1. Fuel Delivery (despite the new pump):
* High-pressure fuel system issues: The electric pump addresses low-pressure supply from the tank, but the *injection pump* itself might have internal wear or problems delivering fuel at the correct pressure and timing *under load*. This is a common issue with older diesel injection pumps. A qualified diesel mechanic should check the injection pump's pressure output, timing, and internal condition.
* Fuel filter: Even a new electric pump can't overcome a clogged fuel filter. Replace the filter; it's cheap and a common source of problems.
* Injection pump timing: Incorrect injection timing can cause surging. A timing check is crucial if other causes are ruled out.
* Fuel lines: Check for leaks, kinks, or restrictions in the high-pressure fuel lines leading to the injectors. Collapsing or partially blocked lines can cause surging under load.
2. Air Intake System:
* Restricted air intake: A clogged air filter, dirty MAF sensor (if equipped), or other restriction in the intake system can cause erratic fuel/air mixture and lead to surging. Clean or replace the air filter, and check for any other obstructions.
* Vacuum leaks: Vacuum leaks in the intake manifold or vacuum lines can disrupt engine timing and fuel delivery, causing surging. Carefully inspect all vacuum hoses and connections for cracks or leaks.
3. Engine Mechanical Issues:
* Governor issues: The governor controls the engine speed. A faulty governor could cause unpredictable changes in fuel delivery, resulting in surging.
* Turbocharger issues: If your 6.2L has a turbocharger (some did, some didn't), a malfunctioning turbo (wastegate sticking, internal damage) could cause inconsistent boost pressure, leading to surging. Listen for unusual turbocharger noises.
* Injection pump problems: As mentioned before, this is the heart of the fuel system and problems with plunger wear, timing, or internal leaks are prime suspects in these older engines.
* Exhaust restriction: A severely clogged exhaust system can back up pressure and cause surging.
4. Electrical Issues (less likely, but possible):
* Wiring harness: Look for damaged or corroded wires in the engine bay, especially those related to the injection pump or other fuel system components.
* Sensors: Though less common with this era of diesel, problems with sensors (if equipped, like a MAP sensor) can cause erratic behavior.
Troubleshooting Steps:
1. Fuel Filter Replacement: Start here – it's the cheapest and easiest check.
2. Inspect Fuel Lines: Look for leaks, kinks, or collapses.
3. Check Air Filter: Ensure it's clean and unrestricted.
4. Listen Carefully: Pay close attention to any unusual engine noises (knocking, whistling, etc.). These can provide clues.
5. Consult a Diesel Mechanic: This is a complex system; a qualified diesel mechanic with experience in older 6.2L engines will have the tools and expertise to properly diagnose the problem. They can perform compression tests, check injection pump pressure, and perform other diagnostics.
Don't attempt major repairs yourself unless you have extensive diesel engine experience. The injection system on these engines is high-pressure and requires specialized tools and knowledge. A misdiagnosis could lead to further damage.
