RodSTI

I have a 2000 reg STI that has a lumpy tick over. I have replaced the plugs with 7s instead of 6s and set the gaps at 0.7mm. Now it is worse.

Ive checked the resistnce of the leads and they read about 7.5K ohms on the short side and 11.5K ohms on the long. This stays constant if i move them about so no breaks. I have fitted a strobe light in each lead and I am misfiring in 2 cylinders, one on each side. Is there any way I can test the HT module thing. Any Ideas why it should get worse with new plugs and less gap?

ALi-B

iTrader: (1)

Because you have double ended ignition coils (one drives 2 cylinders, one fires the front-most cylinders, the other the rear-most), a short or duff/lead/plug can show a missfire on the other paired cylinder making it look like a duff coil pack (i.e been there, seen it. done that ).

This also applies to a duff fuel injector, where a fuel related missfire "can" show up an ignition fault on two cylinders paired to the same coil (also been there, done that )

Also bear in mind a resistance test on leads does not mean they are ok as they could still break down under HT voltage and loose a spark to earth. I think there should be enough length to swap the leads for the front of the engine with the ones for the rear. If the missfire moves to the other pair of cylinders - you've found the problem - the leads.

If not, rule out a duff spark plug by swapping the fron most plugs with the rear most (yes, you can get duff plugs ). Again seeing if the missfire moves to different cylinders.

Failing that it's probably the coil pack is knackered. And that's where the bets lay (after doing the above tests),

There is a remote chance of the signal driving the coilpack is dodgy pointing to ignitor module or ECU(doubtful), or a fuel injector problem (again very doubtful).