Very Strange Ignition Problem with LEBURG system

Barber · Post by **Barber** » Sat Oct 18, 2008 7:00 pm

Hi Folks

I'm banging my head against a brick wall with a strange VW ignition problem. The engine is a VW1834 with Leburg ignition. Having just changed to the HT leads in an attempt to try and eradicate some Radio problems I have found a problem which may have been there for some time. Using a simple inductance tachometer on the HT leads to verify a good connection I have found that only 4 of my 8 plugs are firing. Indeed I may have been flying like this for several hours! However, there is a strange symmetry in the problem which I can't get my head around.

The system has two ignition controllers and each one feeds two coils (4 coil packs in total with two leads from each). Basically each coil pack only has one working plug. From this I can deduce that neither of the ignition controllers are (completely) faulty. It also seems too coincidental that each of the 4 coils has a faulty outlet on it.

I'm at a bit of a loss on this one and don't want to bug Dave (Mickleburgh) about it. Any ideas would be welcome.

Thanks
Tony[/img]

Steve Brown · Post by **Steve Brown** » Sat Oct 18, 2008 8:38 pm

I think this system operates under the 'wasted spark' principle so whenever a cylinder fires 'for real' at the top of the compression stroke, a corresponding 'wasted - does nothing' spark is fired at the top of the 'paired' cylinder at the top of its exhaust stroke.

Without knowing your inductive tacho I suspect there may not be a problem - it just may be that the tacho isnt picking up the 'negative' spark. The sparks of each paired plugs doesnt actually spark to earth - rather they spark completing a high tension circuit (of which the coil and engine mass and 2 plugs are part) between themselves

I think your best bet is to mark everything up ie left ignition no 1 cyl , right ignition no 1 cyl etc (so you know what you are starting from!) remove all the plugs from each cylinder to prevent any risk of firing then reconnecting up the plugs to their respective leads, and crucially to prevent ignition damage - ensuring the plugs are connected/touching against the engine to complete the sparking circuit.

Then 'kill one ignition 'side' as if you are doing a mag check. Then turn the prop briskly enough to get each plug of the live ign side to fire in turn. You should soon see which two plugs are firing paired together - and indeed whether they are firing at all. There should be a spark for each cylinder for 2 full rotations of the engines ie 4 sparks at each spark 2 plugs will show a spark .If not your spark plug leads are wrongly connected perhaps when you changed the leads?

.

Then repeat for the other side.

I believe the order of firing is 1432 in which case I would expect cyl 1 and cyl 3 to be paired 'spark together and cyl 4 paired /spark with cyl 2

Report back & let me know how you get on.

Regards
Steve

PB · Post by PB » Sat Oct 18, 2008 9:36 pm

Steve is correct.

The system uses a 'wasted spark'. In simple terms (if the thing is running correctly) all four plugs in the front two cylinders spark when they are appropriately near TDC followed by all four plugs in the rear cylinders 180 degrees later.

I think you will find that if you take the plugs out and rest them on the engine you will find you are getting a good spark on all plugs as required. If not, it should show with a RPM drop (or engine stop) at a simple right-left check.

If you are used to magnetos, it's uncanny to see a whacking great big spark as you gently push the prop (backwards or forwards) past 6 degrees after TDC with just your fingertip. You can see why the engine starts so easily with this system!

Barber · Post by **Barber** » Sat Oct 18, 2008 10:51 pm

Well that makes perfect sense now. Thank you Steve, Dave, PB. I did think it was odd and the engine didn't appear to be misfiring or running on two cylinders on the IGN check. I know this was one of the early systems but it had been unused for several years.

As an aside, the antenna has been changed and I have got a LDO regulator (just have not yet fitted it yet as I'm not sure on how the wiring goes yet - need to do some more cable tracing!). The old HT leads were very low quality unsuppressed. Just have not had a chance to fly it yet to see if this has made any difference.

I suppose I could have used the inline testers that you can buy for a couple of quid and this would prove conclusively also.

Your thoughts much appreciated Gents.

Tony

PB · Post by PB » Tue Oct 21, 2008 8:39 pm

On my Nipper with Leeburg ignition I use high quality KV85 ignition leads from Magnecor http://www.magnecor.co.uk/productinformation.htm
with standard (no resistor) spark plugs.

I have a Filser TRT600 radio. There is absolutely no ignition noise whatsoever. I do have a very low level of alternator noise (hum) which is current related. If I leave the master switch on by mistake and the voltage is a bit low, the noise increases for an hour or so until the battery is fully charged again (but please don't try and fly with a significantly low battery).

I guess the radio noise could be alleviated with a ferrite in the feed close to the radio and possibly a capacitor across the input. To be honest, the noise is so low I have not bothered.

Barber · Post by **Barber** » Tue Oct 21, 2008 9:29 pm

Having started this thread off in search of an ignition answer (which I have) it sort of leads onto another issue. More research (The net is a wonderful thing) would suggest that others have had problems with the ICOM A6 radio unit also so I'm going to try and find someone with an earlier model to try - trouble is you can't get hold of them any more, probably for that very reason. Anyone else who has had problems with A6 radios, I'd be interested in hearing your experiences.

I do have a noise filter on the services supply and am going to fit a LDV regulator as suggested.

Regards

Tony