First, the Groupner system modified the XPS system and had problems. If you get the genuine XPS system you will have no problems.
2.4 is very resistant to interference. It employs spread spectrum that was developed for that purpose. However if you wipe out the entire band it will be interfered with.
The gas ignition system in use depends on ground connection thru the shield. If you have an intermittent connection in the shield you will get a spark there that will wipe out the band and kill your system.Mag systems were grounded internally and the spark plug wire required no shield as long as you used a resistor plug.
To guard against any interference, wrap a bare wire around the plug cap and ground it to the engine.