Ignition problem - nooooo

[Dom]

After over a year of problem free driving, my car has started acting up again.
It starts pretty easily, but runs very lumpy, then pulls away and drives fine for 5 minutes before cutting out completely. The dash lights stay on, so the power is not lost completely, it just fails to spark. It then does not start for about an hour, just turns with the starter, but will not spark. After an hour, it starts again, but the same thing is repeated with the lumpy running and then the cutting out.

I have changed the spark plugs, plug leads, and I even tried swapping the coil, but the new one failed to work at all. 
The engine is fitted with a  Lumenition  electronic ignition module (so its not the points). Could the Lumenition module be playing up? The thing that baffles me the most is that it works for a short time and then cuts out - I can't work out what is triggering it. Any ideas?

What makes it worse is that there are so many modifications to the engine bay that the many of the usual culprits do not apply.

[chipuk]

Hi Dom.

You checked all the earths

[Dom]

I can never remember where they all are. The main grounding from crankcase to chassis is good.

Just completely throws me as to why it works (all be it a little rough) for a while, before completely cutting out and then starts again after an hours interval.

[chipuk]

Has the lumenition got an earth.

[bis13]

it sounds like something is getting too hot and then cutting out .

[Dom]

That's what i thought Mick, but it cuts out pretty quickly, before the engine bay is really that hot. That also doesn't explain the rough running. When it stops raining i will try and put the points back in and see if it solves it.



I think the Lumenition has an earth, but it would've been wired up with it originally and it has always worked. The only thing I have changed is the fan cover casing, to the silly Abarth type pictured below (not my engine of course).





This is currently not bolted on through all screws, so and is not connected to the head yet as i need to modify the rest of the cowling for this. Could this be affecting it in some way? It probably runs hotter because it is not connected properly as a lot of cool air escapes.

[bis13]

nah it sounds like an electrical unit is overheating and cutting out , go back to basics if you have the time to see what happens .

[Dom]

After stripping down the whole ignition circuit (apart form the ignition switch), replacing some of the wires and cleaning all earth's, the problem seemed to be solved and I had been driving my car for 2 weeks and about 75miles without any problems at all. However on Sunday I was driving along at a steady 45mph and it just cut out, as it had done previously and refused to start. It was turning over, but there was no spark at the plugs.

I tried to mend it at the roadside for an hour or so, changing spark plugs, ignition leads, ballast resistor etc to no avail. I had to call the RAC, yet again! After waiting close to 2 hours the guy turned up, had a little look and decided there was nothing he could do, so I'd have to be towed home, again. However the car was too narrow to fit on the dolly he had, so he kindly went back to his house (40min round trip) to pick up the adapter to enable towing using the leaf spring.

Anyway, after getting the car back to the 'rents place, i tried to start it, and guess what? it worked straight away, though it did cut out after about 2 minutes and would not start again. I am still none the wiser as to what it could possibly be. Something on the (electronic) ignition circuit is just not working as it should. There is the correct power to and from the coil and the lumenition module. What is timing out and stopping the spark?

[bis13]

replace the coil and see what happens.

[Dom]

Right now I am suspecting it is something to do with the Optronic switch connected to the distributor. There is 11.8V at the coil, so the ignition switch must be ok.

I think this also means the the module/amplifier is functioning, but I'm not 100% sure. I will try and run another couple of tests. What baffles me is that it runs fine for a bit (allowing the odd misfire), but then cuts out and fails to spark completely. None of the ignition components feel hot to touch as they are only on for around 4 mins before it cuts out.

I will try again with another coil, I did try this before and the 'new' coil failed to work at all, even when the old one was working.

 

[cos124]

did you get to the bottom of the problem?

[baron_matt]

I had a very similar issue on a 1992 Mexican made VW Aircooled Beetle. It would randomly cut out, turn over but not spark.

It was suspected to be the modern electronic ignition so I converted it back to original set up, changed back to a normal distributor, new coil, leads, cap the lot and do you know what....it still did it. Looking back  through the history paper work and I found references to starting issues probably the reason why it was sold.

Much head scratching was had by myself and the local VW specialist, until we had a eureka moment and found an additional lead on the coil terminal. This lead wasn't on any circuit diagram and then we found that it connected to a factory fit immobilizer which was faulty and was randomly earthing out the coil.

The immobilizer was disconnected and tossed merrily into the nearest dustbin and the car worked fine )

So check first, do you have anything connected to the coil that shouldn't be there?

Is the optronic sensor OK or is it covered in oil that could affect its operation?

Is the coil correct for use with the Ballast resistor?

If there is nothing obviously amiss with connections etc, then the only way to troubleshoot is to eliminate components in turn.

Is everything else OK with the Engine? Have you done a compression test etc.