S4 broke down and won't start

[merlin's S4]

On Friday evening something happened while pulling away normally from a standing start. I think I heard something as if something had fallen off which may or may not be significant but the S4 instantly ran horridly. The engine wouldn't rev, was popping and I couldn't get passed about 30 MPH. I could smell the exhaust fumes from I suspect rich running. I nursed it to the roundabout at the top of the hill where it stalled and wouldn't restart. It appeared to turn over normally and I couldn't see anything obviously wrong or missing so I got it towed back home.

My code reader listed these codes:

00513 - G28 Engine speed sensor
00514 - Ignition timing G4 Crank position sensor no signal
00515 - G40 Hall Sender
00537 - Lambda sensor
00561 - Mixture adaptation

Now I'm guessing that the Lambda and Mixture codes were caused by the rough running and the G28 code is ever present.

My immediate thought was that the timing belt had slipped but upon investigation today this doesn't appear to be the case.

Can anyone shed some light before I investigate further? Thanks!!

[UrS4boy]

Look to see if the G4 timing pin is still there:

http://forums.quattroworld.com/s4s6/msgs/51259.phtml

Check the condition of the G4 and G28 sensors:

http://forums.quattroworld.com/s4s6/msgs/20986.phtml

Check the condition of the G40 cam sensor:

http://forums.quattroworld.com/s4s6/msgs/22580.phtml

The engine will not restart until all three, the G4, the G28 and G40, are in working order.

[twoqu]

The crank position fault might indicate that the timing pin on the back of the flywheel is absent! Would be worth physically verifying that.

[K Simmonds]

The noise you heard 'may' have been the timing pin coming away from the fly-wheel, which would explain the 00514 - Ignition timing G4 Crank position sensor no signal code. Obviously a failed crank sensor would give the same code.

[merlin's S4]

Thanks guys! I'm leaning towards the Flywheel Pin idea too. Is the best way to inspect through the starter motor hole or can you feel the pin through the timing window at the top of the bell-housing?

[mcandmar]

Either will work, i would just remove the sensor and have a look in as its quicker than removing the starter.

[UrS4boy]

Either will work, i would just remove the sensor and have a look in as its quicker than removing the starter.

But you can't weld a new one on through the sensor opening.

[mcandmar]

But you can't weld a new one on through the sensor opening.

I cant weld so

[UrS4boy]

I cant weld so

Too small for JB Weld (epoxy) too.

[merlin's S4]

Well done guys!! The timing pin has come off the flywheel.

Any advice regarding fixing it? I may have another pin on a spare flywheel but if I don't can I have one made? And what is the best way to stick it back on?

[andyg plym]

this is a gearbox off job isnt it?

[merlin's S4]

Not if I can help it!! I know it's been done through the starter motor window.

[UrS4boy]

Well done guys!! The timing pin has come off the flywheel.
Any advice regarding fixing it? I may have another pin on a spare flywheel but if I don't can I have one made? And what is the best way to stick it back on?

Ha! Is there a prize? I called it first.

I think we (AAN, ABY and ADU owners) need to start thinking about a pre-emptive rewelding of that timing pin - before it comes off. It can be welded through the starter hole (been done locally to me). Needs two people, one to press the pin into position with a wooden dowel and the other to do a tack weld and then final weld.

The details about the size and shape and location of the pin are provided in this post:

http://forums.quattroworld.com/s4s6/msgs/51259.phtml

[dspl1236]

i MIG'd my pin back on via starter hole held with vise grips after i finished my v8q 016 swap.... sucker broke on the first start and rev back in '06.... 4 owners later its still going

[twoqu]

It also unfortunately confirms that if the pin goes the engine starts to die immediately!
However we know from another members car that if the actual sensor is unplugged the cars still functions. Which is a bit illogical as you would have expected the no signal condition to have the same effect. Evidently, somehow the Motronic is able to tell the difference between a failed sensor and a missing pin!

Not sure if you have removed the starter yet. Perhaps the pin is laying around the bottom of the gearbox. If so you could attempt a repair. If you remove a pin from a good flywheel and cannot effect an on car repair then you would have to remove the flywheel anyway! Looks like the consolidation of an existing pin in the right position would be the best practice but more work!