I own a 2008 Insignia with 98,000 miles now recorded. I recently got the cambelt changed and also had to get new camshafts/bearings/housing/seals etc. About two to three weeks later, the car would intermittently stutter/shudder when in 5th/6th gear at about 50 to 60mph and going uphill. I took the car back to where I had the repairs carried out to see if it was in any way related but, of course, the fault did not manifest itself when out on a test drive with the mechanic! I asked when the last fuel filter had been changed, as this had been the garage where the car had been regularly serviced. That turned out to be 73,000 miles ago. It should have been changed every 20,000 miles, so I got that changed. I also added into the fuel an injector cleaning product, which initially seemed to help, but the problem still persisted. I went to another garage where the air mass sensor was checked, the fuel pressure was checked, the car was put onto the diagnostic machine and no faults were recorded on the ECU. I have also changed the air filter. This all seems to have helped in terms of the general performance of the car, but the problem still persists, albeit in an intermittent form. I am told that the engine in my car is from the Alfa Romeo stock. I am also told that there could still be some dirt in the fuel tank, and so when the tank is at a low level, I will take it to the garage to have the tank cleaned out. Is there anything else that could be causing this problem? I have had no trouble otherwise, and when the car drives it goes well, and Vauxhall certainly did improve on the old Vectra. I would appreciate your views and comments and direction as to how this may be remedied. Or perhaps this is a known fault on diesels?
Hugh Scott, N Ireland

PS: I’ve recently become an avid reader of DC, which is an excellent read for diesel owners.

This is a bit of a strange one Hugh! Do you think maybe it was happening occasionally before the cambelt change and camshaft work, or are you quite sure it was not previously evident? Why did it take two to three weeks to appear, one might wonder? Is there any suggestion of fuel starvation at any other time, like foot down hard on the level, at high speed? Such circumstances draw quite heavily on the fuel supply and I quite understand why you had suspicions of the fuel filter and had it replaced. I also concur with your suspicions of possible dirt in the fuel tank. My suspicions veer towards the MAF (mass air flow) unit, which can just get dirty, but not necessarily throw up a diagnostic fault. But some of the favourite faults for poor running with these CDTi engines are:

1 Clogged EGR (exhaust gas recirculation) valve;

2 The MAF;

3 The “swirl valves” in the inlet manifold, where the actuator rod can fail, or the whole inlet manifold system can, like the EGR valve, get clogged up, due to short runs and not enough hard exercise – a bit like our arteries do later in life!

4 There could be some obstruction or split in a high pressure turbocharger inlet pipe, but I think the symptoms would be more severe than you are describing.

Now, it doesn’t sound to me as if you are proposing DIY work, but rather that you would like some ideas before you go off spending more money at a garage and not getting a definitive solution. Before you do that, for the modest cost of a tenner or so, (and I do know that you’ve used another product already) buy a bottle of Millers Diesel Power Ecomax, put the recommended double dose of it in your next tankful of fuel, and go out and do a decent hard run. I get so many letters where similar problems are cured with such simple action (particularly if you use supermarket fuel, and don’t do regular long runs) when it can be any of several things – MAF, EGR, etc. If this doesn’t improve things, then go and find a diesel specialist who will deal with lots of cars that use the same engine, and see what they say. It’s probably nowhere near you, but I’ve had great reports of Scotts Garage in Dundonald, BT16 1QQ, and it might be worth a decent drive to visit them. I hope these suggestions are of some help.

Thanks for your kind words regarding Diesel Car, for which you can mostly thank our Editor, and now magazine owner, Ian Robertson. (And our first rate contributors and back-office team, too – Ed)
Doc Diesel