1.8T Avant died on motorway, no brakes, cant start (does crank).... Help

[timgiles]

Hi all,

So for 6 years ish I have been looking after my A4 B6 1.8T Avant. I feel like I have changed a fait bit from most of the sensors, timing belt, etc... Last week I was driving home and on the motorway the car refused to accelerate, then started slowing down (brakes were no longer pressurised) and I needed to pull off. Car turned over but would not start up.

After a tow home and a few days trying to get to the bottom of what the cause is, I have the following:

No fault codes - I have tried removing the battery for a few minutes - still nothing (but the ECU is talking to my canbus computer)
First thought was fuel pump - it is pumping no problems - plenty of pressure
Starter motor is turning the motor/timing belt
Spark - all four spark plugs checked, sparking as the engine turns
When I now crank the engine, the sound is much higher pitch than normal
I thought possibly the cam sensor (hall effect) but that seems to be providing a signal as the engine cranks

I wondered if maybe the timing chain inside the engine could have snapped and is not opening/closing the valves correctly. Or if the engine speed sensor has died - could that cause the engine not to fire up?

Any other thoughts?

[fourringsrus]

Engine speed/crank sensor died recently on my 1.8t ( fitted in 225 TT,but essentially the same motor)
The car just died as if it was switched off, it would crank over happily but not fire up.
A friend came to tow me out of traffic, whilst on the tow rope I bump started the car in hopefulness and she ran fine.
Following evening the car did exactly the same thing at the very same road junction.
This time I bump started on the tow rope straight off rather than being towed around town without power steering or brakes.
The next couple of days she started on the key perfectly but I was not prepared to accept that things were fine.
After a bit of research on this fine forum ,it was clear that the issue was typical of the crank sensor failure, so I replaced that with new genuine as recommended by our friend "crasher" on the forum and she has been fine since.
There were other issues, such as rev counter messing about, but when I described the issue to "crasher" he was 100% that my issue was the crank sensor playing typical failure games.
I hope this is of some help, good luck

Stuart

[timgiles]

Ok replaced both the hall sensor and engine speed sensor. No change. I opened up the top of the motor, everything turns over on cranking. Can't see any damage. The chain is son, taught, etc...

The starter is still very high pitch compared to how it sounded before the incident. If the timing belt had skipped a tooth, what could I look for?

Anyone have any other thoughts?

[arman123]

Found this online if any help




do you get codes now? also, if its taking 30-40 seconds of intermittent cranking, it could be the the cam is off timing. i had this issue, it was off 1 tooth and would take a bit of cranking. but i got codes for intake cam advance setpoint not reached(cam over retarded)

if you want to check, take spark plugs out, set engine to cyl 1 TDC, remove valve cover and look at the chain side, on the exhaust and intake cam bridge, theres an arrow ^. count the number of chain links between the two marks. there should be 16.

[Crasher]

The change in pitch suggests a compression problem, you need to check your cam belt timing first.