Audi 80 stopped! - El Dingo (Martin)
There I was, after a long hard week (Wednesday in Birmingham, Thursday in Bradford, Friday in Watford), cooking up a 'Kofta Bhuna', when the wife (some call them SWMBO, but I don't know what this means - is it Short Wife Might Bale Out? *having an amphibious car?*) called up to say that the car had broken down.

Well, I put the cat out, put the lid on the cooking and went to investigate. A quick check with a key stuffed up a plug lead showed no spark. The engine turns over beautifully and (paranoia in charge) I even prised over the cam belt cover and *yes!* it's still there! Fuel seems to be there (singed hair).

This car has a distributor on cam 1 and a rotor arm, from a mini coil (I've never seen one so small - perhaps they should contact family planning).

I'll have to go out in the morning and fix it roadsides....

Martin.
Re: Audi 80 stopped! - El Dingo (Martin)
...any good ideas backroomers?...
Re: Audi 80 stopped! - David Davies
Common problem is failure of the coil/amplifier unit-it looks like a small ignition coil but in fact contains the ignition amplifier as well. Advise only use OE updated part. Strong possibility that this is the fault area.
Re: Audi 80 stopped! - El Dingo (Martin)
David,

Thanks, I'll check this out... I'm going out to the car this morning.

Martin.
Re: Audi 80 stopped! - Alwyn
Martin.

I owned an Audi 200 turbo some time ago. That would stop from time to time and it turned out to be the "Hall effect" sender on the distributor.

Got one on yours?
SWMBO - PDP
(She who must be obeyed)
Re: Audi 80 stopped! - El Dingo (Martin)
Firstly, thanks PDP for clarifying SWMBO, but I think my version is more fun!

I discovered that the system is Bosch Motronic with base unit (behind the glove box), knock sensor, Hall sensor (on the distributor), power module, coil and distributor...

A few hours of fault finding and two calls to my local Audi dealer and I think that I have located the fault - in the Hall sensor (Alwyn - you were right! BTW Did you like the 200 turbo?). As I can't get any parts now before Monday, I'm going to have a 'fiddle' with it tomorrow.

Martin.
Re: Audi 80 stopped! - phil ireland
Alwyn

Enlightenment please - whats 'hall effect' when its doing whatever it is its supposed to do/or not do as case may be?
Re: Audi 80 stopped! - Robert
The Hall effect is a physical effect:

www.warwick.ac.uk/~phsbm/qhe.htm

It combines electricity & magnetism and basically says that the resittance of a material (semiconductor) is changed according to the magnetic field applied to it.

In the context of a car, it is used in ignition systems and ABS sensors to good effect. The sensor is placed very close to a rotating part which has a single (in the case of of ignition) or multiple raised, or lowered, areas. When these pass by to (very close) the sensor the sensor output then changes as the shaft/etc. rotates.

With ABS this produces a stream of pulses per wheel that allow the ABS control unit to know when the wheel has stopped/stopping. Many pulses per rotation, maybe 50 or so.

With ignition, the single pulse is once per revolution and may indicate TDC by suitable placement of the sensor or delay in the electronics.

I hope this helps.

Regards ............ Robert
Re: Audi 80 stopped! - Mike Harvey
Good site from Warwick which I've bookmarked. I think you may have got hall effect and inductive pulse mixed up on the 'visual' though. Hall effect has a vane or similar which blocks the magnetic field, the inductive pulse type has the 'raised and lowered' parts as you describe, or holes or teeth. They are not used very often with ABS. 3 wires from a hall effect, 2 from inductive pulse is the quick way to see which you have. The beauty of hall effect is that it is a switch, so you get full voltage every time. The inductive pulse output is speed sensitive, ie slow' low voltage, fast, higher.
Regards
Mike
Re: Audi 80 stopped! - El Dingo (Martin)
Hooray!

Car is fixed, thanks to the helpful scrappy at High Heavens (near High Wycombe).

The Hall sensor was to blame, and I got a similar one out of another VAG distributor (the guy searched through the pile of distributors until he found a similar looking sensor).

Interesting to see the discussion about 'Hall Effect'. The unit in my distributor has three wires, +, - and signal. The 'encoder' is basically four cut-outs in the 'cap' under the rotor arm (leaving four square teeth).

I discovered that the quick way to test the unit in the car is to use a diode tester (or digital multi-meter with that function) across + and signal wires with the power stage socket removed - then spin the engine on the starter.

Thanks for the help and input!

Martin.
 

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