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My 1995 (3 doors) (6N1) 55 1.3 liters Polo dies suddenly while driving, the rpm-meter bounces also randomly. After the motor has stopped completely the rpm meter still moves randomly, and I can hear some relays going on and off very randomly. If you try to restart, the car will not start.

After about an hour the car will start again normally, and you can drive around 1 km before the car will die again.
The car will start immidiatelly after dying, if you spray "starter spray" to the carburator, but still the rpm meter goes just grazy, and the motor dies after about an 20 seconds.


Some background:
-Igniotion coil changed 1 year ago.
-Motor temperature sensor 6 months ago
-Gives no fault godes
-Motor grounding is ok
-battery charging is ok
-The problem is very random, drove just 2 months without any issues, and the it hit again.

Any ideas what could be wrong?

ALSO, while driving I hear a buzzing noise. The noise comes somewhere near the ecu. A strong hit to the top of the glove box has allways sent the noise away.Could the ecu really have gone bad?

Sounds like you have an earthing issue for sure

How are your sparks and spark leads?

If its a 95, it could well be an SPI rather than an MPI model which is a carry over from the mk3 platform.

Where are the earthings that should I check? Should the Ecus body be grounded? Atleast the ecu to body connetions looked a bit corroted.

If it is an earthing problem, how would it explain that the problem occures only after a while of drive?

Spark leads are ok. Spark plugs have been changed 50 000 km ago. Would it be a good idea to give them a change?
Yeah I guess it is a SPI actually.

I cleaned temperature sensor contact and hall sensor contact. Also changed ignition coil grounding cable, and sprayed electronic spray to distributor cap. No help, still the same problem...
ANY IDEAS?

I bought a new ECU, and I am waiting on it to arrive. Should the ECU body be connected to ground?

EDIT:
I checked the fuse box grounding, it is okay. Removed radio to find out where the buzzing noise was comming. Turned out that it is probably the heater relay under the passenger seat. I will try to check that next, but my theory is that the ECU is bad or badly grounded and therefore it makes the relays go on and off very randomly..

Yes ECU should be grounded to negative

Sparks are probably ready to be replaced

Redid the ecu grounding. The spark plugs seemed okay.
Any more ideas?

Changed ecu. Still not working. I am getting desperate... Ideas?

Changed the spark plugs and fuel pump relay.
After the engine was warm while I was driving on 3 gear, engaged clutch: same problem, revs jumping and the engine shuts down.

What should I try next? Fuel filter, ignition coil (and control unit for it, hall sensor?

Im not sure its the fuel filter, but give it a go.

Could be a faulty hall sender

Changed ignition coil, still the same problem, arrrgh..

The hall sensor wires get only about 11,4 volts. Could this be it? The ground wire is solid, but the + wire gets only 11,4 volts.

For anyone having the same problem: It was probably the hall sensor.

Dunno if this is of any use to you, mine did something like yours a yr or so ago, after MUCH hunting, the mechanic finally discovered it was the coil pack, it was faulty, didnt think it could be that as it had only been changed about 3 months prior. the little metal & black square jobby on the engine bay wall, under windscreen, near the engine cooler tank.

It was the Hall sensor, as I said earlier.
Anyone having same kinds of problems: Ignition coil or Hall sensor. I wasted wayyy too mutch time hoping it was just a relay etc..