Haitian Heavy Diesel Vehicle Shows One-Cylinder Weakness Only Under High Load Despite Near-Normal Leak-Off as Injector Inlet Microfilter and Fuel Passage Restriction Are Investigated

The Cylinder Looked Acceptable at Light Load

In a representative heavy-diesel vehicle case in Haiti, one cylinder showed acceptable behavior during light operation but contributed less when engine load increased.

Injector leak-off testing did not reveal a large return-flow difference.

This shifted the investigation toward another possibility: could fuel entering that injector be locally restricted?

Internal Leakage and Inlet Restriction Produce Different Patterns

Excessive leak-off means fuel entering the injector is escaping internally in abnormal quantity.

An inlet restriction means the injector may not receive enough fuel in the first place.

These mechanisms can create different test results.

At lower demand, a partially restricted passage may still supply enough fuel.

At higher demand, the restriction can become more significant.

The Injector Inlet Became a New Checkpoint

Some injector designs incorporate a fine inlet screening or edge-filter feature intended to manage contamination entering precision internal passages.

Where this structure exists, technicians can consider whether:

• debris is present;
• the inlet is restricted;
• contamination has reached the injector;
• or upstream fuel cleanliness is inadequate.

This should only be assessed using an appropriate injector-repair procedure.

Why Normal Leak-Off Did Not End the Diagnosis

Near-normal return flow indicated that the injector did not obviously have excessive internal leakage under the tested condition.

It did not prove that the injector could receive and deliver the required fuel quantity under higher demand.

The workshop therefore separated:

What comes into the injector
from
What returns from the injector

Upstream Contamination Had to Be Investigated

If debris is found at an injector inlet, simply cleaning or replacing one injector may not solve the cause.

The workshop should also review:

• fuel filter condition;
• fuel lines;
• high-pressure system cleanliness;
• previous pump damage;
• and recent repair history.

A restricted inlet can be evidence of a larger contamination pathway.

Full Testing Followed Inspection

After the inlet condition was addressed, the injector required controlled testing for:

• delivery;
• return;
• response;
• and consistency across applicable operating points.

Case Insight

The Haitian case used a fuel-entry diagnostic model:

Light load acceptable → High-load cylinder weakness → Leak-off near normal → Injector inlet checked → Upstream contamination considered → Delivery retested

This avoided treating return flow as the only meaningful injector measurement.

FAQ

Can an injector have normal leak-off but still deliver too little fuel?

Potentially, because inlet restriction or another delivery-side issue may exist without excessive internal return.

Do all injectors contain the same inlet microfilter design?

No. Internal inlet structures vary by injector type.