Prolonging diesel injection pump life

Posted on August 4th, 2017 by Rob Marshall


I hope that you would not vote this blog as the most boring topic ever to appear on the Internet but, if you wish to reduce the risk of having to stump-up an eye-watering sum for a new replacement diesel high-pressure pump, you may wish to read on…

Even the most disinterested car owner could not have failed to notice the fairly bad press that diesel cars have received recently. Yet, modern, high-pressure, common rail diesel engines remain technological marvels. Their outputs are impressive, they are hugely fuel-efficient and, yes, even when we try to forget the ‘DieselGate’ and car manufacturers’/governments’ skulduggery, overall exhaust emissions are remarkably low.

To achieve this, modern diesels have become very complex and many parts are precision made. Unsurprisingly, they have become very expensive to buy brand-new but at least reconditioning companies have sprung-up, which can rebuild the original parts for a fraction of the cost of new parts.

In this blog, we shall look at the high pressure pump specifically, because it tends to be the most expensive part to renew. Its job is to pressurise diesel fuel to around 2,000PSI (for context, a typical car tyre is inflated to 30PSI) that permits the fuel injectors to pulse fuel into the engine with the utmost accuracy. Unsurprisingly, they can fail and cause the engine to either run badly, or stop running completely, but there are things that you can do to prevent a hefty repair bill. However, the fault could lie with cheaper parts of the system, such as electrical sensors, so be wary if you are told that the pump is faulty, without other causes being investigated first.

Main causes of pump failure and how to avoid them:

  • Running out of fuel: Certain diesel pumps (such as the Bosch CP4) can be damaged severely by incorrect bleeding, which is required after the fuel tank runs dry and is refilled. Some vehicles require diagnostic equipment to be bled correctly. To be safe, avoid running out of diesel!
  • Modifications: Certain engine tuning raises the pump pressures and causes thermal overheating, which can shorten its life. Also, certain cetane-boosting diesel fuel additives, if not dosed correctly, affect the lubricating quality of diesel fuel, which increases internal pump wear.
  • Misfuelling: Should you fill-up with petrol accidentally, the pump can be damaged before the engine is even started. This is because petrol possesses zero lubricating qualities for diesel fuel pumps. Do not even turn-on the ignition; seek advice and organise transportation, so that the fuel system can be drained professionally.
  • Poor maintenance: Diesel fuel filter housings require annual drainage of corrosion-causing water. Regardless of manufacturers saying that they can be left for longer, I advise replacing the fuel filter cartridge annually. Use good quality filters, as poor-quality substitutes tend to fall apart and the fragments damage the pump subsequently.
  • Fuel contamination is the top cause for failure. Therefore, avoid filling-up your car with unknown diesel from a drum. If you use a fuel can, ensure that the diesel has been filtered and that you know its original source. Apart from being illegal, unless duty has been paid on it, never use other fuels in your modern diesel, including pure bio-diesel, unless you are buying it from a credible supplier that warrants that the fuel will not damage the delicate pump.