Mk1 switching off randomly

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JunaVivo
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Mk1 switching off randomly

Post by JunaVivo »

Hi gents - I really some help on this issue as I am losing my mind here.
Mk1 1500 carb, with electronic distribution (previous owner did the conversion).

So the issue is, the car drives perfectly fine but randomly switches off whilst driving and does it almost instantly. The issue is mainly present when its warm/hot/standing in traffic however its happened while the engine was cold as well. Some times it would immediately start up after switching off, other times I have to wait about 15 minutes before she eventually starts up and I would be on my way again like nothing happened. But its happened at the worst of times - peak hour traffic and has now become a daily occurrence.

Basic trouble shooting:
1. Checked for spark by unplugging the coil lead from the distributor and it would spark while swinging the motor. The led me to believe it was fuel related.
2. Checked for fuel and fuel was present at the filter, but just for good measure I replaced the fuel pump, fuel reservoir and eventually the carb with GW a replacement.This improved the performance/economy but the issue still persisted.

3. When it switched off again, I checked the carb, pumped the accelerator and I could see fuel spraying in. After doing some more research, the symptons now appeared to be an electrical/spark issue due to immediate switching off. I unplugged the coil lead and tried to start and spark was present but it just wouldnt take, or would take & die almost instantly.

4.Changed the TP100 module and bought a new wiring harness and rotor from GW. Wired it correctly and she starts on the turn. Unfortunately the issue didnt go away. Drives perfect for a day or two & randomly switches off.

5. Next up, changed the coil and coil lead as the one in the car looked old.(Out of desperation bought one from midas as they were the only shop open till 6pm), but the car still switched off the next day. What I did noticed is that the coil was very hot (unable to hold for too long) at the point when the car switched off, and after it cooled down I could drive normal again. So apparently the midas coil (no name) is not the right one.

6. Bought a Huco (red) coil, as apparently this is the right one. Connected and it started up on the turn, but I havent driven the car to work today.

7. I checked the wiring and 100% certain the the TP 100 module and the coil is wired as per the diagrams on the forum. An indication of this is that she starts on the turn and drives normal when she is behaving.


So my questions to try and norrow down the fault:

a.) Im convinced that the issue is spark related, but would really appreciate your thoughts / advise ?
b.) Even though spark is present, is there something as a "weak" spark that would not be enough to start the car/cause it to switch off? What would cause this "weak" spark?
c.) What would cause the coil to get hot to the point where it stops working/ gives out a weak spark and has to cool down before working again?
d.) Is the Huco coil the right coil for this vehicle - or should I look at a different brand?
e.) Could the tp 100 be the culprit although its a new one?

What else should I be looking at?

Please guys, I am desperate for help. :cry:
79 MK1 GLS 1500 - Stock Standard
Citi 2.0 - 8V Performance
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panic-mechanic
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Re: Mk1 switching off randomly

Post by panic-mechanic »

often the main ignition switch ie. The thing behind your key is the culprit for these problems.
Somot makes bad contact for a moment and kills everything.nthen when you cycle the ignition it makes contact again and the issue disappears.
Check this by temporarily wiring a voltmeter to the coil+ and watch what happens to that power when the car dies.
Stephan van Tonder - Jhb - Putfontein Benoni
'05 Audi A6 3.0L TDI Avant
'09 Touareg 3l TDI
'13 VW CC 2l tdi (repair project)
'05 Touareg v10

Perfect Power dealer. I do dyno tuning.
JunaVivo
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Re: Mk1 switching off randomly

Post by JunaVivo »

Thanks Panic. Will do the test and will feedback with results.
79 MK1 GLS 1500 - Stock Standard
Citi 2.0 - 8V Performance
JunaVivo
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Posts: 78
Registered for: 12 years 1 month
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Location: Roodepoort

Re: Mk1 switching off randomly

Post by JunaVivo »

Hi Panic

The issue is still persistent.

I checked the voltage to the coil + at the point of cut-off over the past few days and voltage is consistently between 11.8v -12.3v

Symptoms are same, will start normal after 10 mins or so and drive like normal, and suddenly it would cut-off. No spluttering, stalling etc.

Since then changed the plug leads, but no difference.

I've pretty much changed all the electronics except the distributor.
Can a faulty distributor display such symptons?

Your assistance is much appreciated.
79 MK1 GLS 1500 - Stock Standard
Citi 2.0 - 8V Performance
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panic-mechanic
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Re: Mk1 switching off randomly

Post by panic-mechanic »

Ok please describe your testing method at the point where it dies. Did you mount a voltmeter inside the car to see if there was a voltage cut - or at the point that it died got out - opened the bonnet and then measured 12v yet it would still not start.
At that point did you check if there is spark?. and that fuel is present at least in the filter.
The issue is that one of the items disappears and you have to figure out which.
So either there ain't spark or the carb has run dry.
Stephan van Tonder - Jhb - Putfontein Benoni
'05 Audi A6 3.0L TDI Avant
'09 Touareg 3l TDI
'13 VW CC 2l tdi (repair project)
'05 Touareg v10

Perfect Power dealer. I do dyno tuning.
JunaVivo
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Posts: 78
Registered for: 12 years 1 month
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Re: Mk1 switching off randomly

Post by JunaVivo »

Thanks Panic.

I opened the bonnet and measured the voltage after the vehicle cut out, and at that point it still would not start.

Fuel is present at the filter. Im also driving with out the air filter (for purposes of testing) so I can also confirm that fuel is present in the carb, and therefore inclined to believe its spark related.
79 MK1 GLS 1500 - Stock Standard
Citi 2.0 - 8V Performance
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Re: Mk1 switching off randomly

Post by panic-mechanic »

Ok so then if it has 12v and no spark you are left with the elements of the ignition system
So coil, coil amplifier and the hall generator.
Stephan van Tonder - Jhb - Putfontein Benoni
'05 Audi A6 3.0L TDI Avant
'09 Touareg 3l TDI
'13 VW CC 2l tdi (repair project)
'05 Touareg v10

Perfect Power dealer. I do dyno tuning.
JunaVivo
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Posts: 78
Registered for: 12 years 1 month
Car Make: Volkswagen
Car Model: VW
Membership No: missing
Location: Roodepoort

Re: Mk1 switching off randomly

Post by JunaVivo »

Thanks Panic. I changed the distributor over the weekend. Seems to be working fine now. Will monitor over the next few days and feedback.
79 MK1 GLS 1500 - Stock Standard
Citi 2.0 - 8V Performance
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