If the pump runs well and the only complaint is an external leak, a reseal, replacing the seals and gaskets, may be enough. If the pump also has hard starting, low power, smoke, surging or high mileage, a reseal won’t fix those, and a rebuild with calibration is the better repair. Either way, don’t ignore a leaking pump. Fuel on a hot engine is a fire risk, a leak can let air into the fuel system, and on some pumps a leak you can’t see is diluting your engine oil.
Where injection pumps leak
On mechanical rotary pumps
- Throttle shaft seals: one of the most common leak points as pumps age
- Top cover and governor cover gaskets
- Fittings and line connections
- Shutoff solenoid seal
- Drive shaft seal, which can leak fuel toward the engine
On inline pumps
- Delivery valve holders and their seals
- Governor housing gaskets
- Fittings and lines
- Internal leakage into the pump’s camshaft area, which on engine-oil-lubricated pumps returns to the crankcase and raises the oil level. See diesel fuel in engine oil.
On electronic and common-rail pumps
External seals and fittings can leak like any pump. On common-rail systems, leaks at high-pressure fittings and lines are a serious safety hazard. Never feel for a high-pressure leak with your hand. See high-pressure diesel fuel injection injury.
Why a small leak matters
- Fire. Fuel weeping onto hot exhaust components, or atomized from a pressurized fitting, can ignite.
- Air entry. A seal that leaks fuel out can let air in under suction, causing hard starting and rough running.
- Oil dilution. Internal leaks into an oil-lubricated pump thin the engine oil.
- Dirt. Wet surfaces collect grime that can enter the system during later service.
- The environment and your floor. Diesel on the ground doesn’t go away by itself.
Reseal vs rebuild
| Situation | Reseal | Rebuild |
|---|---|---|
| Pump runs well, external leak only | Often enough | Not required |
| Leak plus hard starting or low power | Won’t fix it | Recommended |
| Leak plus surging or governor issues | Won’t fix it | Recommended |
| High mileage or hours, never serviced | Short-term | More durable repair |
| Internal leakage raising oil level | Won’t fix it | Needed |
| Pump has been tampered with or adjusted | Leaves settings unknown | Calibration restores spec |
A reseal still requires care. Disassembling a pump to replace seals can disturb settings, introduce dirt, or reveal worn parts that weren’t apparent from outside. A reseal performed on a test stand can be verified; one done on the bench at home can’t.
About DIY reseal kits
Seal kits are sold for many pumps, and experienced owners do use them. The risks are real, though: incorrect assembly, damaged shafts or bores, contamination, and disturbing governor or fuel settings that can only be verified on a test stand. If you take that route, work clean, follow the procedure exactly and be prepared to have the pump calibrated if it doesn’t run right afterward.
Your next four steps
- Identify the leak safely. Note where fuel was present with the engine off. A trained technician should use the engine maker’s approved isolation and depressurization steps before touching high-pressure components; never probe a live leak with cardboard or hands.
- Check the engine oil level for signs of internal leakage.
- Note any performance problems alongside the leak.
- Photograph the pump tag before anything comes off.
Questions to ask before a reseal
- Does the pump run well apart from the leak, including hot starts and full power?
- Has the pump been opened or adjusted before?
- Is there any sign of internal leakage, such as a rising oil level?
- Will the resealed pump be checked on a test stand afterward?
- What parts beyond seals might the shop recommend once it’s open, and will they call before replacing them?
If the honest answer to the first question is “not really,” a reseal will probably leave you with a dry pump that still runs poorly.
Further technical reference: Bosch: Diesel Repair Network and supported component service. Use the exact engine/injector/pump service information for applicable procedures and limits.
Get the right repair for your pump
Diesel Control Technicians reseals, repairs, rebuilds and calibrates injection pumps for trucks, tractors and equipment. Send a photo of the pump tag, a note on where it’s leaking, and any performance symptoms, and we’ll help you decide whether a reseal or a rebuild makes sense. For the full rebuild picture, see what happens in an injection pump rebuild.
Ask about pump or fuel-system service: Request a mail-in component review with the pump tag, engine application and diagnostic findings. Confirm supported testing or repair, intake terms and current timing.