A diesel lives or dies by its fuel system. The injection system pressurizes fuel and sprays it into hot compressed air at exactly the right moment; there is no spark plug to cover for a bad spray pattern. When an injector or pump starts to fail, the engine tells you through smoke, noise and lost power. RDI Power tests diesel fuel systems at our Brooksville shop on everything from Power Stroke pickups to Class 8 tractors, and our technicians can start the diagnosis at your yard.
What makes up the system
- Lift or transfer pump: pulls fuel from the tank and feeds the high-pressure side.
- Fuel filters and water separator: most diesels run a primary and a secondary filter, sometimes with a screen at the tank, and a separator that collects water so it can be drained.
- High-pressure pump: builds injection pressure, or on HEUI engines, pressurizes engine oil to fire the injectors.
- Injectors: atomize fuel into the cylinder, timed by the engine computer on modern engines.
- Lines, rails and return circuit: carry fuel at pressure and bring excess back to the tank.
4 injection designs we work on
| Design | How it works | Examples |
|---|---|---|
| Mechanical pump | A cam-driven pump meters and times fuel to each injector | 12-valve Cummins with the Bosch P7100 |
| HEUI | High-pressure engine oil fires each injector | 7.3 and 6.0 Power Stroke, DT466E, VT365 |
| Unit injector | Pump and injector combined at each cylinder, driven by the camshaft | Caterpillar 3406E, C15 |
| Common rail | A pump keeps a shared rail at high pressure; injectors open on command | Cummins 5.9 and 6.7, Duramax, 6.4 and 6.7 Power Stroke |
Water is the main enemy
Diesel fuel holds more water than most people expect, and Florida humidity adds condensation in tanks that sit partly full. Water that gets past the filters corrodes steel parts, scores pump internals and causes injectors and metering parts to stick. Draining the separator and changing filters on schedule prevents more fuel system repairs than anything else. We cover more causes in the top reasons diesel injectors fail.
Symptoms worth a visit
- Hard starts or long cranking, hot or cold
- White smoke (unburned fuel) or black smoke (too much fuel or too little air)
- Rough idle, misfire or a new knock
- Power loss, or a rail pressure or fuel pressure code
- Oil level rising between changes
How we test it
- Supply side first. Fuel pressure from the lift pump, filter restriction and a check for air or water in the fuel. A starved high-pressure pump looks like a bad pump.
- High-pressure side. Desired versus actual rail pressure on common rail engines; injection control pressure and FICM voltage on HEUI engines.
- Injector by injector. Balance rates, cylinder contribution and return flow (leak-off) tests point to the specific injector that is failing.
- Root cause. If an injector failed from contamination, we find the source before installing new parts.
Fuel system repairs
Repairs range from filters and a lift pump to replacing injectors, a high-pressure pump or contaminated lines and rails. On many common rail engines, new injectors must have their trim codes programmed into the engine computer. When a high-pressure pump sheds metal, the debris travels downstream, and a lasting repair cleans or replaces everything it reached. We use Bosch and Alliant Power components matched to the engine.
If your diesel is smoking, knocking or slow to start, book a fuel system diagnosis. You get a digital inspection with test results and photos before any parts are ordered.