas recovery skids with high levels of H2S requiring precise combustion energy control.

Our Chief Engineer’s Guide:

• Separation of Conduit Runs is Non-Negotiable: The CPU-95 II chassis provides three isolated base conduit entries. Never pull the magnetic pickup cables (Center Entry) through the same conduit or wire tray as the 24 VDC main power supply or primary high-energy coil lines (Right/Left entries). Transient electromagnetic interference (EMI) from coil discharges will couple into the position sensor signals, creating intermittent sync loss, false overspeed triggers, or random misfires.
• Grounding Topography: Ensure the module is grounded directly to the engine block using a dedicated 12 AWG tinned-copper bonding strap. Avoid daisy-chaining ground studs back through remote control panels where earth potentials can float.
• Flywheel Ring-Gear Pickup Air Gap: Mount the primary magnetic speed pickup perpendicular to the gear tooth crown with an air gap set precisely between 0.020″ and 0.035″ (0.50 mm to 0.89 mm). Run the flywheel through a full 360-degree barring rotation while measuring runout with a dial indicator; maximum gear runout relative to the pickup face must not exceed 0.007″ (0.18 mm).
• 4–20 mA Current Loop Calibration: Terminals allocated for timing control (typically Terminals 1 and 2) operate on a linear curve where 4.0 mA corresponds to base (advanced) timing and 20.0 mA applies full retard. If retrofitting a legacy panel, verify that your loop power supply common does not form an accidental ground loop with the 24 VDC engine power negative.
• High-Voltage Coil Leads: Limit secondary HT leads from Altronic coils to spark plugs to a maximum length of 24 inches (600 mm). Maintain at least 2 inches (50 mm) of clearance between spark plug boots/wires and uninsulated grounded metal engine surfaces to prevent spark tracking.

Frequently Asked Questions

What causes a “SYNC ERROR” or “STALLED” code on the Caterpillar 227-5968 display?

A “SYNC” or “STALLED” diagnostic message occurs when the CPU-95 II does not detect matching pulses between the flywheel magnetic pickup (engine position) and the camshaft reset pickup. This is typically caused by an improper sensor air gap, metal shavings accumulating on the magnetic pickup face, damaged pickup wiring shielding, or an unindexed camshaft trigger magnet.

Can the Caterpillar 227-5968 replace mechanical magnetos on older CAT 3406 engines?

Yes. Upgrading from a mechanical magneto to the Altronic CPU-95 II system eliminates drive gears and couplings. The retrofit requires installing a magnetic pickup bracket on the flywheel housing, a Hall-effect sensor on the cam inspection access, the 227-5968 control box, and matching Altronic or Caterpillar shielded primary harnesses.

What is the input DC voltage operating tolerance for this ignition module?

The module is designed for a nominal 24 VDC input. It operates within a voltage range of 20 VDC to 32 VDC. In installations where heavy starter cranking drops line voltage below 18 VDC, a dedicated battery-backed DC power supply or transient-protected ignition supply is required to prevent module reset during engine cranking.

How does the 4–20 mA timing loop control ignition timing?

The module’s analog input reads a 4–20 mA current loop from an external control system (such as an emissions controller, knock-detection system, or PLC). Typically, 4 mA leaves the timing at full programmed advance, while increasing the loop to 20 mA proportionally retards ignition timing (up to the programmed degree limit) to manage detonation and comply with exhaust emissions standards.

Can I run dual coils per cylinder with the 227-5968 module?

Yes. The output circuits support parallel-wired dual-coil per cylinder setups when using approved Altronic high-performance coils. Ensure the 24 VDC power feed can supply up to 10 Amperes continuous load to satisfy high-firing-frequency energy demands.