2.11 Diesel Runaway Protection¶

Overview¶

Layered, fully mechanical defense against diesel runaway on the Cummins R2.8. The strategy has two independent layers:

1. Prevention - Mishimoto baffled catch can in the crankcase ventilation path blocks the most common runaway initiator (oil ingestion via PCV).
2. Termination - AMOT 4261M intake air shutoff valve in the pre-turbo intake tract, manually actuated by a dash-mounted push-pull cable with locking T-handle.

This is a deliberate departure from Cummins' Repower default (no air shutoff) because the ECM kill path documented in Keyless Ignition (normal shutdown drops the PBS-I PINK IGN output, cutting ECM power — the PMU is not in this path) cannot stop a runaway that is sustained by oil or hydrocarbon vapor — the ECM can be cutting injector commands and the engine will still run. The AMOT cable is the only kill path that works under all failure modes, including total electrical/ECM failure.

Components¶

Catch Can: Crankcase Ventilation¶

Plumbing¶

R2.8 valve cover breather
    ↓
5/8" oil-resistant hose (engine-side)
    ↓
Catch can INLET (top)
    │  Baffled separation
    ▼
Catch can OUTLET (top)
    ↓
5/8" hose to turbo inlet
    ↓
Turbo inlet (pre-compressor)

Mounting¶

• Engine bay, intake side, away from exhaust manifold heat
• Vertical orientation; petcock at bottom for draining
• Within easy reach for visual inspection at every oil change

Function¶

The R2.8 routes crankcase blow-by vapor back to the pre-turbo intake (factory closed PCV). The baffled can sits in this line. Oil mist condenses on the internal baffles and collects in the reservoir; clean vapor continues to the intake. This blocks the most common runaway initiator on small modern diesels: oil carryover from a worn turbo shaft seal or overfilled crankcase being burned as supplemental fuel.

AMOT 4261M: Manual Air Shutoff¶

Valve Specifications¶

Intake Connection¶

The 4261M is a wafer butterfly valve with no threaded air-path port — it sleeves into the 2.8" (71 mm) nominal intake duct and is secured with hose clamps. The R2.8 turbo inlet tube measures 2.125" OD / 1.63" ID.¹ That is well below both the valve's 2.8" connection and its 2.4" bore, so the valve adds no flow restriction, but the turbo side needs reducer couplers stepping 2.8" → 2⅛". The NPT thread in part number 4261M02A027-AA (actuator code 27) is the pneumatic control port, not the air path; this build trips the valve by manual cable, leaving that port unused. Exact reducer sizing pending confirmation of the valve's air-path connection OD — see #129.

Cable + Handle Specifications¶

Mounting¶

• Valve location: Pre-turbo intake tract, between air filter outlet and turbo inlet. Must be pre-turbo — post-turbo placement does not work because the line is pressurized during normal operation and the turbo itself stores enough air to sustain runaway briefly.
• Handle location: Dash, driver-accessible without leaving belted position. Label: EMERGENCY ENGINE SHUTOFF — PULL TO STOP.
• Cable routing: Through firewall via a dedicated grommet (not shared with other cables), secured every 12" with adel clamps to prevent chafing or sag. Avoid sharp bends (≥6" radius).

Function¶

In normal operation the valve is cocked open and held by an internal latch. The cable handle sits flush against the dash bezel. When the driver pulls the T-handle:

1. Cable pulls the AMOT trip lever ≥15 lb of force
2. Internal latch releases
3. Return spring snaps butterfly closed within ~100 ms
4. Engine starves of intake air and stops within 1–2 seconds

The handle's turn-to-lock feature prevents accidental actuation (turn quarter-turn to unlock before pulling) and holds the cable in the tripped position after pulling (turn to lock-pulled).

Reset Procedure¶

The 4261M does not auto-reset. After actuation:

1. Determine and resolve the cause (oil ingestion, fuel leak, etc.)
2. Open the hood
3. Manually re-cock the AMOT butterfly using the lever on the valve body
4. Push the dash T-handle back to flush, turn to lock-closed
5. Restart engine via normal keyless sequence

This is intentional — it forces a diagnosis step and prevents an unattended restart into the same fault.

Failure Modes Covered¶

The last row is the conscious limitation of the manual-only design. Adding speed-sensed auto-trip would require AMOT 4261M with electric solenoid actuator (4261M02A071-AA) plus an 8210K speed switch — see Future Enhancements.

Maintenance¶

Standards Context¶

The off-road LJ build sits between consumer and industrial use cases. Fuel handling during recovery, dust/oil exposure, and modified intake plumbing all push the risk profile toward the industrial side, justifying the additional protection.

Future Enhancements¶

Two upgrade paths from this baseline, neither required:

1. Add electric solenoid auto-trip — replace AMOT actuator option 27 with option 71 (electric solenoid, 12 VDC) and feed it from a speed switch driven by the alternator W terminal or a magnetic crank pickup. Auto-closes on overspeed condition.
2. Add overspeed sensing — AMOT 8210K electronic speed switch + magnetic pickup wired to drive the solenoid above. Provides automatic protection independent of driver action.

Both upgrades preserve the manual cable as the always-available backup.

Outstanding Items¶

Build Tasks¶

• Measure R2.8 turbo inlet tube: 2.125" OD / 1.63" ID (resolves #54). 2.8" AMOT is the smallest 4261M (2.4" bore) — oversized but adds no restriction; reducer couplers required.
• Confirm AMOT 4261M 2.8" air-path connection OD and select reducer coupler to 2.125" intake tube (#129)
• Select dash T-handle mounting location (within reach belted, away from accidental contact)
• Assign firewall grommet for AMOT cable pass-through (dedicated grommet required)
• Determine catch can mounting bracket attachment point on engine bracketry

Related Documentation¶

• Keyless Ignition - Why ECM-only kill is insufficient; this doc supersedes the prior "no protection" note
• Engine Systems Checklist - Phase 11 install steps
• TBD Tracker - Open items for parts selection
• Purchase Tracker - BOM line items