Doctor Diesel

Oh my, Gordon

I have just returned from France, where my EGR decided to give up the ghost. This meant that it had to be changed in Poitiers. On having this done, I noticed that the engine stuttered all the way back to my St Malo home, as if it were a petrol engine suffering from an ignition lead breakdown. I checked the car into my local garage, who changed the air mass flow valve (MAF), but the problem still exists, although the effect is less jerky. The EGR valve appears to hunt, rather than producing a graduated flow, but does not produce any adverse readings on the carís instruments, or the external fault finding equipment. Please, have you any ideas before I end up having to consider replacing the valve once more? The car is a SEAT Altea XL 1.6 TDI (A DSG, as I later discovered! Funny you didn’t mention that Gordon!) with 34,000 miles on the clock. 




Hello Gordon. Not sure how you came up with your thoughts on the hunting EGR valve ñ was it maybe from your “external diagnostic equipment?” The symptoms are indeed somewhat similar to failure of the EGR cooler, which unfortunately is not an uncommon problem. Was the MAF change just a shot in the dark by your local garage? Did they know what they were doing? I’m taking the garage to be a small independent one, and not your local SEAT dealer. If you want to keep trying for a DIY cure, you could try using some EGR cleaner, like Wynnís. But a proper diagnostic check must surely come up with a fault code and some suggestions, if the engine is in this state. You can’t keep changing various bits hopefully, without some more solid evidence of where the problem lies. My only added thoughts are the possibility of a low pressure fuel supply pump problem. The engine might therefore work better with a full tank of fuel, although that won’t of course sort the problem. But it does sound like a fuel supply problem to me. Do you have any black smoke, which would mean plenty of fuel, but faulty combustion? 


Best regards, 

Doc D


Gordon replied: 


Thanks Doctor for your advice. Nothing is coming up on the diagnostic check, according to the equipment. Although the garage is not a dealer, he is a SEAT specialist. I agree that the air mass valve is clearly not the problem, but here are some more symptoms: At 70 to 80mph, the engine surges and can only be stopped by a quick jab down on the accelerator pedal, or by taking the foot off. At low speed and gentle acceleration, the engine surges and sounds like a washing machine making a repetitive shoosh-shoosh sound. At 50 to 60mph the surging reduces, but is still apparent, especially on the overrun, or gentle acceleration. Acceleration from standstill can be variable, sometimes catching out the automatic transmission into changing up later than usual ñ i.e. over-revving before changing up. 


The EGR valve had obviously begun to fail some 400 miles before it finally gave up, as the coil sign, and then the engine symbol, indication lights came on, with limp-home mode then engaged. Thinking that it was the lambda sensor, I eventually got it to clear by going into manual and repeatedly accelerating sharply. I had done about 250 miles at 80mph at the time. It was only much later that the symptoms re-appeared and the total failure occurred. Prior to the final failure, I refilled at a small independent filling station about 150 miles before failure, so this may well be the added potential problem of dirty fuel. I refilled the tank and added Redex fuel cleaner to boot, as soon after my return from France. (Redex in the boot? It goes in the tank Gordon!) It looks like I have got a double whammy of problems! 


Best wishes, Gordon


I’m actually beginning to wonder if it’s not a DSG transmission problem now. Are you sure you didn’t put some petrol in the tank, and then try to cover it up by putting some diesel on top? Are you sure you haven’t got an Indesit washing machine under the bonnet? How about slowing down a bit, when your engine is obviously very sick? I’m really a bit lost on this one Gordon. Doc

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