N reg 2.8 Quattro will not cold start

[megavolt]

The car normally starts and runs fine. During very cold weather, if I turn the engine over immediately when getting in, it will not fire, even with plenty of battery. It may then refuse to start for 30 mins or so.

If I wait a few secondswith ignition on, even from cold, it will fire up immediately.

Any assistance would be appreciated.

Kind regards,


Megavolt

[kenney]

Engine code????????

[megavolt]

Hi Kenny,

Engine Code is AAH. Full number is AAH251217

Thanks!

[kenney]

This has the symptoms of a faulty temperature sensor.Can you get a fault code read?

[megavolt]

Not today as it's stuck in the driveway and can't move it yet. A colleague of mine has also mentioned a temperature sensor, although I am not sure how many or where they are located.

Is there a common one which plays up or is that being a bit naive and hopeful?

[kenney]

There is only one,situated on the large coolant pipe at the rear of the engine,it's on right hand side

[megavolt]

Hi Kenny,

Located it (I think). The rubber cover has been disturbed so it may have had some attention at some time, although it's certainly not new.

Is it something I should short out, open circuit, or maybe just get a hairdryer and heat up a bit????

[kenney]

The only thing you can do,is measure the resistance,to see what information it is feeding to the ECU with 10 degrees should have 4k ohm and with 90 degrees abut 400 ohm.

[megavolt]

Now that I could do! Meter out, but difficult to get a reading. So I cobbled together 3 x 1.5k resistors and stuck it up the connector receptacles..

Fired up instantly! Kenny - many thanks! Don't know what I would have done without your help and knowledge - apart from maybe have to get a taxi to work tomorrow . . .

Kind regards

[megavolt]

;) As an update:

I was ok with this 'fix' of 4.5 k ohms but also ordered a new sensor. My local garage connected their computer and confirmed that there appeared to be a problem with the coolant sensor as well as a couple of sensors associated with the camshaft - to be investigated later.

The problem with this fix is that it also fed too much fuel into the system when the engine was warm, and tended to flood the engine. I did change to a 330 ohm resistor, once the engine was warm, and that proved most useful, as well as reducing fuel consumption!.

The worst time was on the Tuesday morning, when the 'fix' didn't operate at -2 deg C. Whilst Kenney was entirely accurate in his information, 4.k ohms at -2 deg C was not enough, and the car remained lifeless from 7.30 a.m. until 9.30 a.m. On further investigation, that value should have been about 6 k ohms+ for zero deg.

I fitted the new sensor last night. This morning, with -2 deg C, it fired up first time and has continued ok all day, so some hope that this was indeed the problem.

However, I checked out the old sensor, there was some moisture and general muck inside the contact area of the sensor. This would have provided electrical conductivity which may have made the actual resistance of the sensor appear lower than it was (i.e. the engine temperature appeared tobe higher than it was). This was a possible cause of the problem.

I recall that the rubber boot was not secure over the connections, so it is possible that moisture ingress could have passed through the top of the wiring connector into the area of the connection to the sensor. Whilst that has been rectified, I may still 'silicone' the entire connection to prevent future problems.

However, so far, so good! Problem fixed!!

Thanks once again to Kenney for his help in identifying the problem!

[kenney]

These sensors are very sensitive,and as often as not,it is the contacts that are at fault.The contacts on the connector should be replaced with gold plated contacts,this insures no further problems.

[megavolt]

Hi Kenney,

I would agree with your comment in general as it is accepted that gold has the best conductivity and resistance to corrosion of all materials.

Your comment would be supported by the fact that the computer error showed the sensor as being an intermittent fault.

Not sure if the new one has gold-plated contacts, but now it's working, and using the 'if it 'aint broke' epithet . . . guess I'll leave it awhile, knowing that a bit of wet and dry may cure the same problem in the future. . . .:beerchug: