problems with 3 pin coil packs

[andrew_wilks]

Hi I have a 96 subaru legacy RS with a 98 engine that runs 3 pin coil packs on the individual spark plugs. as of last week the #4 cylinder coil broke (got hot and burst)
I got a new coil and replaced the old broken one and the back swelled up like it was going to burst. so I swapped the spark plugs and coil packs round. But I still have the same problem with #4 overcharging, I've gone through 3 coil packs now. is this a control short or ecu failure? the car runs fine (doesn't miss) when a new coil is introduced, but coil will fail after aprox 45 seconds of running. Even when the ignition is on but the engine is not running the coil swells up and gets hot (ready to blow). Any help or info would be greatly appreciated thanks.

[ouch1011]

Without seeing a wiring diagram for that specific model (which I don't have) I can't answer for sure, but the 3 wires should be B+ (power), ground, and then a control signal from the PCM. Most 3 wire coil-on-plug systems have a transistor mounted on the coil that receives a signal from the PCM to switch the current to the coil on/off. For coils to be repeatedly melting down in such short order, I'd say the coil is being constantly switched on. Ignition coils actually draw quite a bit of current but they typically only do it for a very short period so they don't build up much heat. If it is on constantly, it will melt down quickly.

[andrew_wilks]

cheers, I think its an earth problem. I had a couple guys do the auto to manual transmission conversion last week and after putting everything back together the top earth that goes to the intercooler bracket was left off. I think that may have short circuited the wiring or ecu due to the computer trying to compensate for lack of earth or something. now I just have to find out which one it is. so could be a case of new loom and/or ecu...... or neither.