The 128-6601 is a fuel injector part number manufactured by Caterpillar for use in several of their mid-to-large-sized diesel engines. It is a Hydraulically-Actuated, Electronically-Controlled Unit Injector (HEUI).

This means it uses high-pressure engine oil (hydraulic pressure) to create the immense fuel pressure needed for injection, while an electronic solenoid valve, controlled by the engine's ECM (Electronic Control Module), precisely controls the timing and duration of the fuel spray.

Common Applications

The 128-6601 injector is used in several popular and widely-used Caterpillar engine families. The most common applications include:

• Caterpillar C7 Engine: Found in a variety of trucks and industrial equipment.

• Caterpillar C9 Engine: Used in trucks, construction equipment, and industrial power units.

• Caterpillar C11 Engine: A common engine in heavy-duty trucks and vocational vehicles.

Specific Equipment Examples:

• Trucks: International 9000 series, Kenworth T800, Peterbilt 379/387 with CAT engines.

• Construction Equipment: Various models of Caterpillar loaders, bulldozers, and excavators.

• Industrial: Generator sets, pumps, and other stationary power applications.

Crucial Note: Always verify the correct part number for your specific engine serial number using the Caterpillar parts system or by consulting with a certified technician. Using the wrong injector can cause severe engine damage.

Key Features & Technology

1. HEUI System: Unlike traditional injectors that rely solely on camshaft force, the HEUI system uses engine oil pressure (amplified by a high-pressure oil pump) to actuate the injector. This allows for very high injection pressures independent of engine RPM.

2. Electronic Control: The Engine Control Module (ECM) sends a signal to the injector's solenoid, providing precise control over injection timing and fuel quantity. This leads to better fuel efficiency, lower emissions, and more power.

3. High Pressure Capability: HEUI injectors can generate injection pressures exceeding 30,000 PSI, which results in excellent fuel atomization for a cleaner and more complete burn.

Common Symptoms of a Failing 128-6601 Injector

If one or more of these injectors are failing, you may experience:

• Hard Starting or No Start: Difficulty starting the engine, especially when cold.

• Rough Idle or Misfire: The engine shakes, stumbles, or runs unevenly at idle.

• Loss of Power: Noticeable lack of power under load.

• Excessive White or Black Smoke: Unburned fuel (white smoke) or a overly rich mixture (black smoke) exiting the exhaust.

• High Fuel Consumption: A sudden drop in fuel mileage.

• Engine Knocking or "Dead Hole": A loud knocking sound from one cylinder, indicating a misfire.

• Oil in Fuel or Fuel in Oil: Due to the internal seals failing, engine oil can leak into the fuel system, or fuel can dilute the engine oil. This is a critical failure mode for HEUI injectors.

• Diagnostic Trouble Codes (DTCs): The ECM will often store codes related to cylinder misfires (e.g., CID FMI codes) or injector circuit faults.

Important Considerations for Replacement & Repair

1. Buy Quality: This is a critical component. Opt for Genuine Caterpillar® Remanufactured injectors whenever possible. They are rebuilt to exact factory specifications, come with a warranty, and include a new set of copper seals. Avoid cheap, uncertified aftermarket injectors.

2. Replace in Sets: While it's possible to replace just one faulty injector, it is often recommended to replace them as a matched set (especially on the same bank). When one injector fails, others are often not far behind, and labor costs to access them are high.

3. Professional Installation is Key: Replacing HEUI injectors is not a simple "plug-and-play" job. It requires:

• Cleaning: The injector bore must be meticulously cleaned before installation.

• New Seals: New O-rings and copper seals must be used.

• Coding: After installation, the new injector's trim code (a calibration number unique to each injector) must be programmed into the ECM using Caterpillar electronic software (ET or CAT® ET). If this is not done, the engine will not run correctly.

• High-Pressure Oil System Check: The health of the high-pressure oil pump, lines, and rails should be verified.

4. Address the Root Cause: A failing injector can sometimes be a symptom of another problem, such as contaminated fuel, a failing high-pressure oil pump, or a weak ECM driver. A good technician will diagnose the entire system.

   
   

   The Caterpillar 128-6601 HEUI fuel injector has several distinct advantages and features that stem from its innovative design, which differs significantly from traditional mechanical or common-rail injectors.

   Here’s a breakdown of its key advantages and features:

   Key Features (The "What it Is")

   HEUI Technology (Hydraulically-Actuated, Electronically-Controlled Unit Injector):

   Dual-Fluid System: This is the core feature. It uses engine oil (hydraulic fluid) for actuation pressure and diesel fuel for injection.

   Electronically Controlled Solenoid: A solenoid valve, controlled by the engine's ECM (Electronic Control Module), opens and closes to precisely start and stop fuel injection.

   Pressure Multiplication: The injector contains an intensifier piston. High-pressure engine oil acts on the large area of this piston, which in turn acts on a smaller-area piston pressurizing the fuel. This mechanically multiplies the oil pressure, creating extremely high fuel injection pressures (often over 30,000 psi / 2,000 bar) without the need for a camshaft or a ultra-high-pressure fuel pump.

   Integrated Unit Injector Design: It combines the injection pump and injector nozzle into a single unit that sits directly in the cylinder head. This eliminates high-pressure fuel lines, reducing potential leak points and pressure losses.

   Advantages (The "Why it Matters")

   The features above translate into direct benefits for engine performance, efficiency, and control.

   High Injection Pressure Independent of Engine Speed:

   Cleaner Combustion: Less soot and particulate matter.

   Better Cold Starts: Excellent atomization even when cranking.

   More Power and Torque: Efficient burning at low RPMs.

   Feature: Uses pressurized engine oil from a separate pump, not the camshaft.

   Advantage: Unlike traditional systems where injection pressure drops at low RPM, the HEUI system can maintain optimal, high injection pressure at any engine speed. This results in superior fuel atomization across the entire operating range, leading to:

   Unmatched Injection Control and Flexibility:

   Pilot Injection: A tiny amount of fuel is injected before the main injection event to soften combustion, drastically reducing noise (knock) and NOx emissions.

   Rate Shaping: Controlling the shape of the injection rate for a smoother and more efficient burn.

   Multiple Injection Events: Precisely timed bursts of fuel for optimal power and minimum emissions.

   Feature: Full electronic control via the ECM.

   Advantage: The ECM can manage injection timing and duration with extreme precision. This allows for advanced strategies like:

   Excellent Reliability and Packaging:

   Eliminates Line Failures: No risk of catastrophic high-pressure fuel line ruptures.

   Compact Design: Simplifies the engine design by integrating functions into one component.

   Consistent Performance: With fewer external components, performance is more consistent and reliable.

   Feature: Unit injector design with no high-pressure lines.

   
   

Technical Parameters: Caterpillar 128-6601 Fuel Injector