Subaru Legacy TT misfire

foto-gifts, Oct 6, 8:38pm
94 BG twin turbo with 155Kms has an Intermittent misfire at warm idle. At a stop light it will have a wee cough and I can hear a click from the engine bay. Idle the car in park and neutral its fine but will cough badly if I turn the AC on.

Tracked the click sound to the drivers side (it sounds more like a snap really) and I'm certain its coming from the front spark plug area. Could it be coil pack, injector or spark plug! I can't see any cracks or signs of arcing from the HT leads.

Your thoughts would be appreciated

franc123, Oct 6, 8:47pm
The insulation tube on one of the HT leads has packed it in probably, and is arcing to the head. You may be able to see this by pulling the lead out until it hits the chassis rail, starting the engine and looking down the hole using a small telescopic mirror for any sparking. It would also be wise to remove the plugs and look for any tracking down the porcelain insulators.

intrade, Oct 6, 9:03pm
when has it last had a service like new plugs! you should also change leads from time to time so it wont fry up other things.

bmc460, Oct 6, 9:20pm
Start it up at night then ya can see if the leads are arcing.Had a holden ute do that untill we started it up in a dark shed then could see all the sparks.

hijacka, Oct 7, 1:13am
Twin turbo legacys never came out with ht lead they all have coil on plug but same sort of concept is applied.
They do change through the years but the early bg5/bd5 models pre 96 have coil pack that is surround with abs plastic and this plastic cracks due to heat so once the car is warm the crack opens more and thus arks out on the head more coursing it to misfire. They come out easy 1x 12mm and 10mm spanner is all thats needed. once out you can inspect them for cracking, let me know if you need any good replacements i have plenty of good single bolt coil packs around.

foto-gifts, Oct 7, 6:56am
Thanks hijacka will keep your offer in mind, and you maybe right as the problem appears really only after a spirited run and the car is hot; it's really bad if I turn on the AC. Cold and at warm up the car seems fine.

The car is 2 months old (to me) so a good tune up is on the cards