Ticking diesel

Can you advise me regarding a problem with my 1980 Mercedesbenz 207D campervan with the OM616 engine. When under load – generally full throttle – the engine makes a ticking noise a bit like pre-ignition on a petrol car. Backing off the throttle slightly makes it stop. Is this pre-ignition or something else and, if so, how can I fix the problem? James Robbins

Diesel engines suffer from a similar condition to pinking, which can be caused by either incorrect pump timing or failing injectors. Alteration of the pump timing is very rare and the most likely scenario is that the injectors are beginning to weaken and allow the diesel to enter the cylinder a fraction too early. This results in pre-ignition and the consequential pinking noise you are hearing.

Before taking any drastic action, I would first try using a different fuel – possibly one of the premium brands. It may be that the fuel you are using has a high ethanol content, which can give similar results. The use of a diesel additive may also help and this would be worth trying before taking the more expensive option of replacing the injectors.