LPG and Wasted Spark

[McRover75]

I have the old dodgy distributor woes and rather than spending my money on fixing it I am considering going the MegaJolt route.

However I have heard that wasted spark can cause ignition in the inlet manifold on the exhaust stroke. I could perhaps understand if the timing was way out (ATDC) that the exhaust/inlet valve overlap may allow some mixture to enter the manifold which could potentially get ignited. But other than that to me it seems like a load of bollocks for a rover motor. Further to that the later disco's and P38 run wasted spark anyway, so does this "problem" exist?

Can anyone potentially shed some light on the matter?

[bee utey]

"Waste spark" engines are more prone to LPG backfiring, however surprisingly so do individual-coil-per-cylinder engines. I doubt if it has a lot to do with igniting residual fuel, as there is plenty of exhaust gas being expelled during the waste spark moment. I suspect it's more likely to be electrical interference generated by the bundled primary wiring. High tension leads can be separated to good effect, low tension ones generally can't.

Tens of thousands of VN-VY Commodores, EF and AU Falcons manage on waste spark systems without too much of a problem. The plug gap should always be kept to around 0.6-0.7mm for LR V8's with coil packs on LPG.

BTW you will save huge amounts of money if you track down a good second hand dissy and fit a Bosch BIM024 ignition module and a matching coil. I do tons of these conversions, they give very little trouble. Thread here:

http://www.aulro.com/afvb/technical-chatter/96950-lucas-ignition-amplifier-replacement-bosch-024-a.html

[McRover75]

Cheers bee utey,

I had the same thoughts on the exhaust stroke but never thought of the potential chance of crossfiring between coil packs.

Megajolt does give a best of both worlds but I barely run on petrol anyway so it really is not a huge deal.