Icey weather - intermitent fault

[philKS2]

Gawd... what's going on?

Three weeks ago the car (S2 ABY) wouldn't start on a frosty morning.. AA came out, could not get it going, and said it was probably crank position sensor (or somesuch)

They towed me into garage... BUT by the time the garage took a peek a day later, the car started first time and seemed ok.

She's been running fine since... and then today.... ice on the windscreen, and she won't start again. Lots of go in the battery, but no sign of firing up.

Thinking of breakig out the hair drier to warm her through.

Any ideas?

P

[S2central.net]

I'll wager its CAMSHAFT position sensor - the infamous hall effect doobry (G40) - you could try a hairdryer on it or some gentle percussive therapy...

The ECU needs this signal to start the engine. Lots of info on it here - do a quick search if you like.

You normally hear of them playing up at high temperature - when a trickle of Evian over it usually does the trick.

[Jas11n]

Any ideas?

P

Checked for any fault codes?

[Fat Audi 80]

I agree with Paul, money says its the cam position sensor, water did the trick for me and it never came back again..

Good luck.

Cheers,

Steve

[S2central.net]

Another thing to check is that the fuel pump is activating when you crank the key... The relay *might* be sticky with the cold weather - try some gentle heat in the fusebox area - Relay 3 from memory but its on the label. You do hear about the odd one of these relays just dying - I always mean to carry a spare one just in case but not got one yet.

[Crawford_S2]

Long shot but along the lines of what paul was saying about relays. I had a prob where my fuse box cover was not on properly and got all dmp in there. Worth a ook too.

[philKS2]

Thanks... and esp for those of you that offered advice when this first happened to me.

Please bear with me as I'm not up to the technical standards of so many on here...

1- Jase mentions fault codes... do I need to plug in something clever to reach them... I don't know!!!

2- The AA guy who came out literally spent 15 secs fiddling with the electrical connector right on the front of the engine, which he redckons is a connector to the infamous Hall thingy Camshaft Position Sensor ... The spring clip was missing and he reckons the connector had just worked loose... I hope I've atatched a pic (used a random engine pay photo, not my car!) to show the clip I mean.

Is this something to do with the Hall Thingy??

Anyway once the AA man touched it (with his divine magic hand) - he turned the key and the cra roared into life... been ok since, and now has a plastic tie holding the clip in place

Lesson (assuming the fault IS cured and doesn't come back tomorrow) LOOK FOR THE SIMPLE THINGS FIRST!!!

[S2central.net]

YES - thats the chap...

That connector is for your camshaft position sensor. 10/10 to the AA man for spotting that.

When you get some time, surf over to S2central.net and look thru the technical pages on how to get fault codes from the engine - either with a test lamp or VAGCOM software.

Paul

[Fat Audi 80]

you could see if Waad is still doing these: http://www.s2forum.com/forum/showthread.php?t=24390

They are great for the occassional fault finding session!

(You will still need Paul's Fault codes from s2_central)...

Cheers,

Steve.

[philKS2]

(Thanks Steve and Paul for help.. am chasing a blink code box, or will make one myself...)

UPDATE.... weds... OK so can anyone please exklain or help... Two more icey mornings, and each time fiddling with the possibly loose camshaft position sensor connector seemed to do no good... so in desperation and disbelief I got a small bottle of water and poured it down the back of the cam belt... and BRRRRMMM BRRRMM the car started straight away. I apologise for thinking this sounded like a dotty solution. It works. I'm also revising my position on Tooth Fairies and Father Christmas.

SO... questions questions.... given that i don't want to have a bottle of water as part of my engine starting routine every day...

1- what's actually happening.. presumably the cold is causing the sensor to stick?? How is the water helping??? Is it just shorting the thing out?

2- How tro cure long term - a new sensor?? It looks like a tricky position..so could I get udner the car and remove/clean it out?

P

[ericd]

from memory its a vane effect hallsender , they're ain't really anything to "stick", I've never really understood the root cause failure of the sender itself, might open my own old one and have a look, any electrical circuit/component is influenced by temp, hot or cold, they're failure mode differs, cpus don't like heat and cache don't like it cold, similarily 12-15 year old wiring and connectors tend to fail .

you're just seeing the death throes of your sender, only interesting thing you mention is that the retaining/securing clip is missiing, peel back the rubber boot of the connector and check the condition/security of the 3 wires in there, also give the connector a quick blast with some electrical contact cleaner (de-icer would do), also try taping the connector together and see how it goes

[philKS2]

UPDATE Sunday 7th Dec 2008
I'm documenting this to help people in the future with similar probs involving non-starting and the Camshaft Position Sensor

ONE - BLINK CODES : Paul Nugent's www.s2central.net instructions on how to get diagnostic "blink codes" ... Thanks Paul I bought my 39p Maplin LED bulb and followed the instructions on your website. The blink code system is indeed simple to understand, and works well.. it comfirmed a fault with my Camshaft position sensor, the dreaded Hall Effect sensor.

TWO - CONNECTOR : I did also unplug the connector for that sensor, which is on the fornt of the engine - see previous photo, and cleaned out, checked the wiring connections and used spray on electrical connection cleaner.. this did NOT clear the fault. I need a new spring clip for this, and have used a plastuic tie to hold it firmly in place for now.


THREE - WATER : I have found that (following advice from others above) pulling back the plastic cambelt cover a little and pouring a cupful of water down the back of the cambelt DOES indeed temporarily cure the problem...and the car will start straight away most times after this is done!! However as my start-up problem happens in the cold (no prob on warmer days last week) I found that using HOT water works on cold days, when cold water does not !


I'm now booking the car into my friendly garage (Brooklands in Bristol) to get the Camshaft Position Sensor replaced, at it looks too tricky for a mere amatuer like myself.



PhilK

[quattrodude]

Did you do the test with the engine running as i do know with the VAG systems it will show crank positon senser and maybe hall sender when not running, as there is no signal to be read because the engine is not spinning.

I only no this because it boggled me for a while trying to work out how it would fire if the two most important engine senders were not working

Yes I no im stupid ha ha

[S2central.net]

The only fault code when not running is for G28 - the RPM sensor...

I'd love to know the science behind why the water trick works (err sometimes anyway).

As to changing the sensor - its not too bad a job but there is one particular area where the garage MUST be careful. Highlighted below in this rough sequence...

1. Front bumper off

2. Intercooler and x-member off (maybe aux rad too if it doesn't co-operate)

3. Timing belt cover off

4. Confirm engine timing with camshaft and crankshaft pulley marks at #1 TDC

5. Reduce tension on timing belt. IMPORTANT - no need to touch any crank pulley bolts unless the timing belt needs to be renewed.

6. Tease the timing belt off the camshaft pulley.

7. Loosen the camshaft pulley bolt that secures it to a camshaft. VERY IMPORTANT - A suitable 'counterhold' tool MUST be used to secure the camshaft pulley during this operation to prevent stresses on the keyed tab on the pulley.

8. A couple of bolts secures the offending sensor to the front of the head and its job done.

9. Refitting in reverse with same note on use of counterhold on the camshaft pulley when being refitted. I can't remember torque on that bolt but can look it up if necessary.


Cheers,

Paul

[Nuvo]

I'd love to know the science behind why the water trick works (err sometimes anyway).

I would think its down to the hall effect ICs open collector NPN output transistor overheating. I'm sure if you cooled the device with freezer spray you would see it start to work again too.