2.7TT engine troubles.

2.7 V6 30v biturbo - 251bhp
2.7 V6 30v biturbo - 261bhp
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English expat
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Joined: Mon Dec 31, 2018 8:48 am

2.7TT engine troubles.

Post by English expat » Fri Sep 04, 2020 6:59 am

Morning all.

This is going to be a long post and i may have to edit/add as we go along as it has been nearly a year to this point. Full disclosure, i used to be a time served mechanic at the beginning of my career (nearly 25 years ago now), I got out of the trade late 2000's.

We have a late facelift avant which had been perfect. Last November the car developed a random misfire one morning (we commute by bike so don't drive very often, approx. once every 3 weeks).
After a little diagnosis i realized that one of the ignition amplifiers on the airbox had given up. This was tracked by swapping the coilpacks around to see if the misfire changed which cylinder it was affecting. It didn't, so the amplifiers were swapped and the miss swapped banks.

2 new amplifiers were ordered from Audi and fitted. This is where it starts getting expensive.......

We have another vehicle on the drive by the house and the far end of the drive is next to a large hazelnut tree. The car was parked there whilst we didn't use it and whilst changing the parts (after work in the dark). I didn't notice an accumulation of hazelnut shells littering the engine bay in little piles..........

Turning the car over to start i suddenly got the high pitched whirring that signifies loss of compression. At that point i stopped and waited for the weekend to throw some light on the matter. Long story short, a mouse had decided that the engine bay was a perfect place to store the food required for next winter, It had even managed to get into the timing belt cover and the organic matter between the timing belt and the bottom pulley had caused it to jump.

Pushed the car into the garage and once stripped down i could see that on both banks we had a slight interference between valves and pistons. I knew it had jumped at the bottom as both cams timed up correctly with the tool but the crank pin would not locate. Knowing that damage had already been done i gently turned the car over using a spanner on the cranknut until the crank pin would locate. The cams were still timed relative to each other but they had both jumped by 90° compared to the crank. The little oval plates were aligned up/down rather than left/right.

The heads were taken to a local cylinder head company and we went for a total overhaul. All new valves, tensioners etc. Once returned I built the engine back up. Crank pin correctly located, cams timed with the bar, all 4 marks on the cams lined up with the arrows on the heads and the correct number of links between the sprockets.

All new gaskets, bolts and ancillaries like the spiderhose , after-run pump etc.

Turned the engine over by hand twice and all marks lined back up. Primed the oil system by winding the car on the starter with plugs out as instructed by machine Shop. Went for start and no joy, no chain clatter, no loss of compression just no start. I checked the car with Vagcom and the only errors were implausible cam sensor signals.

This gave me the fear as i assumed that they wouldn't both go bad at the same time and this is where we had started a long time ago when the belt jumped. Stripped back down to the service position to recheck all timing marks. All are perfectly lined up. This reassured me as the hardware must be correct.

Rebuilt and tried again after clearing codes. No start and only the cam sensor signal error again. I then ordered two sensors on the off chance that they were indeed the cause of the problem. Again, no joy, same implausible sensor signals.

I have the 5v and the 10v at the sensor plugs that i believe i should with ignition on. Car turns over beautifully, i can smell fuel and i have spark but the closest thing i can liken it to is when a dizzy is reinstalled 180° out. It doesn't cough or try to fire.

After much googling i can't figure out if the car wont start if it doesn't know where the cams are or if it would simply miss?

I have spent so many hours on this now that i would like some advice. I have checked basics two or three times. Timing tools refit correctly. Fuel is priming, spark is present.

Are there any measuring blocks i should check in Vagcom when cranking? I must be close but just chasing my tail.

Will edit to add pictures during the course of the day.

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