Citroen DS3 THP155 Engine after rebuild for excessive carbon build up

The DS3 THP155 is back from the garage. I have to say they may have took their time but they did a thorough job. Citroen were pretty reasonable in approving all sorts of things to be replaced but the reasons for most of them were unknown or vague. The obvious problem identified was excessive carbon build up on the back of the inlet valves and inlet tract with oil film build up on the inlet to the intercooler. This on a car with less than 12,000km or 7,500 miles on it!

To decoke it the head it had to be removed and chemically cleaned in the end. properly done but I wouldn't want to be paying for it to be done again myself.

So what was done? Well first a quick seafoam type clean which didn't work then a full removal and chemical clean of the head with the valves being removed relapped in to the head and fitted with new stem seals. All this just remedial cleaning work not fault fixing as stem seals not seen as a problem.

Lots of things were replaced. Turbo! Timing chain guides tensioner, cylinder head cover. Why well the answers were; timing chain might have stretched? The turbo was putting oil into the engine? the cylinder head cover has some PCV valves that may have not been operating properly?

The ECU was also given a software update and initialised adaptives which means the long term trims were reset to 0.