2339635 | Genuine Paccar® Back Pressure Valve For MX13 2018-2025

It holds back the flow of exhaust, air, fuel, or hydraulic fluid to keep the system at a stable, required pressure level.

2. Ensures Proper System Operation

Many systems—especially diesel engines—need a certain amount of pressure to operate components correctly, such as:

• Turbochargers

• Emission systems

• Engine braking systems

• DEF/SCR emission equipment

3. Controls Flow

The valve restricts flow until a set pressure is reached, then opens to release excess pressure.

1. Poor Engine Performance

• Loss of power

• Slow acceleration

• Turbo lag or weak boost
  If the valve sticks closed, it causes excessive exhaust restriction.

2. High Exhaust Temperatures

• Engine or exhaust system overheating

• Possible DPF (Diesel Particulate Filter) regeneration problems
  A stuck valve increases exhaust heat and pressure.

3. Rough Idle or Stalling

• Engine idles unevenly

• Stalls when the valve is stuck partially closed

4. Excessive Smoke From Exhaust

• Black smoke: too much restriction

• White smoke: improper exhaust back pressure during cold operation
  Indicates incorrect combustion due to pressure imbalance.

5. Reduced Fuel Economy

• Engine works harder due to incorrect back pressure

• Wasted fuel and higher consumption

6. Engine Brake Not Working Properly (if system uses back pressure)

• Weak or no engine braking

• Jerky or inconsistent brake operation

7. Check Engine Light or Warning Messages

Common codes relate to:

• Exhaust back pressure sensor faults

• Stuck exhaust valve

• Turbo underboost/overboost

• Regeneration efficiency faults

8. Hissing, Ticking, or Unusual Exhaust Noises

• Valve sticking

• Leaks around exhaust components

• Air escaping through a damaged valve

9. Slow Warm-Up or Hard Cold Starts

If the valve fails open, the engine may take longer to reach operating temperature.