I had the Head gasket of my 1995 subaru imp wrx recently replaced. Since then on full boost the engine would misfire. Replaced the spark plugs still the problem persisted. Since yesterday the engine is only firing on 3 cylinders Very disappointed . Could anybody advice
Best Regards
RTGP

 

It could be ht lead, Start it up and pull off each ht lead one at a time to find out which cylinder is not firing might be a case of new ht leads

 

as its a 1995 its on coil packs, they are very common to crack and cause the issue your having.
hth

 

Thanks for your replies. Shall investigate that way and keep you posted
THX KENT SCOOBY & JDM STIG

 

Had missfire on start up. Turned out to be damaged coil pack - X reg classic. New coil pack + leads + plugs, fixed it and made it louder lol.