Engine knocking noise
I have a 2012-registered Picasso C4 1.6 HDI with 14,000 recorded miles from new and a full Citroën service history. If I accelerate through the gears into either third or fourth and let my foot off the accelerator at between 1700-2500rpm while it is still in gear, there is a distinct ticking noise which disappears at around 1700rpm. This also happens when changing down from, say, fifth to fourth or fourth to third. The noise is constant in frequency and intensity, and it is not present when coasting or if the engine is revved in neutral. I have not detected the noise in either fifth or sixth gear within the same engine speed range, but this could be due to the fact that wind noise is masking it.
The supplying Citroën dealer has looked at the vehicle on three separate occasions and run exhaustive diagnostics, with no recorded fault codes or obvious mechanical defects. On the last visit, he arranged for a technician from Citroën to be present, who diagnosed a faulty injector. This was replaced and the problem appeared to go away, although it returned it some 20 miles later.
The dealer has assured me there is no fault in any of the fuel management or delivery systems and any other areas of the engine. However, while performance and fuel economy are more than acceptable, I can’t believe such a fault defies identification, especially when it is so noticeable. I want the dealer to look at the car once more, but would like some pointers or advice before they embark on a series of repeat checks. Nick Dring
You will appreciate that, without hearing the noise, I can only surmise what the cause may be. The injection system on your Citroën is very advanced and uses three injections per cycle. This consists of one very short pre-injection, then the main injection and then one short post-injection. This complex cycle only begins at 1700rpm; prior to this, the injector gives only the standard single shot injection. As your noise occurs at 1700rpm, this suggests the problem is with the injectors. Although it could be one or more of the injectors at fault, it might also be a software problem.