Newmar King Aire fire

[newmarokie]

I THINK all Cummins engines use VGT technology now. It increases the RPM range in which the turbo can increase performance and helps on fuel economy in normal driving conditions. I will speak with my shop manager and see if he can recall if any of our trucks don't have VGT turbos for some idea.

 

[Joe Dutchstar]

Grok Says:

Cummins diesel engines equipped with Variable Geometry Turbochargers (VGTs) include several models across different applications, primarily utilizing Holset VGT technology. Below is a list of notable Cummins engines known to use VGTs, based on available information:

• 6.7L Cummins (Inline-6):
  • Used in Ram 2500/3500 trucks (2007.5–present). The Holset HE351VE or HE300VG VGT provides improved low-end torque and efficiency, with models from 2013 onward featuring refined VGTs for better performance and emissions control.65
  • Common in heavy-duty pickup applications, delivering up to 400 hp and 1,000 lb-ft of torque in high-output versions.
• ISB 6.7L:
  • Found in medium-duty trucks, buses, and industrial applications. This engine often uses a Holset VGT (e.g., HE351VE) to optimize performance across a wide RPM range, particularly for on-highway use.18
• ISL 8.9L:
  • Employed in heavy-duty trucks, buses, and some off-highway equipment. The ISL often incorporates a Holset VGT for better fuel economy and emissions compliance, especially in applications requiring consistent power delivery.3
• ISX 15.0L (now X15):
  • Used in heavy-duty on-highway trucks (e.g., commercial freight). The ISX/X15 series has utilized Holset VGTs, such as the HE551V or HE500VG, to enhance transient response and meet stringent emissions standards like EPA 2010 and beyond.01
• QSB, QSL, and QSX Series:
  • These engines, used in industrial, marine, and power generation applications, may feature VGTs depending on the configuration. For example, certain QSB 6.7L and QSL 9L models in off-highway equipment use Holset VGTs to optimize performance for variable load conditions.3

Notes:

• Not All Models: While VGTs are common in modern Cummins engines for on-highway and some off-highway applications, older models or specific configurations (e.g., light-duty or certain industrial applications) may use fixed geometry or wastegate turbochargers instead.58
• Holset VGT Technology: Cummins’ Holset brand is the primary supplier of VGTs, with models like the HE300VG, HE351VE, and HE561VE tailored to specific engine needs. These turbochargers adjust vane geometry to optimize boost, reducing lag and improving efficiency.01
• Application-Specific: The use of VGTs depends on the engine’s intended use (e.g., on-highway trucks, off-highway equipment, or marine). For precise details on a specific engine model or year, checking with Cummins technical documentation or a dealer.

 

[turbopilot]

From Grok how they work:

Understanding Engine BrakingEngine braking, also known as compression braking, occurs when a vehicle's engine slows the drivetrain by resisting the pistons' movement during deceleration. This happens primarily in the intake stroke, where the closed throttle creates a vacuum, forcing the pistons to compress air without fuel ignition. In diesel engines, which lack a traditional throttle plate, engine braking relies more on exhaust backpressure to amplify this effect. A variable geometry turbocharger (VGT) plays a key role here by dynamically controlling exhaust flow to generate this backpressure.What is a Variable Geometry Turbocharger (VGT)?A VGT is an advanced turbocharger design that uses adjustable vanes or nozzles in the turbine housing to optimize exhaust gas flow across a wide range of engine speeds. Unlike fixed-geometry turbos, which can suffer from turbo lag at low RPMs or inefficiency at high RPMs, VGTs adapt by pivoting vanes (or sliding rings/walls) to widen passages for high-flow conditions or narrow them for low-flow scenarios. This is typically controlled by an electronic actuator responding to engine load and speed.How VGT Enables Engine BrakingVGTs enhance engine braking by functioning as an integrated exhaust brake, creating significant backpressure in the exhaust system without needing separate hardware like a throttle valve. Here's the step-by-step mechanism:

1. Activation During Deceleration: When the driver lifts off the accelerator (e.g., on a downhill), the engine control unit (ECU) signals the VGT actuator to adjust the vanes. The vanes pivot or slide to a closed position, narrowing the exhaust passages around the turbine wheel.
2. Exhaust Flow Restriction: This adjustment restricts the flow of exhaust gases leaving the cylinders, building high pressure (backpressure) in the exhaust manifold—often exceeding the intake manifold pressure. The turbine spins slower due to the reduced gas velocity, but the restricted path traps more exhaust gas in the cylinders.
3. Amplified Compression Resistance: During the exhaust stroke, the pistons must push against this elevated backpressure to expel gases, requiring more work from the engine's inertia (transferred from the wheels). This resistance slows the vehicle more effectively than standard compression braking. In diesels, it can also induce some exhaust gas recirculation (EGR) by reversing flow direction momentarily, further aiding control.
4. Sustained Effect: The ECU maintains this vane position as long as braking is needed, modulating it based on speed and load to avoid over-stressing components like the turbo bearings.

This process is particularly effective in heavy-duty diesel applications, like trucks, where VGTs (e.g., Holset models on Cummins engines) can generate braking forces equivalent to 200-300% of normal engine braking.Benefits of VGT for Engine Braking

• Enhanced Performance: Provides stronger, more consistent braking torque, especially at low engine speeds, improving vehicle control on grades.
• Simplified Design: Eliminates the need for an additional exhaust brake valve, reducing weight, cost, and complexity.
• Emissions and Efficiency Gains: Raises exhaust temperatures to support diesel particulate filter (DPF) regeneration and meets strict emissions standards (e.g., Euro 5/6 or EPA 10) by controlling NOx during transients. However, excessive backpressure must be managed to avoid fuel economy penalties.
• Broader Engine Optimization: While braking, it maintains better air-fuel ratios, reducing smoke and wear.

In summary, VGTs transform a turbo from a boost provider into a braking tool by leveraging adjustable geometry for precise exhaust control, making them a staple in modern diesel engines for safety and efficiency.

 

[turbopilot]

And from Grok these are the failure modes. My F550 VGT failed by 3rd mode listened here.

Typical Failure Modes for Variable Geometry Turbochargers (VGTs) During Engine BrakingVariable geometry turbochargers (VGTs) enhance engine braking by closing vanes to create exhaust backpressure, but this process introduces high mechanical and thermal stresses on the system. While regular use of the exhaust brake function can actually help prevent some buildup issues by promoting self-cleaning through high exhaust flow, excessive or improper use—combined with inherent design vulnerabilities—can lead to failures. Below are the most common failure modes, drawn from diesel engine diagnostics (primarily in heavy-duty applications like Cummins 6.7L), including causes, symptoms, and mitigation strategies.1. Actuator Failure (Most Common)

• Description: The electronic or pneumatic actuator that controls vane position fails, often sticking in a closed (braking) or open position. This is exacerbated during engine braking because the actuator must repeatedly cycle under high backpressure and heat.
• Causes: Wear from frequent cycling, weakening magnets/electronics in the armature, insufficient torque, or soot/carbon contamination affecting motion. Overuse of the exhaust brake may accelerate wear, though it's not the sole factor.
• Symptoms: Loss of braking power, reduced boost under acceleration (e.g., stuck vanes at 94% closed causing high backpressure), check engine lights (e.g., P2262 or U010C codes), excessive smoke, or erratic vane positioning (e.g., stuck at 4.7 on a 0-7 scale).
• Mitigation: Regular calibration post-replacement using tools like Alfa OBD software; clean or replace the actuator ($800–$900 USD); avoid excessive braking in cold conditions. In some cases, full turbo replacement under warranty.

2. Stuck or Binding Vanes/Unison Ring

• Description: The adjustable vanes or the unison ring (which synchronizes vane movement) seize up, preventing proper closure for braking.
• Causes: Accumulation of soot, carbon, rust, or grime on the exhaust-side components, worsened by short trips or idling. During braking, the closed position traps hot exhaust gases, potentially baking on deposits if not cleared regularly—though braking itself can help dislodge buildup.
• Symptoms: No engine braking effect, poor low-RPM response, excessive exhaust smoke, or over-boost/high EGTs. May trigger P0299 (underboost) codes.
• Mitigation: Use the exhaust brake periodically to self-clean via high-velocity flow; clean the turbine housing or replace the ring/vanes. Switching to a fixed-geometry turbo eliminates this issue entirely.

3. Bearing Failure in the Center Section

• Description: Thrust or journal bearings wear out prematurely, leading to shaft play and potential compressor/turbine wheel damage.
• Causes: Elevated drive pressures and shaft speeds during braking (VGTs generate 20–50% more backpressure than fixed turbos), compounded by aftermarket tuning or poor oil quality. High loads from vane closure stress the turbine bearings directly.
• Symptoms: Whining noises, excessive oil consumption, compressor wheel rubbing (inducer contact), or sudden loss of boost/braking.
• Mitigation: Use high-quality synthetic oil and follow change intervals; limit aggressive braking on modified engines; rebuild or replace the turbo if play exceeds 0.003–0.005 inches.

4. Exhaust Backpressure Sensor or Related Sensor Malfunctions

• Description: Sensors monitoring backpressure fail, disrupting ECU control of the VGT during braking.
• Causes: Soot contamination in the sensor tube or faulty wiring, often highlighted during warm-up or high-load braking when pressures fluctuate.
• Symptoms: Delayed "warm-up" for braking activation, inconsistent backpressure, or false engagement (e.g., braking during acceleration). May include noise from loss of pilot injection.
• Mitigation: Clean the sensor and tube regularly; replace if faulty (inexpensive part); data-log vane positions vs. demands for diagnosis.

General Design Considerations and PreventionVGTs must be engineered for braking loads (e.g., reinforced mechanisms in heavy-duty units), but real-world failures often stem from inadequate maintenance in soot-prone diesel environments. Overall prevention includes:

• Routine Use: Engage the exhaust brake on grades to prevent buildup, but avoid overuse in extreme conditions.
• Maintenance: Follow OEM cleaning schedules (e.g., every 100,000 miles for Cummins actuators); monitor EGTs and codes.
• Upgrades: For high-mileage or tuned engines, consider fixed-geometry alternatives to sidestep VGT complexities.

These modes are most reported in Cummins and Power Stroke applications, where VGTs double as exhaust brakes. If symptoms appear, professional diagnosis via OBD scanning is recommended to avoid cascading damage.