LPG Safety Switch

My GU TB45e Dual Fuel Patrol has a Peel CP30 safety Switch. The "Neg Coil" terminal has always had a wire which had a few turns wrapped around the number 6 plug lead and I always presumed that this was supposed to be that way. The car developed a peculiar misfire on both petrol and LPG, so after new plug leads, plugs, oxygen sensor, distributor cap, rotor and setting the tappets without a result, I weakened and took it to a mechanic in Adelaide who came recommended by another 4x4 driver. It cost me $210 to tell me I had not missed anything and that they thought it had either a broken valve spring of a bent pushrod but couldn'ty tell me more without removing the rocker cover.
I took the rocker cover off and did the tappets again (thanks to Patch697 for how to do it) and could see nothing wrong with either though I am not an expert. I have been musing over this for a few days and tonight I went out and took the wire from around the plug wire. Presto, the miss is now gone. Now I am worried that it might stop suddenly if this device decides to turn the gas off. Does anyone with the knowledge now why this thing could cause the miss and is it essential to the running? If so, where does this "Neg Coil" wire go on a GU Patrol with electronic ignition?

find the coil wires and tap iit in to the neg - by putting it round the spark lead it is taking the spark away from the plug so no fire in the cylinder hence missing

That device is your tachyometric safety switch. It's used to isolate the LPG if the engine stops. They work by sensing the ignition spark pulses so if the engine stops turning the LPG stops burning.:tongue:

Depending on the LPG system set-up your engine should either stop or switch to Petrol if that sense wire is disconnected from the spark source as you described.

Something odd there if it is staying on LPG and continuing to run... altho that Unit is much more sensitive than a mechanical Tachyometric Relay so meah... can't tell without seeing the vehicle

Whoever wrapped the sense wire around the plug lead is a bit of a knob really. Yes, it will sense pulses by inductions but if it is just "hanging out there" that is just asking for weirdrrse misses etc. if there aren't enough coils (or too many) or whatever causing LPG flow issues and other weird effects if it is disturbed.

A specialist LPG mechanic should have picked it. Not knocking the dude you took it too if he is not an LPG wizz.

I would be tempted to call into an LPG specialist (or get another opinion) for a chat and maybe even ask them to have a quick look.

Maybe there are other dody things in your LPG setup as well.

Thanks guys for the input which confirmed what I had been able to read on the web. The unit is shorted inside and does actually ground the spark pulses enough to cause the miss. The problem was compounded by a worn key in teh timing chain drive sprocket due to a loose harmonic balancer. All fixed now and new switch is on the way. Runs like a swiss watch now.