Engine speed sensor/Crank position sensor FSI

For a change this is a fix rather than a problem and I hope it helps a few people with some erratic running problems.

I was getting a intermitent warning on the sensor in the last few weeks and the car refused to start twice but now that is has been fixed it has cured a myriad of problems:
Erratic idle - fluctuates about 50rpm, easily visible on the rev counter
Surging at motorway speeds, especially around 75mph
No throttle respone periodically when at motorway speed. The car doesn't slow down but neither can you accelerate, lasts for a few secounds
Also the consumption has improved, 38mpg on the way there and 48mpg on the way back! Was a slower trip back (150 miles each way) but 5mpg improvement would be realistic.

Now for the pain! Audi wanted £450 to change the sensor and an additional hour for diagnostics.

I had a look at changing the sensor myself and managed to trace the sensor from the where it clips into the harness to where the sensor is mounted. The wiring clips in under the driver-side inlet manifold and as is possible to get to. The actual sensor is mounted on the crankshaft on the clutch side and is not visible and neither will you be able to feel it. Elsawin is not that useful.

I took the car to my "local" garage in Birmingham (I live in London hence the 150 mile roound trip). Up on a ramp, remove the driver-side driveshaft from the gearbox to allow a x-shaped plate to be removed that is mounted onto the bottom of the inlet manifold. With the plate removed he could follow the wire into the gearbox housing. There is a rubber bung to stop water ingress (remove this) and you can get an allen-key onto the sensor. Replacement is the reverse.

Sorry I have no photos but unless you have access good access under the car it may be best left to someone who has.

Total cost, £80 for the sensor from Audi, 1.5 hours labour to fix.

If anyone is around the Birmingham area or is willing to travel I recommend Martyn Billings Automotive. He has looked after my cars for 12 years. 01902 497 985.

He has also done the FSI flaps and cambelt on my car so has experiance of the worse jobs on an FSI.

Cheers

Alex

Hi Alex, Thanks for your post. I wouldn't have been able to install a new G28 sensor without it. My 1.6 FSI has been giving misfire warnings for a long time, also a warning about an inlet air leak. The idle speed has been fluctuating by 50rpm. More recently I've experienced problems with surging and a flat spot at 2500-3000 rpm when the engine is hot. Then yesterday the problems got worse with misfiring and juddering at almost all engine speeds. The idle speed was all over the place - 900 -1500rpm. The engine was difficult to start. I checked the fault codes this morning and found G28 implausible signal and G28 no signal, so there was no delaying the installation of a new crankshaft sensor. I'm quite capable DIYer with the toolkit to match - but I can tell you this job is tricky. The Audi manual was pretty much useless - it shows a couple of drawings of the position of the G28 sensor viewed when the engine has been removed from the car, and in at least one of them the engine has been inverted so not much help in finding the G28. You'll find the G28 is mounted in an aperture in the engine block casting so that the tip of the sensor is close to the flywheel (i'd guess it picks up the speed or position of the ring gear teeth on the flywheel). This aperture is very close to (and hidden behind) the driver's side drive shaft. It's necessary to disconnect the inboard end of the drive shaft so it can be moved sideways a little (I'm sure it would have been easier if I had removed the drive shaft entirely). Also the inlet manifold support bracket (or X shaped plate that Alex refers to) can then be removed after disconnecting or removing several items of vacuum pipework mounted on the aft side of the engine block (including the PCV valve/oil separator). A mirror and a good lamp is needed to see the rubber bung over the aperture. As Alex has said, you can then follow the cable that comes out through the bung, along the back of the engine to a connector at the cambelt end of the engine. It's relatively easy to remove the bung and feel around in the depths of the aperture for the head of the securing bolt and to remove it with an Allen key, but when you do this you must commit to memory the relative positions of the head of the bolt, and the wiring connector, and their position in the depths of the aperture, because you will be working by feel when you install the new sensor. It took me an hour under the car, in the cold, to get the new sensor in position (it would probably have been quicker to remove the driveshaft entirely). One other thing, if you decide not to remove the driveshaft entirely, put a plastic bag round the inboard end to reduce the amount of CV joint grease that will otherwise get spread around. My car's G28 warnings have now cleared. I'm left with the a slightly steadier idle speed and the warnings about an air leak. The misfire and juddering at all engine speeds has gone but there is still a flat spot at 2500-3000rpm when the engine is hot. I intend to investigate this further in the new year. My gut feeling is that it isn't due to the air leak (which seems to be very small and can't be traced by spraying WD40 around the length and breadth of the vacuum pipework). The camshaft position sensor has already been replaced. I could easily be wrong but I suspect there is a problem with the VVT - possibly the N205 valve isn't working properly. Most of the problems I've been experiencing with this engine occurred after it had overheated - perhaps the sensors were damaged?