Maitlandia
10-10-2017, 12:36 AM
Hello everyone,
I had this problem and thought I could work it out but in the end I fixed it without knowing it. My post is a bit long but its a long story!
The car is a low mileage 1.9 Tdi 66kW AGR engine with normal injection system. I changed the cam belt recently and, with a friends help, checked and reset the injection timing with VAG-COM. I was a little disappointed to find that although I had reset the cam timing and fine tuned the injection timing and the car started easier and ran smoother, there was zero improvement to the mpg which runs around the 59/60 mpg mark - I was hoping for more. Anyway, not too long after, and it was more of a feeling that I was missing power but as the weeks went by I noticed a very definite 'hole' in the pull of the engine between 2,000 and 2,500 rpm. This got worse and worse i.e. the 'hole' spread out each side until it felt really underpowered and overtaking became 'interesting'. I fitted a boost gauge to the inlet manifold and found very little to worry about, there was 1.0 bar max which did not peak particularly quickly but I was getting full boost. OK, it wasn't the turbo, so what was it? I decided to take the inlet pipe off and have a look up what would be the throttle body if it was a petrol engine and was shocked to see the amount of carbon caked all over the EGR valve port. The carbon build-up must have reduced the inlet by a third at least. I took the EGR valve off and cleaned it all out and scraped as much oily grot off the inside of the inlet manifold as I could reach. That's gotta be it, I thought. No, it wasn't. Still the same. I also disconnected and plugged the EGR pipe to stop it working and building up carbon again and later bought two blanking plates and took the EGR link pipe off altogether. Meanwhile the lack of power continued. OK, maybe the anti run-on valve is closing at the wrong time so I ran the car with that pipe off. No, not that. OK, maybe the rest of the inlet manifold is choked up with carbon so I took that off. No, it wasn't badly restricted really. Sure it was gungy in there but not overly constricted, the backs of the valves didn't look pretty either but getting he carbon out of there was not going to be easy. In fact having loose lumps of carbon could end in tears so I figured, best to leave them alone. Whilst the inlet pipe to the turbo was off I twizzled the turbo shaft - nice and free and there was no axial play so I reassured myself the turbo was definitely OK. I also put a camera down the cold-air pipe to the air filter in case a family of wrens had taken up residence - no, all clear. Anyway, put all that back together and . . . no difference! Even worse if that was possible. Now the engine would not rev past 3,000 rpm and I could not coax more than 0.5bar out of the turbo. I even took all the pipes off the boost control valve so there was nothing controlling the turbo at all and still it would not go over half a bar! OK, maybe the cam timing has slipped? The sprocket is only on a taper, not keyed at all, I couldn't really believe it but maybe it has crept round? Checked that - no, perfect timing still. Finally, whilst the air filter cover was off anyway I thought I'd look at the mass air flow meter. I unscrewed it, looks fine but seeing as though it was out, I would just clean the wire with a cotton bud and brake cleaner which resulted in a slightly brown mark on the bud then, dejectedly, I put it all together again. The next time I drove it BINGO, power and boost restored - it was a very, very slightly dirty wire on the MAFM!
I had this problem and thought I could work it out but in the end I fixed it without knowing it. My post is a bit long but its a long story!
The car is a low mileage 1.9 Tdi 66kW AGR engine with normal injection system. I changed the cam belt recently and, with a friends help, checked and reset the injection timing with VAG-COM. I was a little disappointed to find that although I had reset the cam timing and fine tuned the injection timing and the car started easier and ran smoother, there was zero improvement to the mpg which runs around the 59/60 mpg mark - I was hoping for more. Anyway, not too long after, and it was more of a feeling that I was missing power but as the weeks went by I noticed a very definite 'hole' in the pull of the engine between 2,000 and 2,500 rpm. This got worse and worse i.e. the 'hole' spread out each side until it felt really underpowered and overtaking became 'interesting'. I fitted a boost gauge to the inlet manifold and found very little to worry about, there was 1.0 bar max which did not peak particularly quickly but I was getting full boost. OK, it wasn't the turbo, so what was it? I decided to take the inlet pipe off and have a look up what would be the throttle body if it was a petrol engine and was shocked to see the amount of carbon caked all over the EGR valve port. The carbon build-up must have reduced the inlet by a third at least. I took the EGR valve off and cleaned it all out and scraped as much oily grot off the inside of the inlet manifold as I could reach. That's gotta be it, I thought. No, it wasn't. Still the same. I also disconnected and plugged the EGR pipe to stop it working and building up carbon again and later bought two blanking plates and took the EGR link pipe off altogether. Meanwhile the lack of power continued. OK, maybe the anti run-on valve is closing at the wrong time so I ran the car with that pipe off. No, not that. OK, maybe the rest of the inlet manifold is choked up with carbon so I took that off. No, it wasn't badly restricted really. Sure it was gungy in there but not overly constricted, the backs of the valves didn't look pretty either but getting he carbon out of there was not going to be easy. In fact having loose lumps of carbon could end in tears so I figured, best to leave them alone. Whilst the inlet pipe to the turbo was off I twizzled the turbo shaft - nice and free and there was no axial play so I reassured myself the turbo was definitely OK. I also put a camera down the cold-air pipe to the air filter in case a family of wrens had taken up residence - no, all clear. Anyway, put all that back together and . . . no difference! Even worse if that was possible. Now the engine would not rev past 3,000 rpm and I could not coax more than 0.5bar out of the turbo. I even took all the pipes off the boost control valve so there was nothing controlling the turbo at all and still it would not go over half a bar! OK, maybe the cam timing has slipped? The sprocket is only on a taper, not keyed at all, I couldn't really believe it but maybe it has crept round? Checked that - no, perfect timing still. Finally, whilst the air filter cover was off anyway I thought I'd look at the mass air flow meter. I unscrewed it, looks fine but seeing as though it was out, I would just clean the wire with a cotton bud and brake cleaner which resulted in a slightly brown mark on the bud then, dejectedly, I put it all together again. The next time I drove it BINGO, power and boost restored - it was a very, very slightly dirty wire on the MAFM!