Complaining that his BMW 520d was emitting a constant sound of rushing air, the owner was surprised to discover that the problem was down to a blocked diesel particulate filter (DPF). The rush of air was the sound of the exhaust gases fighting their way out via a small leak in the front flexi-pipe. The unit had long since passed the stage where a regeneration would have helped and replacement was going to be the only option.
In theory, this looked like a quick and easy task. Bolted into place with four nuts and bolts at the square flange on either end of the unit, it only needed the bolts to be undone and the DPF to be dropped out. But the effects of rust had been at work, so the nuts refused to come undone and the bolts were stuck fast in the holes, although the use of a grinder and an air saw helped ease the job a little.
Once the new unit was fitted, the sound of rushing air was no longer audible and the vehicle’s performance was also increased.
Once the DPF has been removed, the difference between the new and old filters is obvious.