S40 (New) Engine 2.0D : Poor performance, acceleration surge

[SD40]

The S40 story.
The troubles of a 2008 S40, 2.0 – 136BHP Diesel. Euro 3 – D4204T. 184 000 mls.

Maybe these issues could be stickied - or made more obvious if i have missed them.

1) About 5000 miles ago I noticed that during hard acceleration in 5th and 6th gear the acceleration was surging slightly, almost pulsing. It was very slight, and I didn’t do anything about it, no fault lights shown, nothing else unusual.
2) The above continued for the following 500-1000 miles, becoming more noticeable over the period, but still no substantial effect on performance – but I did notice an increase in fuel consumption, 2-3mpg.
3) I changed the fuel filter, oil filter, changed the oil.
4) The surging seemed better, but it didn’t go away completely.
5) I tried an air filter change – the engine felt like it was either being restricted in some way or I was starting to think that the boost was dropping off. I had a universal K&N cone filter (thinking, its about time the car was modified). So, I fitted that and the result was not good. The diesel induction noise was not great and the performance seemed noticeably worse – that’s strange I thought.
6) Removed K&N, car felt better – but again not back to what it was… going backwards not forwards with this situation! I called 3 suppliers of these filters, none admitted that these filters cause any issues.
7) So, the car was still surging during acceleration as in 1. But performance felt poor now as well – there seemed to be a lack of torque in the midrange especially.
8) Deleted the egr – disconnected the harness and its run without showing a dashboard fault ever since, starts better, runs better, fuel consumption better by about 4+mpg.
9) Trawled the forum(s), as usual, many, many similar issues. About 90% of the posts had one or two replies; probably about 1% of what I looked at went into some detail and gave a possible solution. The information is out there, but its so hard to find it and then collate it into something useful.
10) We are at about 4000miles since the start of the issue now, the car is more often than not running badly. Its rare that it performs anything like it should. It will cruise at 70ish OK (48mpg). But the acceleration is terrible and with a couple in the car it struggles to maintain any speed up a long hill… maybe half a mile. Even dropping a gear (or two) make little difference.
11) I looked at the vacuum and pressure systems next – vacuum relative to the boost control and the pressure side relative to the turbo pipework, intercooler, inlet manifold.
12) Could not find any leaks – anywhere. Checked for splits, cracks, loose clips etc. physically checked all of the hoses/pipes apart from those that go around the rear of the block.
13) I changed the intercooler for an Airtec Focus ST one – so that’s ok.
14) Sensors changed -
(a) MAF
(b) MAP
(c) 2 x Boost control solenoids.
(d) Wastegate position sensor in the shed… looks to be a pig to fit.
15) So, about a week ago I bought VIDA DICE – pain to set up but that seems to be normal – a list of non critical faults shown – took a picture of them and deleted the whole lot. Reasoning was that I don’t care about the previous faults, only the present issue, it’s the current faults in this case I need to see.
16) Only fault that shows now is high output egr – its disconnected.
17) All faults clear – all electronics modules green.
18) Car runs about 70% as it should, still lacking torque, there is still an issue somewhere, but a lot better.
19) Clearing the codes seems to have resolved many issues, but I do still have a fault – I still think it’s a boost issue.
20) Up to date now – still a loss of torque, I intend to get VIDA connected and plot a graph with RPM, accelerator position, boost, map and speed.
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